Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing [1 ed.] 9781635507201, 9781635504682

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Authors Glen M. Tellis and M. Hunter Manasco use their experiences in the classroom to inform their approach to student learning. Each topic is concisely introduced in bullet-point form and then augmented with more detailed text, boxed content, illustrations, and tables. This is the only text with real cadaver images from Anatomage’s 3D dissection table allowing an unparalleled glimpse into the anatomical structures of the human body, featuring true-to-life colors with an impressive level of detail.

Key Features: • Unique bullet-point format to increase comprehension and retention • 340+ color figures boost student engagement and include both anatomical illustrations and real human cadaver images fromAnatomage’s 3D anatomy table • Chapter learning objectives to guide instruction • Boxed features with historical and cultural contexts • Bolded key terms and glossary

Glen M. Tellis, PhD, CCC-SLP, F-ASHA, a Board-Certified Fluency Specialist, is a professor and chair of the Speech-Language Pathology Department at Misericordia University in Dallas, Pennsylvania. He completed his doctorate at The Pennsylvania State University in 1999 and has over 24 years of experience, including teaching anatomy and physiology courses. His research interests encompass fluency disorders, dysphagia, multicultural issues, research designs, treatment efficacy research, advanced digital technology, and clinical outcomes. Dr. Tellis frequently presents nationally and internationally on near infrared spectroscopy and hemoglobin concentration in the brain. He has published extensively and is a best-selling author of numerous textbooks. Dr. Tellis has continuously received externally funded grants for his research. A few of his professional achievements include serving as the past president of the Pennsylvania Speech-Language-Hearing Association, chairing ASHA’s Academic Affairs Board, receiving the Honors of the Pennsylvania Speech-Language-Hearing Association, and becoming an ASHA Fellow. M. Hunter Manasco, PhD, CCC-SLP, is a professor in the Department of Speech-Language Pathology at Mississippi University for Women in Columbus, Mississippi. He completed his doctorate at the University of South Alabama in 2008. Dr. Manasco has worked as a speech-language pathologist in various professional clinical environments with a wide range of clinical populations from newborn to hospice care. He has over 15 years of experience teaching, including teaching anatomy and physiology courses. Dr. Manasco specializes in diagnosis and therapy for neurogenic communication and swallowing disorders. He has published and presented books and many papers within his areas of specialty.

www.pluralpublishing.com

FUNDAMENTALS of ANATOMY and PHYSIOLOGY of Speech, Language, and Hearing

Drs. Tellis and Manasco’s active learning approach will encourage and challenge students to think deeply and critically about the anatomy and physiology related to speech, language, and hearing. This immersive and technology-centered process is intended to increase student comprehension, retention, performance, and enjoyment of the material.

Tellis Manasco

Designed to meet the distinctive needs of today’s undergraduates in communication sciences and disorders, Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing provides an accessible and visually engaging comprehensive introduction to the structures and functions of respiration, phonation, voice, articulation, resonance, swallowing, hearing, balance, neuroanatomy, and neurophysiology.

FUNDAMENTALS of ANATOMY and PHYSIOLOGY of Speech, Language, and Hearing Glen M. Tellis | M. Hunter Manasco

FUNDAMENTALS of ANATOMY and PHYSIOLOGY of Speech, Language, and Hearing

FUNDAMENTALS of ANATOMY and PHYSIOLOGY of Speech, Language, and Hearing

Glen M. Tellis, PhD, CCC-SLP, F-ASHA M. Hunter Manasco, PhD, CCC-SLP

9177 Aero Drive, Suite B San Diego, CA 92123 email: [email protected] website: https://www.pluralpublishing.com Copyright © 2025 by Plural Publishing, Inc. Typeset in 11.5/14 Adobe Garamond by Flanagan’s Publishing Services, Inc. Printed in China by Regent Publishing Services Ltd. All rights, including that of translation, reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, recording, or otherwise, including photocopying, recording, taping, web distribution, or information storage and retrieval systems without the prior written consent of the publisher. For permission to use material from this text, contact us by Telephone: (866) 758-7251 Fax: (888) 758-7255 email: [email protected] Every attempt has been made to contact the copyright holders for material originally printed in another source. If any have been inadvertently overlooked, the publisher will gladly make the necessary arrangements at the first opportunity. Library of Congress Cataloging-in-Publication Data: Names: Tellis, Glen M., author. | Manasco, Hunter, author. Title: Fundamentals of anatomy and physiology of speech, language, and hearing / Glen M. Tellis, M. Hunter Manasco. Description: San Diego, CA : Plural Publishing, Inc., [2025] | Includes bibliographical references and index. Identifiers: LCCN 2023022249 (print) | LCCN 2023022250 (ebook) | ISBN 9781635507201 (hardcover) | ISBN 9781635504682 (ebook) Subjects: MESH: Speech--physiology | Language | Hearing--physiology | Nervous System--anatomy & histology | Respiratory System--anatomy & histology | Respiratory Physiological Phenomena Classification: LCC RC424.7 (print) | LCC RC424.7 (ebook) | NLM WV 501 | DDC 616.85/5--dc23/eng/20230612 LC record available at https://lccn.loc.gov/2023022249 LC ebook record available at https://lccn.loc.gov/2023022250 NOTICE TO THE USER Care has been taken to confirm the accuracy of the indications, procedures, drug dosages, and diagnosis and remediation protocols presented in this book and to ensure that they conform to the practices of the general medical and health services communities. However, the authors, editors, and publisher are not responsible for errors or omissions or for any consequences from application of the information in this book and make no warranty, expressed or implied, with respect to the currency, completeness, or accuracy of the contents of the publication. The diagnostic and remediation protocols and the medications described do not necessarily have specific approval by the Food and Drug administration for use in the disorders and/or diseases and dosages for which they are recommended. Application of this information in a particular situation remains the professional responsibility of the practitioner. Because standards of practice and usage change, it is the responsibility of the practitioner to keep abreast of revised recommendations, dosages, and procedures.

Brief Contents 1 Introduction 2 Anatomy of Respiration 3 Physiology of Respiration 4 Anatomy of Phonation 5 Physiology of Phonation 6 Anatomy of Articulation, Swallowing, and Resonance 7 Physiology of Articulation and Resonance 8 Physiology of Swallowing 9 Anatomy of Hearing 10 Physiology of Hearing and Balance 11 Neuroanatomy and Neurophysiology:  Part 1 2 Neuroanatomy and Neurophysiology:  Part 2 1

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1 47 107 133 167 193 265 287 315 337 369 393

Contents

Preface xiii Acknowledgments xv



1 Introduction



2 Anatomy of Respiration

1

Key Terms 1 Biology 1 Anatomy 2 Physiology 4 Anatomical Nomenclature 4 Anatomical Orientation 5 Anatomical Terms 5 Body Systems That Support Speech, Language, and Hearing 9 Cell 9 Tissues 10 Joints or Articulations 24 Organs 27 Systems 27 Cranial Nerves 32 Olfactory 33 Optic 34 Oculomotor 36 Trochlear 36 Trigeminal 36 Abducens 37 Facial 37 Vestibulocochlear 38 Glossopharyngeal 39 Vagus 40 Accessory 42 Hypoglossal 42 Chapter Summary 43 References 45 Introduction to Respiration The Skeletal Framework for Respiration The Bony Thorax The Visceral Thorax vii

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47 49 49 64

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Respiratory Passages 64 Lungs 69 Respiratory Tissue and Gas Exchange 72 Muscles of Respiration 74 Patterns of Muscular Use in Respiration 75 Categorization of Muscles of Respiration 75 Primary Muscle of Inspiration 76 Accessory Muscles of Inspiration 78 Muscles of Expiration 92 Chapter Summary 102 Reference 105



3 Physiology of Respiration

107



4 Anatomy of Phonation

133



5 Physiology of Phonation

167

Introduction to Physiology of Respiration 107 Forces of Respiration 111 Active Force of Respiration 111 Passive Forces of Respiration 111 Pressures Involved in Respiration 112 Physics of Respiration/Breathing 113 Understanding the Mechanical Cycle of Respiration 116 Quiet Respiration:  Quiet Inspiration/Passive Expiration 116 Forced Respiration:  Forced Inspiration/Forced Expiration 117 Lung Volumes and Capacities 117 Changes in Respiration With Advanced Age 120 Measurement of Respiration and Instrumentation 120 Measuring Rate 121 Measuring Pressure 121 Measuring Lung Volumes and Respiratory Capacities 122 Process of Gas Exchange 125 Chapter Summary 129 References 132 Introduction 133 Larynx 138 Cartilages of the Larynx 138 Membranes and Ligaments 146 Muscles of the Larynx 149 Chapter Summary 163 References 164 Nonspeech (Biological) Functions 167 Breathing 168 Abdominal and Thoracic Fixation 168 Protection During the Swallow Reflex 168 Throat Clearing and Coughing 168 viii

Contents

Phonation 168 Coordinative Structures of Voice 169 Theories of Phonation 170 Myoelastic-Aerodynamic Theory 170 Body-Cover Theory 172 Nonlinear Source-Filter Coupling Theory 173 Parameters of Voice 174 Elasticity, Stiffness, and Inertia 174 Acoustic Parameters 174 Amplitude and Intensity 179 Aerodynamic Parameters 180 Variations in Vocal Fold Closure Patterns, Mucosal Wave, and Periodicity 182 of Vibration Vocal Fold Closure 182 Movement of the Mucosal Wave 184 Regularity and Periodicity of Vibration 185 Vocal Register 186 Sustained Phonation and Attack 188 Linguistic Aspects of Phonation 188 Chapter Summary 189 References 191



6 Anatomy of Articulation, Swallowing, and Resonance

193

Introduction 194 Bones of the Face 194 Mandible 194 Maxillae 196 Anatomy of the Hard Palate 197 Zygomatic Bones 200 Nasal Bones 200 Palatine Bones 201 Inferior Nasal Conchae 201 Vomer 203 Lacrimal Bone 203 Bones of the Skull 204 Ethmoid 204 Frontal Bone 206 Parietal Bones 206 Temporal Bones 207 Occipital Bone 208 Sphenoid 209 Muscles of the Face 210 Orbicularis Oris 213 Transverse Muscles 214 Elevators 217 Depressors 221 Parallel Muscles: Incisivus Labii Superior and the Incisivus Labii Inferior 224 ix

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Supplementary Muscles of Facial Expression 224 Cavities of the Vocal Tract 226 The Oral Cavity 226 Buccal Cavities 237 Nasal Cavity 238 Pharynx 238 Muscles of the Tongue 239 Intrinsic Muscles of the Tongue 239 Extrinsic Muscles of the Tongue 241 Muscles of Mastication 246 Masseter (Figures 6–58 and 6–59) 246 Temporalis (Figures 6–58 and 6–60) 247 Medial Pterygoid (Figure 6–61) 247 Lateral Pterygoid (Figure 6–62) 249 Digastricus (Figures 6–58 and 6–63) 250 Mylohyoid (Figures 6–58 and 6–64) 251 Geniohyoid (Figures 6–53 and 6–58) 251 Platysma (Figure 6–34) 252 Muscles of the Velum 252 Elevators of the Velum 253 Depressors of the Velum 254 Muscles of the Pharynx 255 Pharyngeal Constrictors 255 Longitudinal Muscles of the Pharynx 259 Chapter Summary 262 References 264



7 Physiology of Articulation and Resonance

265



8 Physiology of Swallowing

287

Introduction to Articulation and Resonance 266 Physiology of Articulation and Resonance 266 Role of the Lips in Articulation 266 Role of the Tongue in Articulation 268 Role of the Muscles of the Tongue in Articulation 268 Role of the Tongue in Consonant Production 269 Role of the Tongue in Vowel Production 269 Role of the Teeth in Articulation 275 Role of the Mandible in Articulation 276 Role of Cheeks in Articulation and Resonance 279 Role of Velum in Articulation and Resonance 279 Role of the Pharynx in Articulation 282 Chapter Summary 284 References 285 Introduction to Swallowing Process of Mastication and Deglutition Oral Preparatory Stage Described x

287 287 289

Contents

Oral Stage Described 291 Pharyngeal Stage Described 293 Esophageal Stage Described 297 Instrumentation 302 Videofluoroscopic Swallow Study/Modified Barium Swallow 302 Fiberoptic Endoscopic Evaluation of Swallow 303 High-Resolution Manometry 304 Changes With Age 305 Childhood Development 305 Changes With Normal Aging 307 Coordination of Respiration and Deglutition 309 Chapter Summary 309 References 312



9 Anatomy of Hearing

315

Structures of the Auditory Mechanism 315 Outer Ear 316 Auricle 316 External Auditory Meatus 318 Tympanic Membrane 319 Middle Ear 321 Ossicles 321 Muscles of the Middle Ear 324 Landmarks of the Middle Ear Cavity 325 Inner Ear 326 Auditory System:  Cochlea and Related Structures 327 Vestibular System 331 Vestibulocochlear Nerve (CN VIII) 332 Changes With Age (Presbycusis) 333 Chapter Summary 334 References 335

10 Physiology of Hearing and Balance



337

Properties of Sound 338 Physiology of the Outer Ear 340 Pinna and External Auditory Meatus 340 Physiology of the Middle Ear 341 Movement of the Tympanic Membrane and the Ossicular Chain 341 Eustachian Tube 344 Physiology of the Inner Ear 345 Stimulation of the Cochlea 345 Transduction 348 Auditory Central Nervous System 351 Afferent Pathway 352 Efferent Pathway 353 Auditory Cortex:  Auditory Processing and Speech Perception 353 Vestibular System 354 xi

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Instrumentation 355 Otoscopy 355 Pure Tone Audiometry 356 Speech Reception Threshold 357 Tympanometry 358 Acoustic Reflex Testing 358 Otoacoustic Emissions 359 Auditory Brainstem Response 360 Electrocochleography 360 Types of Hearing Loss 361 Conductive Hearing Loss 362 Sensorineural Hearing Loss 363 Mixed Hearing Loss 364 Chapter Summary 365 References 366

11 Neuroanatomy and Neurophysiology:  Part 1

369

12 Neuroanatomy and Neurophysiology:  Part 2

393





Cells of the Nervous System 369 Neurons 370 Neuroglia 372 The Central Nervous System 375 The Brain 375 Chapter Summary 388 References 390 The Lobes of the Cerebral Hemispheres 393 Frontal Lobes 394 Parietal Lobes 395 Temporal Lobes 396 The Occipital Lobes 398 Subcortical Structures 399 The Brainstem 399 The Cerebellum 402 The Thalamus 405 The Basal Ganglia 406 The Limbic System 408 The Spinal Cord 410 Blood Supply to the Brain 411 The Peripheral Nervous System 414 The Spinal Nerves 414 Chapter Summary 416 References 419

Glossary 421 Index 455

xii

Preface

It is with great pleasure that we introduce our new anatomy and physiology textbook for undergraduate programs in communication sciences and disorders. This book is the result of our passion for education and our commitment to the field of speech-language pathology and audiology. We are confident that this book will transform the way students learn anatomy and physiology. The inspiration for this book came from our experience with the Anatomage Virtual Dissection Table, which allowed us to view highresolution images from virtual cadavers and propelled us to take on this project. Before we embarked on this mission, we conducted a study with freshmen who had no prior class experience of anatomy and physiology related to speech-language pathology and found that the use of virtual dissection significantly improved their performance in tests and their understanding of anatomy. Encouraged by these results, we decided to write this textbook, which is filled with images from real cadavers, digitized and colored to target specific areas of the human body. With our experience teaching the new generation of students, we have found that the majority of students skim through their anatomy textbooks because they are unable to process the vast amounts of information in paragraph form. Many students have mentioned that they struggle with integrating, synthesizing, and comprehending the information presented in paragraph form — resulting in a lack of retention of material and a resultant decreased performance on examinations and tests. Students today tend to break down paragraphs into bullet form for processing and consumption of the material and then integrate the details together visually using images. This generation of students is also technology dependent; therefore, we listened to them and decided to write this book to make the learning process enjoyable for them. This text includes all the details of a traditional anatomy and physiology textbook but with unique pedagogical features to enhance the learning process. Our approach is image-heavy and includes a majority of high-resolution pictures from real cadavers. We introduce each topic in paragraph form, followed by information presented primarily in bullet form, which caters to the emerging needs of these students who spend vast amounts of time creating bulleted study guides. Immediate access to digital illustrative content that will supplement and enhance the students’ understanding of the primary information is also provided adjacent to each topic. The book includes box features, key terms, chapter objectives, and chapter summaries. The book comes with online ancillary materials for instructors and students. The student site includes interactive quizzes, vocabulary flashcards, a searchable image bank, and study guides. Instructors can download PowerPoint slides, a test bank, and an image bank, and can also access all of the student materials. We are proud to say that this textbook is unlike other traditional anatomy and physiology textbooks. Professors who adopt it will immediately notice the difference. We are confident that our approach will boost student engagement and retention of material, leading to increased performance on examinations and tests. Our goal is to provide students with a comprehensive understanding of the human body and how it relates to communication disorders.

xiii

Acknowledgments

An enormous undertaking of this nature would not be possible without the help of our students, colleagues, and publisher. We would like to especially thank Valerie Johns, the executive editor at Plural Publishing, Kaitlin Nadal the project editor, Jessica Bristow the production editor, Lori Asbury the production manager, and the rest of the team at Plural Publishing. We are so thankful for their attention to detail, enthusiasm, and dedication to see this book come to fruition. We are deeply grateful to Alexandra Woodward, Alyssa Robinson, Ashley Pitz, Ava Venuto, Brooke Penrod, Emily Magrini, Faith Foster, Jillian Scanlon, Julia Regnault, Madison Pachucy, Maria Monteleone, Megan Aaron, Megan Fenstermaker, Megan Roman, Quinn Kelley, Samantha Buldo, Samantha Delmar, and many others who spent countless hours creating the images for this book. We would like to thank them for their invaluable efforts. We also thank Thomas Carroll and Erin Roberts for the images they contributed. Finally, a special thanks to Eileen Tellis for the wonderful images she created for this book as well as the Anatomage company for allowing us to use their images in this book. We also thank our families for their unconditional love and support. We hope that this textbook will open doors to those very deserving individuals who have dedicated their lives to serving persons with communication disorders. We invite you to explore our book and learn from it. It is our sincere hope that it will inspire you to continue your education and your pursuit of excellence in the field of speech-language pathology.

xv

1 Introduction

➤ Learning Objectives Upon completion of this chapter, students will be able to: n

Understand foundational information about human anatomy and physiology and the use of anatomical nomenclature, orientation, and terms.

n

Learn organs and systems of the human body, how they function, and their effects on speech, language, swallowing, cognitive, and hearing abilities.

n

Understand the function of the 12 pairs of cranial nerves and how damage to these nerves can impact physiology.

➤ Key Terms Biology The term biology originates from the Greek word Bios which means “life.” Biology is the study of living organisms. There are many specialty areas that fall under biology. These include cell biology, evolutionary biology, molecular biology, biochemistry, physiology, zoology, genetics, botany, and ecology. There is a great deal of overlap within these fields. Biology includes several constant factors: the study of evolution, heredity, consumption of energy, equilibrium, and cell theory. The human biological makeup includes cells, tissues, joints, organs, and systems. Cell structures are the basic units of the organism and are the building blocks of life. Tissues comprise many similar cells that are responsible for a particular function. Organs are formed by grouping several tissues. A biological system is a network or a group of two or more organs that combine to function together. Joints are where two bones are attached to allow body parts to move. 1

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Anatomy Anatomy is a branch of biology that studies the structures of organisms and their parts. Anatomy deals with dissection (e.g., human cadavers). The term cadaver is derived from the Latin verb — cadere, which means corpse. Anatomy has two divisions. The first is macroscopic anatomy or gross anatomy that uses unaided eyesight to study parts of an animal’s body. Gross anatomy also includes superficial anatomy. Initially, human anatomy was studied by superficially examining the wounds that soldiers sustained during war. Doctors later began to dissect bodies of dead soldiers to determine the cause of death. In the process of dissection, physicians were able to observe the relationships between body parts. In time, a second division of anatomy evolved — microscopic anatomy. This type of anatomy allows clinicians to use optical methods to observe structures and tissues inside a living person without dissection. Microscopic anatomy includes histology, which is the study of tissues under a light or electron microscope, and cytology, which is the study of cell structures and functions. Within the field of anatomy, several specializations (Figure 1–1) have evolved: n

Developmental anatomy, also called embryology, studies how an embryo develops from a single cell to evolve into a human being. Embryology includes the study of prenatal and postnatal developmental changes and the processes by which these changes occur.

n

Surface anatomy, also called superficial anatomy, topographic anatomy, or regional anatomy, studies the surfaces of human body structures. Surface anatomy is important for surgical procedures because it helps doctors identify the position of internal organs from the surface of the body. It establishes a relationship between deeper (internal) organs of the body and the surface of the body.

n

Comparative anatomy is the study of similarities and differences in the structures of all living organisms. A comparative anatomist can study and compare the bones of humans, birds, chimpanzees, and frogs to look for similarities and differences to determine if various organisms share a common ancestor. Comparative anatomy also helps with classification of anatomical structures of organisms based on similarities. Comparative anatomy is mainly used in the field of paleontology (the study of animal and plant fossils).

n

General anatomy is the study of gross and microscopic structures including different parts of the body, its fluids, and its tissues.

n

Descriptive anatomy or systematic anatomy is the study of organ systems (e.g., respiratory system) that work together.

n

Applied anatomy is also called clinical or practical anatomy. It is mainly concerned with the diagnosis and treatment of various conditions as well as the application of anatomical knowledge to specific fields (e.g., surgery).

n

Radiological anatomy uses fluorography and radiography to study anatomy (e.g., x-rays).

n

Morbid anatomy, also called pathological anatomy, is the study of diseased tissues.

Anatomical variation indicates that there are nonpathological structural anomalies that are different from normal. These differences do not indicate that there is any particular disorder. When looking more carefully at any given species, it should be noted that there is great variation between specimens. This variation does not necessarily mean that there will be differences in function. If there is a detrimental effect on functioning, then treatment may be required to rectify the impairment. 2

3

FIGURE 1–1.  Specializations in anatomy.

Introduction

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Physiology Physiology is a subdiscipline of biology and includes the study of the functions of living organisms and their parts. Physiology examines how organs, organ systems, organisms, cells, and biomolecules carry out the chemical processes that are inherent in a living organism. One way of studying physiology is to use electroencephalography (EEG) to record electrophysiological activity in the brain. Electrodes are placed on the scalp, and voltage changes in the neurons of the brain can be measured. EEG is often used to diagnose sleep disorders, epilepsy, and other conditions as the EEG readings can show anomalies in brain waves. Hippocrates, the father of medicine, is credited with discussing human physiology as far back as the fourth century bc. Claudius Galenus (ad 130–200), the founder of experimental physiology, was the first to document his experiments to examine the functions of the body; however, Jean Fernel (1497–1558) introduced the term physiology. Physiology is divided into the following specialties: n

Plant physiology is a branch of botany. Plant physiologists study the functioning of plants, including respiration, nutrition, photosynthesis, germination, circadian rhythms, and other processes. n Microbial physiology includes the study of bacteria, parasites, viruses, and fungi. It is used in the fields of metabolic engineering and functional genomics. n Cellular physiology is the examination of factors that are responsible for keeping a cell alive (e.g., water in the roots of a plant). n Animal physiology is the study of life-supporting processes, functions, and properties of blood flow, genetics, biological structure, regulation of temperature, and hormones in animals and humans. n Viral physiology is the study of viruses.

Anatomical Nomenclature For centuries, those involved in the study of anatomy tried to develop a uniform method of assigning names to anatomical structures. By the late 19th century, there were over 50,000 terms for the parts of the body. What became confusing at times is that the same structures were called different names. Some of this confusion stemmed from the words that were derived from Latin or Greek origin or from where the anatomist was educated or country of origin. In 1895, anatomists were interested in creating an international system of anatomical terminology and agreed on the Basle Nomina Anatomica (BNA). The result of this agreement was that the number of anatomical terms was reduced to 5,528. In 1955, the BNA was revised and updated, and the name was changed to Nomina Anatomica. Around 1985, there were some disagreements about terminology between the International Anatomical Nomenclature Committee and the International Federation of Associations of Anatomists (IFAA); therefore, in 1998, a new, simplified, updated, and uniform anatomical terminology was agreed upon by the IFAA that created a new committee, the Federative

4

n

Introduction

Committee on Anatomical Terminology and introduced the term Terminologia Anatomica (TA). It is considered the international standard for anatomical terminology. Gray’s Anatomy (2005) specifically recognizes TA (Standring, 2005).

Anatomical Orientation To study the spatial relationships that exist in the human body, it is necessary to have a point of reference when discussing organs, bones, muscles, nerves, and other structures. The axial skeleton (Figure 1–2) comprises the bones of the trunk and the head. In humans, the axial skeleton consists of 80 bones (vertebral column, hyoid bone, skull bones, rib cage, sternum, and ossicles of the middle ear). The entire human skeleton includes the axial skeleton and the appendicular skeleton (126 bones) (Figure 1–3). The word appendicular is derived from appendage (joined to something). The appendicular skeleton includes the limbs as well as the skeletal structures in the limbs, the pelvic girdles, and the pectoral girdles (also known as the shoulder girdles) — these form the complete skeleton (White et al., 2012). This point of reference is the standard anatomical position where the body is at rest and standing erect with the feet together or slightly apart. The face is directed forward. The arms are at the side and rotated outward, with the palms facing forward. The thumbs are pointed away from the body (Tortora & Derrickson, 2006).

Anatomical Terms Contrasting pairs of terms for common locations and for anatomical surfaces are listed next and displayed in Table 1–1 and Figure 1–4.

FIGURE 1–2.  Axial skeleton. Reproduced with permission from Anatomage.

5

Introduction

1

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 1–3.  Appendicular skeleton. Reproduced with permission from Anatomage.

6

TABLE 1–1.

n

Introduction

Contrasting Pairs of Terms

Anterior (ventral) — front of the body (away from the back)

Posterior (dorsal) — back of the body (away from the front)

Adduction — moving toward the midline

Abduction — moving away from the midline

Agonists — muscles that can cause movement because of their own contraction

Antagonists — muscles that oppose a particular movement

Central — situated at the center

Peripheral — situated at the edge

Contralateral — opposite side

Ipsilateral — same side

Dorsal — away from the front of the body

Ventral — toward the front of the body

Endo — inner

Ecto — outer

Flexion — bending of a body part

Extension — straightening of a body part

Inferior — below another body part

Superior — above another body part

Infra — below

Supra — above

Internal (deep) — inside

External (superficial) — outside

Intrinsic — within the organ

Extrinsic — from the outside

Ipsilateral — affecting the same side of the body as the site of the lesion

Contralateral — affecting the opposite side of the body from the site of the lesion

Medial — closer to the axis or midline

Lateral — away from the axis or midline

Prone — lying flat, facedown

Supine — lying face upward

Protraction — moving a body part forward (jutting out the chin)

Retraction — pulling a body part backward (pulling the chin in)

Proximal — near to the center of the body

Distal — away from the center of the body

Rostral (cranial) — toward the nose, mouth, and head (usually refers to the structures in the cranium)

Caudal — posterior of the body (toward the tailbone)

Superficial — toward the surface of the body

Deep — away from the surface of the body

The human body has axes (singular axis) or midlines that give rise to other structures. These are two-dimensional sections of the body. There are three main planes (axes) of the body. These planes are imaginary two-dimensional surfaces that pass through the body (Figure 1–5). The sagittal/vertical plane divides the body into right and left sides vertically. It is named after the sagittal suture that runs from the front to the back of the top of the skull. If this plane courses down the middle of the body, it is called the median or midsagittal plane; however, it is known as the longitudinal section or parasagittal plane if it divides the body into unequal right and left sides. The frontal/coronal plane divides the body into ventral/anterior (belly) and dorsal/posterior (back). It is named after the coronal suture that separates the frontal and parietal bones of the skull. This is a longitudinal plane because it is perpendicular to the transverse plane. 7

Introduction

1

FIGURE 1–4.  Planes (axes) of reference and anatomical terms.

A

B

C

D

FIGURE 1–5. A. Sagittal/frontal/horizontal plane. B. Sagittal/vertical plane. C. Frontal/coronal plane. D. Horizontal plane. A–D reproduced with permission from Anatomage.

8

n

Introduction

The transverse/horizontal/axial/transaxial plane divides the body into upper and lower parts. It is perpendicular to the sagittal and coronal planes and is often used to describe the location of parts of the body in relation to one another.

➤ Body Systems That Support Speech, Language, and Hearing Cell Cells are basic structures of all living organisms. They are the smallest units of life and are often referred to as “the building blocks of life.” Humans have trillions of cells that specialize in different functions. Cells evolve from one generation to the next. Nutrients from food are absorbed into the cell to carry out several functions. Each cell contains structures called organelles that are responsible for tasks such as creating proteins to generate energy for the cell. Cells have a finite life span. Red blood cells only live for 100 to 120 days; however, it takes about 2 days for bone marrow to make a new red blood cell, with approximately two million new ones produced every second (Sackmann, 1995). The term cell was coined in 1665 by Robert Hooke, an English philosopher, architect, and polymath (Hooke, 1665). In 1839, Matthias Jakob Schleiden, a German botanist, and Theodor Schwann, a German physiologist, cofounded cell theory. The cell (Figure 1–6) has several parts: n

Cytoplasm (protoplasm) is part of a living cell. It is composed of jellylike fluid (cytosol). It is surrounded by plasma membrane. Cytoplasm is made up of about 80% water and 20% protein.

n

Cytoskeleton is a network of long fibers that is the structural framework of the cell. The cytoskeleton is responsible for cell division and movement.

n

Endoplasmic reticulum is an organelle that moves molecules within and outside a cell.

n

Extracellular fluid is fluid in the spaces outside the cell.

n The

Golgi apparatus receives molecules that have been sent from the endoplasmic reticulum, packages them, and sends them out of the cell.

n

Intracellular fluid resides inside the cell.

n

Lysosomes and peroxisomes are organelles. They are known as the “recycling center” or “repair shop” of the cell. When bacteria enter the cell, they clean the cell of toxic material and recycle cell parts that are damaged.

n

Mitochondria are organelles that can make duplicates of themselves. These organelles can convert energy from food for the cell to use.

n

Nucleus is the center of the cell. It is the brain trust of the cell and controls the functioning of the cell. It informs the cell to grow, separate, or die. Deoxyribonucleic acid (DNA), the cell’s hereditary material, is located in the nucleus. The nucleus is covered by a membrane that protects DNA and separates it from the remainder of the cell. Within the nucleus is the genome (the genetic material of an organism). 9

Introduction

1

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 1–6. Cell.

n

Plasma membrane is the outer layer of the cell. It controls what materials enter and exit the cell.

n

Ribosomes are organelles that provide the cells with genetic orders to make proteins. They can either be connected to the endoplasmic reticulum or float in the cytoplasm.

A group of cells together form tissues. When tissues group together, they form organs (e.g., lungs, brain, kidneys, etc.).

Tissues Tissues (Figures 1–7 and 1–8) are colonies of cells that are similar in structure and function. There are four basic types of tissues. These are epithelial, connective, muscular, and nervous.

Epithelial Epithelial tissues cover the outer surface as well as the internal passages and cavities of the body. They line the blood vessels and organs throughout the body. The lung alveoli and the lining of the mouth are where epithelial tissue can be found as well as in many other locations. If an injury occurs on the surface of the body, it results in drying of the skin; however, in crevices of the body where there is limited friction, these tissues form smooth surfaces. An interesting aspect about epithelial tissues is that they may have short hairlike structures (i.e., cilia) that move material over the cell surface. Epithelial tissues rest on connective tissue or basement membrane — which acts as a framework on which epithelium can grow

10

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FIGURE 1–7.  Tissues. Reproduced with permission from Anatomage.

and revive after injuries (McConnell & Thomas, 2006). The basement membrane is porous; however, it decides which substances can enter the epithelium. Epithelial tissue (Table 1–2) can be squamous, columnar, or cuboidal. Functions of epithelial tissues: n

Sensory — sensory nerves in the tongue, ears, and nose provide sensation.

n

Absorptive — in the intestines, they absorb nutrients during digestion.

n

Protective — a defense mechanism against physical trauma, radiation, and toxins. The skin is the initial barrier against bacteria and viruses.

11

12

FIGURE 1–8.  Tissue chart.

TABLE 1–2.

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Epithelial Tissue

Type

Shape

Location

Squamous

Flat

Found in alveoli of the lungs or the lining of the skin surface

Columnar

Oblong

Forms the lining of the intestines and stomach

Cuboidal

Cube shaped

Found in kidney tubules or pancreas

n

Glandular — there are two types: (a) endocrine — secrete enzymes and hormones into the extracellular space and are absorbed by the vascular system, and (b) exocrine — secrete material into a duct that subsequently sends the material to the lumen of an organ.

n

Secretory — secretion of hormones into the vascular system or the secretion of mucus and sweat that are delivered by ducts.

Connective These tissues are found everywhere in the body as well as between other tissues. In the central nervous system (CNS), the meninges (the outermost membranes) (Figure 1–9) that cover the brain and spinal cord are made up of connective tissue. Connective tissues bind structures together and have very few cells. They have large quantities of extracellular substance called the matrix. Ground substance and fibers create the matrix for connective tissue. About 1 in 10 people have connective tissue disorder. Marfan syndrome, for example, is a connective tissue disorder that affects the eyes, heart, bones, ligaments, and blood vessels. These individuals are usually tall and have long bones and thin toes and

FIGURE 1–9.  The meninges.

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Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

fingers. Osteogenesis imperfecta is another connective tissue disorder that results in fragile bones, lax ligaments and joints, and low muscle mass. Those affected may present with a curved spine, hearing loss, breathing difficulties, and teeth that easily break. Other types of connective tissue disorders include rheumatoid arthritis. In this condition, the immune system attacks the synovium (a thin membrane that lines the joints), resulting in swelling of the joints, pain, and stiffness. Symptoms include fever, appetite loss, and fatigue. Connective tissue has three parts — fibers, fibers ground substance, substance and cells cells: n

Fibers are of three types, collagenous, elastic, and reticular. Collagenous fibers bind bones to each other. Collagen is derived from the Greek word “glue.” These fibers are located in the cornea, cartilage, ligaments, tendons, skin, and blood vessels. Collagen is the most plentiful protein in the body. Collagen tissues may be compliant (tendon), rigid (bone), or a mix of compliant and rigid (cartilage). A fascia, for example, is a sheet of connective tissue that is mainly made up of collagen. It is located just below the skin and joins and steadies, encloses, and separates muscles and other organs. Elastic fibers allow the lungs and arteries to shrink and expand. They are located in the extracellular matrix. Reticular fibers form a framework for other cells. They are found in the bone marrow and liver.

n

Ground substance is a colorless and sticky fluid that slows the spread of pathogens (anything that can cause disease).

n

Cells have several parts including adipocytes, fibroblasts, leukocytes, macrophages, and mast cells. Adipocytes contain an abundance of adipose material that is responsible for storing energy as fat. Fibroblasts play an important role in wound healing. Leukocytes are white blood cells that are produced in the bone marrow. They protect the immune system. Macrophages are of Greek origin (phagein, meaning “to eat”). These are a type of white blood cell that digests cancer cells, waste, and microbes. They stimulate the immune system and serve an anti-inflammatory role. Mast cells are white blood cells that are involved in wound healing and serve as a defense against pathogens (Polyzoidis et al., 2015).

Connective tissue can be subdivided into connective tissue proper and specialized connective tissue. tissue Connective Tissue Proper.  Connective tissue proper includes loose and dense connective tissue.

Loose connective tissue attaches epithelial tissue to other tissues and keeps the organs in place. These tissues surround nerves and blood vessels. Loose connective tissue includes areolar, reticular, and adipose tissue. Areolar tissue is a type of loose connective tissue that is found just under the skin. It is one of the most widely distributed tissues in the body. Reticular connective tissue is located in the spleen, bone marrow, kidney, and lymph nodes. Adipose tissue, also called body fat, stores energy in lipids. It acts to protect the body. It is an endocrine organ that produces hormones like estrogen (Kershaw & Flier, 2004). Dense connective tissue includes dense regular and dense irregular tissue. Dense regular tissue joins tissues in different parts of the body. These tissues have enormous strength. When ligaments and tendons are damaged, they heal slowly because the dense connective tissues have limited blood supply. Dense regular tissue includes white fibrous connective tissue and yellow fibrous connective tissue. White fibrous connective tissue is very strong; however, it is not elastic. Therefore, if the bone experiences an excessive force, the bone that it is connected to will break before the tissue tears. Yellow fibrous connective tissue is very elastic and is found in the vocal folds, trachea, bronchi, and larger arteries. Examples of white and yellow fibrous connective tissue include tendons, ligaments, and aponeurosis. Tendons are flexible bands of nonelastic fibrous connective tissue that attach a muscle to a bone. Tendons are composed of collagen and are viscoelastic in nature (elastic and viscous).

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The Achilles tendon (heel cord) is the thickest tendon in the human body and is located at the back of the leg. In Greek mythology, Achilles’s heel was his only point of vulnerability because his mother held him by one heel when she dipped him in the river to coat his body with magical invincibility. Because she only held Achilles by one heel, it was not protected by the coating — during his famous battle, the arrow was able to penetrate his heel. Ligaments are short bands of tough, flexible tissues that bind two bones or cartilage together. They also hold joints together. Ligaments are incapable of regenerating naturally; therefore, athletes who often tear the anterior cruciate ligament (ACL) require ACL surgery to replace the ligament with artificial material. A ligament that is specific to speech production is the cricothyroid ligament (Figure 1–10). Aponeuroses are flat-broad tendons that join muscles to bones or other muscles. They have limited nerves or blood supply. Dense irregular tissue is present in the deep layers of the skin, digestive tract, and lymph nodes. Specialized Connective Tissue.  Specialized connective tissue includes cartilage, bone, and blood.

Cartilage is smooth elastic tissue. Its function is to protect the bones at the joints. It also forms the structure of the ear, nose, rib cage, and bronchial tubes. Cartilage is not as supple as muscle and not as hard as bone. Cartilage does not contain nerves or blood vessels. For example, inflammation of the cartilage that connects the ribs to the sternum (breastbone) may result in costochondritis (chest wall pain). The pain that is caused by costochondritis may feel like a person is experiencing a heart attack. Another example of cartilage that is related to speech includes the cricoid (ring-shaped cartilage) cartilage (Figure 1–11). The main role of the cricoid cartilage is to connect other muscles, cartilage, and ligaments that are involved in adducting (closing) and abducting (opening) the vocal folds for speech production. Cartilage can be hyaline, elastic, or fibrous. Hyaline (gaslike) cartilage has an abundance of collagen and is located on the surface of many joints. It has no blood vessels or nerves. It is the most widespread form of cartilage. Elastic cartilage or yellow cartilage that can easily be bent is present in the external auditory meatus, outer ear, and epiglottis. The epiglottis acts as a valve that hangs over the entrance to the larynx and opens when a person breathes and closes during swallowing to prevent aspiration (Figure 1–12).

FIGURE 1–10.  Cricothyroid ligament — anterior view. Reproduced with permission from Anatomage.

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FIGURE 1–11.  Cricoid cartilage — anterior view. Reproduced with permission from Anatomage.

FIGURE 1–12.  Epiglottis — posterior view. Reproduced with permission from Anatomage.

Fibrous cartilage (fibrocartilage) is found in the temporomandibular joint (TMJ) (Figure 1–13). If hyaline cartilage is damaged, the blood supply from the underlying bone may start the healing process by forming a scar with fibrous cartilage. Bone is part of the vertebral skeleton and is the hardest structure of the body. Around the age of 20 years, bone mass reaches its maximum density. Bones enable the body to have structure and provide the body the ability to move. They are covered by a fibrous membrane called periosteum. Deep layers of periosteum comprise osteoblasts that help with forming new bones when there are fractures. Bones comprise all blood vessels, nerves, bone marrow, and epithelium. They function to protect the organs in the body and produce red and white blood cells. Bones are responsible for maintaining the pH levels in the body. At birth, the human body has 270 bones, but these decrease to 206 because some have fused together by the time a person reaches adulthood (Steele et al., 1988). The femur is the largest bone in the body, and the stapes (Figure 1–14) in the middle ear (Figure 1–15) is the smallest bone in the body. There are two types of bone tissue — cortical bone and cancellous bone. Cortical bone tissue (compact bone) comprises 80% of the weight of the skeleton and forms the hard outside part of the bone. It supports the body by enabling movement, storing and releasing calcium, and protecting organs. Cancellous bone tissue (spongy bone) is less dense than cortical bone tissue. It is weaker, softer, and suppler than 16

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FIGURE 1–13.  Temporomandibular joint. Reproduced with permission from Anatomage.

FIGURE 1–14. Stapes.

cortical bone tissue. It is vascular and produces and contains red bone marrow. These bones are found near the joints and at the ends of long bones. Blood delivers oxygen and nutrients to the cells and moves waste matter away from the cells. The heart pumps blood; this allows the blood to be carried around the body via blood vessels. Blood is made up of blood cells that are floating in blood plasma that comprise glucose, hormones, proteins, carbon dioxide, blood cells, and mineral ions. There are different types of blood cells, including red blood cells 17

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 1–15.  Anatomy of the ear. Reproduced with permission from Anatomage.

(erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). Red blood cells are the most profuse cells.

Muscular They are soft tissues that allow the muscles to contract. Muscles have different functions based on the location of the body; however, we would not be able to function without their presence as they allow the body to move bones, which allows the body to function. Muscles can be skeletal, smooth, and cardiac — these muscles are innervated by the nervous system (Figure 1–16). A motor unit is made up of a single motor neuron and all of the individual muscle fibers innervated by single motor neurons. There are more muscle fibers than motor neurons; therefore, individual motor axons course throughout the muscles uniformly to contract different muscle fibers in a single muscle uniformly. Muscles usually have an origin and a point of insertion. The origin is typically fixed and has less movement. The insertion is the point being acted on. For example, the cricopharyngeus muscle that originates on the lateral surface of the cricoid cartilage and inserts into the midline of the pharyngeal raphe constricts the pharyngeal cavity and the entrance to the esophagus. When muscles contract, they provide movement; however, muscles can apply force in only one direction. Muscles that permit movements are called prime movers (agonists), and muscles that provide stability are called fixators. For example, the four suprahyoid muscles (digastric, stylohyoid, geniohyoid, and mylohyoid) (Figure 1–17) that are located above the hyoid bone in the neck assist with raising the hyoid bone and opening the esophagus during swallowing. The stylohyoid raises and retracts the hyoid bone, thus lengthening the floor of the mouth while swallowing. Skeletal (striated) muscles contract voluntarily because of messages that are received from the CNS. These muscles are connected to the bones by tendons. Skeletal muscles are actually a bundle of 18

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FIGURE 1–16.  Cardiac, smooth, and skeletal muscles. Reproduced with permission from Anatomage.

FIGURE 1–17.  Suprahyoid muscles. Reproduced with permission from Anatomage.

cells called muscle fibers (fascicles; muscle cells). Muscle fibers are the smallest unit of muscle tissues, are covered by a fibrous tissue called endomysium that separates muscle fibers from each other, are made up of thousands of long filaments called myofibrils that contain actin (thick filaments) and myosin (thick filaments), and also contain myoglobin which is a protein that binds oxygen to muscle fiber. Groups of 19

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

muscle fibers are called fasciculi, and each fasciculus is covered by fibrous connective tissue called perimysium, which separates groups of muscle fibers from one another and permits the muscle to function as a single unit. A group of fasciculi is covered by connective tissue called epimysium. Each muscle, in turn, is covered with fascia, which is dense connective tissue. As a percentage of body mass, skeletal muscle comprises 42% of the weight of an average adult male and 36% of the weight of an average adult female (Marieb & Hoehn, 2007). There are two types of muscles — Type I and Type II (Figure 1–18): Type I muscles are slow twitch or slow oxidative. They have an abundance of mitochondria and myoglobin (similar to hemoglobin in the blood) that provide the muscle tissue with its red color and carry extra oxygen to maintain aerobic activity. It is typical for marathon runners to have more of these types of fibers, usually acquired through training and genetics. Type II muscles are fast-twitch or fast-oxidative fibers that result in varying degrees of contractile speed. n

Type IIa is loaded with capillaries and mitochondria, is aerobic, and is red in color. These are also called fast-twitch oxidative fibers and produce and divide adenosine triphosphate (ATP) quickly by using anaerobic and aerobic metabolism, which results in strong muscle contractions. ATP is needed to move chemical energy in the cells for muscle movement. Type IIa muscles are typically seen in middle-distance runners (e.g., 800 meters).

n

Type IIb are anaerobic muscles that look white because of less myoglobin and mitochondria. These are also called fast-twitch glycolytic fibers. They break down rapidly and manufacture ATP at a slower rate, resulting in short, quick bursts of power with fatigue occurring quickly. These muscle types are seen in sprinters (e.g., 100 meters).

Smooth (nonstriated) muscles contract involuntarily and may be triggered by endocrine or peripheral plexus activation or because of messages received by the CNS. Smooth muscles are innervated by

FIGURE 1–18.  Type I and II muscles.

20

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the autonomic nervous systems (ANS). These muscles are found in the stomach, uterus, blood vessels, esophagus, bronchi, and intestines. Smooth muscle can be single- or multiunit muscle. In the single-unit muscle, the entire muscle contracts or relaxes at once (e.g., blood vessels). The trachea, however, is a multiunit muscle. Smooth muscles are mainly made up of myosin and actin molecules that help with contracting the muscle. Myosin fastens to actin and ATP. Like smooth muscle, cardiac (semi-striated) muscles contract involuntarily and may be triggered by endocrine or peripheral plexus activation or because of messages received by the CNS. When the cardiac muscles in the heart contract, blood is sent out of the ventricles and the atria to blood vessels into the circulatory system.

Nervous Nervous tissue is the primary component of the brain and spinal cord of the CNS and the peripheral nerves of the peripheral nervous system (PNS) (Figure 1–19). The CNS includes the brain and spinal cord, and the PNS mainly comprises nerves (Figure 1–20). Cranial nerves arise from the brain and brainstem, whereas spinal nerves emerge from the spinal cord. The skull protects the brain, and the vertebrae protect the spinal cord. The CNS is covered and protected by an outer layer called the meninges. The meninges comprise the dura mater, pia mater, and arachnoid mater. Cerebrospinal fluid is present in the space between the pia mater and the arachnoid mater. This space is called the subarachnoid space. The PNS is further divided into the somatic nervous system and ANS. The ANS is mainly involuntary and includes the sympathetic (associated with “fight-or-flight” reaction and is active during stressful situations; it regulates skin conductance), parasympathetic (associated with physiological states that promote growth, restoration, and repair), and enteric (associated with pancreas, gallbladder, and gastrointestinal functioning) nervous systems. The average adult brain weighs about 3 pounds and has approximately 100 billion neurons and trillions of glial cells. Neurons (Figure 1–21) and glial cells are the two main types of cells. Nervous tissue includes neurons (send and receive information) and neuroglia (glial cells) which transmit nerve impulses, provide nutrients, support the neuron, electrically insulate neurons, and remove dead neurons. They hold the neuron in place like glue. Glial cells include oligodendrocytes (in the CNS) and Schwann cells (in the PNS) (Figure 1–21). These cells create myelin (layers of a fatty substance) (Figure 1–21). Information is transmitted via neurotransmitters (chemical) and action potentials (electric). Nervous tissue has different kinds of nerve cells. All nerve cells have axons (transmit electrical impulse away from the cell neuron’s body) that send action potential signals (short moments where electrical signals of a cell elevate and fall) to the adjoining neuron at junctions called synapses (Figure 1–21). Myelin covers axons and provides electrical insulation that allows them to transmit action potentials. Groups of axons bundle together to form nerves. These nerves can be motor (efferent), sensory (afferent), or mixed (serve both functions). Motor nerves transmit signals from the brain to other parts of the body, and sensory nerves transmit information from the body to the CNS. The CNS is made up of gray matter and white matter. Gray matter is found in the brain, cerebellum, brainstem, and spinal cord. It is made up of capillaries, glial cells, dendrites, axons, synapses, and neuronal cell bodies. Gray matter has many cell bodies but limited myelinated axon tracts (Purves et al., 2008). The difference in color between gray and white matter occurs because of how white the myelin appears (Kolb & Whishaw, 2003). Most of the neuronal cell bodies contain gray matter that is involved in hearing, speech, emotions, muscle control, and sensory perception. White matter is made up of myelinated axons that are also called tracts. Myelin permits the electrical signal to be sent efficiently and rapidly, thereby increasing the speed at which nerve signals are transmitted (Klein & Thorne, 2007). 21

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22

FIGURE 1–19.  Nervous system.

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FIGURE 1–20.  Central and peripheral nervous systems. Reproduced with permission from Anatomage.

FIGURE 1–21. Neuron.

White matter has few cell bodies and mainly comprises long-range myelinated axon tracts (Blumenfeld, 2010). White matter is located in the deep parts of the brain and the outer parts of the spinal cord. It controls the dispersal of action potentials and relays and coordinates message transmission to different parts of the brain. The largest amount of white matter can be found in the corpus callosum (Schüz & Braitenberg, 2002) (Figure 1–22). The corpus callosum connects the two cerebral hemispheres and permits the two hemispheres to communicate. Multiple sclerosis, though rare, is one of the most 23

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

common white matter diseases. In multiple sclerosis, the myelin sheath that surrounds the axons gets inflamed and eventually dies.

Joints or Articulations A joint is a place where two bones are attached to allow body parts to move. Joints are usually composed of fibrous connective tissue and cartilage. Joints allow for different kinds of movement. Some joints allow very limited movement (e.g., sutures between the bones of the skull have very little movement to protect the brain), while other joints have more movement (e.g., the knee, elbow, etc.) to allow them to lift heavy loads. A suture (Figure 1–23) is a fibrous joint that is only located in the skull.

FIGURE 1–22.  Corpus callosum. Reproduced with permission from Anatomage.

FIGURE 1–23.  Sutures. Reproduced with permission from Anatomage.

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Joints are classified based on how the bones connect to each other (structural classification) or by the amount of movement between the bones (functional classification). Structural Classification (binding): (binding):  There are three structural classifications of joints including fibrous, cartilaginous, and synovial. Fibrous joints are connected by dense regular connective tissues that have an abundance of collagen fibers. Cartilaginous joints are attached by cartilage. Synovial joints are not directly attached but are bonded by dense irregular connective tissue. Functional Classification (movement):  (movement): There are three functional classifications of joints including synarthrodial, amphiarthrodial, and diarthrodial or synovial. Synarthrodial joints allow minimum or no movement. Most of these joints are fibrous (e.g., skull sutures). They are further subdivided into sutures, schindylesis, gomphosis, and syndesmosis: Suture or seam is found only in the skull. These are immovable joints that occur between the bones of the skull. There are three types of suture — sutura dentata, sutura serrata, and sutura limbosa: n Sutura dentata is a toothlike fibrous joint that interlocks along the margins of the bones of the skull. n Sutura serrata is a fibrous joint where connecting bones interlock along serrated edges and look like fine-tooth saws. n Sutura limbosa is a fibrous joint with serrated edges of connecting bones of the skull (e.g., the parietal and temporal bones interlock). Schindylesis, also called a “wedge-and-groove” joint, occurs when the crest of one bone is connected to the groove of another bone. This joint is located between the vomer and the perpendicular plate of the ethmoid bone. Gomphosis is a joint that is found between the root of the teeth and the socket of the mandible (jawbone). The movement of the gomphosis is limited; however, movement can occur when braces are used to readjust teeth. Syndesmosis is a minimally movable joint. When someone injures an ankle syndesmosis, it is also called a “high ankle sprain.” Amphiarthrodial  joints allow some movement. Most of these joints are cartilaginous (e.g., intervertebral discs). There are two types of amphiarthrodial joints — synchondrosis and symphysis: Synchondrosis (Figure 1–24) is a term that is used when hyaline cartilage is the connecting method. An example of a synchondrosis joint is when the first rib in the body joins the manubrium (the broad upper part of the sternum). This joint ossifies with age. Symphysis (Figure 1–25) occurs when there is a fibrocartilaginous merging of two bones. In the facial skeleton, the mandible is where the two lateral halves of the jawbone are fused together. Diarthrodial/synovial  joints (Figure 1–26) move freely. These joints are covered by an outer band of fibrous tissue called the articular capsule that holds the bones together and an inner layer called the synovial membrane that encloses synovial fluid that lubricates the joint cavity. Arthritis is a disorder that affects the joints and is a leading cause of disability in older people. Symptoms include stiffness and pain in the joints. Osteoarthritis is the most common type of arthritis, because of age or damage to the articular cartilage. Another form of joint disorder is TMJ syndrome where the joints in the jaw cause a clicking noise in the jaw and facial pain.

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FIGURE 1–24.  Synchondrosis. Reproduced with permission from Anatomage.

FIGURE 1–25.  Mandibular symphysis. Reproduced with permission from Anatomage.

FIGURE 1–26.  Synovial joint. Reproduced with permission from Anatomage.

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Organs An organ includes an amalgamation of tissues that are connected in a structural unit to serve a function. Organs are made up of a structural unit that is specific to that organ (e.g., the liver) and other tissues (e.g., blood vessels, nerves). When two or more organs are responsible for conducting a specific function in the body, an organ system is formed.

Systems For speech-language pathology, we identify three primary systems: respiratory, phonatory, and articulatory/resonance systems. The respiratory system is important for communication. As soon as a child is born, the respiratory system becomes functional when it comes into contact with air. The infant is able to breathe and use the power of the respiratory system to produce a voice with varying degrees of pitch and loudness. The phonatory system is responsible for voicing. It requires assistance from the respiratory system (breath stream) as well as the muscles of the larynx to produce sound. The articulatory/ resonance system changes the sounds that are emitted from the larynx and converts them to words that we identify as speech. In the process of producing speech, the vocal tract which includes the pharynx, oral cavities, and nasal cavities modifies the sounds and converts them to what we recognize as speech. There are several other systems in the body. When two or more organs combine, they form a system. These include the skeletal, nervous, circulatory, endocrine, respiratory, digestive, muscular, immune, lymphatic, excretory, integumentary, and reproductive systems. The immune system protects the body from disease. It is made up of proteins, tissues, cells, and organs that defend against disease. The lymphatic system is involved in the transfer of lymph between tissues and the bloodstream, the lymph, and the nodes and vessels that transport lymph. It includes the lymphatic vessel, lymph node, thymus, spleen, and bone marrow. The excretory system includes the kidney, ureters, urethra, and bladder. The integumentary system includes the skin, hair, and nails. The reproductive system includes the sex organs: penis, ovaries, fallopian tubes, uterus, vulva, vagina, testes, vas deferens, seminal vesicles, and prostate. The skeletal system (Figure 1–27) provides structural support and protection. It is made up of bones, tendons, ligaments, and cartilage. The skeletal system provides support to the body, keeps the internal organs in place, impacts movement, protects vital organs from being damaged, and helps with blood production. The endocrine system (Figure 1–28) communicates by using hormones produced by the thyroid, parathyroid, adrenal glands, and endocrine glands, which include the pituitary glands, pineal gland, and hypothalamus. The circulatory or cardiovascular system (Figure 1–29) pumps blood and lymph through the body. It moves oxygen and nutrients to cells and removes carbon dioxide from the body. It includes the heart, arteries, veins, and capillaries. The respiratory system (Figure 1–30) includes the organs used for breathing. These include the pharynx, nasal cavity, larynx, trachea, bronchi, lungs, and diaphragm. The digestive system (Figure 1–31) is involved in digestion and processing food. It includes the salivary glands, esophagus, stomach, liver, gallbladder, pancreas, intestines, colon, rectum, and anus. The muscular system (Figure 1–32) is involved with muscle movement. It includes the skeleton, tendons, joints, and ligaments. The nervous system (Figure 1–33) obtains, transfers, and processes information. It is made up of nerves, the brain, and the spinal cord. 27

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FIGURE 1–27.  Skeletal system. Reproduced with permission from Anatomage.

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FIGURE 1–28.  Endocrine system. Reproduced with permission from Anatomage.

FIGURE 1–29.  Circulatory system. Reproduced with permission from Anatomage.

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Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 1–30.  Respiratory system. Reproduced with permission from Anatomage.

FIGURE 1–31.  Digestive system. Reproduced with permission from Anatomage.

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FIGURE 1–32.  Muscular system. Reproduced with permission from Anatomage.

FIGURE 1–33.  Nervous system. Reproduced with permission from Anatomage.

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➤ Cranial Nerves The PNS is made up of the spinal nerves and cranial nerves. The cranial nerves send and receive messages from the head and neck, while the spinal nerves send and receive messages from the rest of the body. As their name implies, the cranial nerves are associated with the cranium (Figure 1–34), the bony part of the skull that encases and protects the brain: n

The cranial nerves connect muscles and structures of the head, face, and neck to the CNS.

n

There are 12 pairs of cranial nerves (meaning that there is one for the right side of the body and an analogous one for the left side of the body).

n

Based on the presence of certain speech, voice, or swallowing difficulties (i.e., what body parts are affected and how), a speech-language pathologist often can discern the presence of pathology in the PNS.

n

The cranial nerves are numbered by Roman numerals in the order that they synapse, or connect, to the CNS from superior to inferior. The olfactory nerve is numbered cranial nerve (CN) I, because from superior to inferior, it is the first cranial nerve to synapse with the CNS.

FIGURE 1–34.  Cranial nerve web. Reproduced with permission from Anatomage.

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In contrast, the hypoglossal nerve is CN XII because the other 11 cranial nerves attach to the portions of the brain and brainstem above it. n

The 12 pairs of cranial nerves are named with Roman numerals (I–XII) in the order they exit the brainstem and names that lend to their structure, function, or distinction.

n

The cranial nerves are either motor (efferent) nerves, sensory (afferent) nerves, or mixed sensory-motor (afferent-efferent) nerves: n

n

n

Cranial nerves that are motor in nature carry only efferent impulses from the CNS out to the muscles of the body. Cranial nerves that are sensory in nature transmit only afferent impulses from the body back to the CNS. The cranial nerves that function both as sensory and motor nerves relay both efferent and afferent information between the CNS and the body. (See Tables 1–3 and 1–4 for a complete listing of the cranial nerves and their functions.)

Olfactory Cranial nerve I (Figure 1–35) is the olfactory nerve. This nerve is afferent and helps with the sense of smell in the mucous membranes of the nasal cavity. There are about 20 nerves emanating from under the olfactory bulb located on the cribriform plate of the ethmoid bone. The nerve then moves anterior to a thin process of brain matter known as the olfactory tract. Technically, the olfactory nerve is not a real cranial nerve because it does not go through the thalamus before reaching the brain. The olfactory

TABLE 1–3.

Cranial Nerves Mnemonic

Cranial Nerve

Mnemonic (names/order)

Sensory/ Motor/Both

Mnemonic (sensory/motor)

I

Olfactory

On

Sensory

She

II

Optic

One

Sensory

Sings

III

Oculomotor

October

Motor

More

IV

Trochlear

Tuesday

Motor

Music

V

Trigeminal

The

Both

But

VI

Abducens

Autumn

Motor

My

VII

Facial

Fades

Both

Brother

VIII

Acoustic (vestibulocochlear)

And

Sensory

Says

IX

Glossopharyngeal

Grape

Both

Buying

X

Vagus

Vines

Both

Beats

XI

Accessory

Are

Motor

Makes

XII

Hypoglossal

Harvested

Motor

Magic

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Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

TABLE 1–4.

Cranial Nerves:  Origin, Type, Function

Roman Numeral

Cranial Nerve

Origin

Type

Function

I

Olfactory

Cerebral hemispheres

Sensory

Smell

II

Optic

Thalamus

Sensory

Vision

III

Oculomotor

Midbrain

Motor

Movement of the eyes

IV

Trochlear

Midbrain

Motor

Movement of the eyes

V

Trigeminal

Pons

Sensory Motor

Somatic sensation from face, lips, and jaw Movement of the mandible

VI

Abducens

Pons

Motor

Movement of the eyes

VII

Facial

Pons

Sensory Motor

Gustation (taste) from anterior two thirds of the tongue Movement of the lips and face

VIII

Vestibulocochlear

Pons, medulla

Sensory

Hearing and balance

IX

Glossopharyngeal

Medulla

Sensory

Gustation (taste) from posterior third of the tongue Moves superior portion of pharynx

Motor X

Vagus

Medulla

Sensory Motor

Sensation from larynx, pharynx, and abdominal viscera Movement of larynx, pharynx, and velum

XI

Accessory

Medulla, spinal cord

Motor

Movement of the muscles of the shoulder and neck (trapezius) Provides motor control to the muscles of the larynx, pharynx, and velum

XII

Hypoglossal

Medulla

Motor

Movement of the tongue

nerve is also a special visceral afferent nerve, and some consider it an extension of the brain itself. The olfactory nerve has a close relationship to taste, eating, and swallowing. Damage to the first cranial nerve can affect a person’s perception of taste.

Optic Cranial nerve II is the optic nerve. It is a paired sensory nerve and is responsible for relaying afferent information about vision from the retinas of the eyes toward the brain for processing. The optic nerve from the retina of each eye leaves the orbit (the eye socket) and proceeds medially and posteriorly to a point known as the optic chiasm. The optic chiasm (Figure 1–36) is the point at which the left and right

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FIGURE 1–35.  Olfactory nerve.

FIGURE 1–36.  Optic nerve.

optic nerves come together, and the medial fibers from each nerve decussate (cross over) to the opposite side to continue within the brain along the optic tract on the way to the occipital lobe where visual information is processed. The optic tract is the continuation of the optic nerve fibers through the brain: n

CN II is also considered an extension of the brain rather than a true cranial nerve. Each of the nerves are connected at the commissure on opposite sides.

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Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

n

This decussation of the medial sections of each optic nerve allows for an arrangement in which all visual information concerning the left side of each eye is sent to be processed in the right occipital lobe, and all visual information concerning the right side of each eye is sent to be processed in the left occipital lobe.

n

Each eye has a right and left visual field, and each side of the retina in each eye is responsible for receiving light from the opposite side of the environment. The right side of the retina in the right eye receives light from the left side of the environment, and the left side of the retina in the right eye receives light from the right side of the environment. Since the left occipital lobe receives all visual information about the right visual field in each eye, fibers from the medial retina of the right eye must cross to the left side of the brain at some point to carry that information from the right eye’s medial retina to the left occipital lobe — this occurs at the optic chiasm.

n

Damage to the optic nerve or the optic tract negatively affects vision. The visual fields that are lost depend on the location of the lesion along the optic tract or optic nerve.

n

This nerve is not associated with speech, language, or hearing.

Oculomotor Cranial nerve III is the oculomotor nerve that is an efferent cranial nerve that controls the movements of the eyeballs. This nerve also controls how the eye reacts to light and adducting/abducting the eyelids. The oculomotor nerve’s origin is thought to be the inner surface of the crus cerebri, anterior to the pons Varolii (gray). This nerve is made up of two parts — the general somatic efferent (GSE) and the general visceral efferent (GVE). The GSE ipsilaterally innervates the extrinsic ocular muscles such as the superior, medial, and inferior rectus muscles, the superior levator palpebrae, and the inferior oblique muscle. Intervention of these muscles leads to the eyes turning up and out, down and out, or inward. The GVE part of this nerve comes from the Edinger-Westphal nucleus, which is accessory oculomotor. The GVE controls the focus and the reflexes of the pupils. The oculomotor nerve is in close proximity to the circle of Willis making it easily affected by tumors, hemorrhages, and aneurysms.

Trochlear Cranial nerve IV is the trochlear nerve. It is an efferent nerve that moves the eyeball down. This nerve is typically categorized as a GSE nerve. It originates from the trochlear nucleus of the midbrain and ipsilaterally innervates the superior oblique muscle of the eye. This muscle turns the eyes down and out. A lesion to this cranial nerve could affect a person’s ability to turn the eyes down and out.

Trigeminal Cranial nerve V is the trigeminal (Figure 1–37). It is one of the largest cranial nerves and one of the most important cranial nerves for speech. It is a mixed motor and sensory nerve. The sensory aspect of this nerve controls the sense of touch on the face, while the motor aspect of this nerve innervates most of the muscles for mastication. The trigeminal emerges from the pons and splits into three primary branches: ophthalmic, maxillary, and mandibular: n The

ophthalmic branch is sensory in nature and transmits afferent information from the upper face, forehead, and scalp to the CNS. 36

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Introduction

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FIGURE 1–37.  Trigeminal nerve.

n The

maxillary branch is also a sensory nerve and is responsible for transmitting afferent information from the teeth, upper lip, buccal and nasal cavities, as well as the sides of the face to the CNS.

n The

mandibular branch has both sensory and motor functions. The afferent portion of this nerve carries sensory information from the lower teeth, lower gums, and bottom lip and somatic information from portions of the tongue. The efferent component of the mandibular branch of the trigeminal nerve innervates muscles of mastication.

This nerve is a crucial mixed nerve involved in the production of speech since it sends messages to the muscles of mastication and receives sensory messages from the face.

Abducens Cranial nerve VI is a motor nerve called the abducens. This nerve innervates the lateral rectus ocular muscle by entering the orbit at the superior orbital fissure. The lateral rectus ocular muscle abducts the eyeball. This nerve originates in the fourth ventricle in the abducens nucleus of the pons, then leaves the brainstem where the pons and medulla join. Damage here could cause diplopia (double vision) because the eyes would rotate medially (internal strabismus).

Facial Cranial nerve VII, the facial (Figure 1–38), is a mixed sensory-motor nerve. The facial nerve emerges from the inferior pons. The primary motor function of the facial nerve is to provide motor innervation to the muscles of the face. The primary sensory function of the facial nerve is to transmit afferent information about taste from the anterior two thirds of the tongue to the CNS: n

The facial nerve is important for speech production and communicates with other cranial nerves such as acoustic (VIII), trigeminal (V), vagus (V), glossopharyngeal (XI), and even some cervical nerves. 37

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 1–38.  Facial nerve.

n

The facial nerve has four branches. From superior to inferior, these are the temporal, zygomatic, buccal, and mandibular branches: n A distinctive feature of the facial nerve is that the temporal and zygomatic branches, which innervate the muscles of the upper face, receive plans of volitional motor movement for the upper face from the contralateral as well as the ipsilateral cerebral hemispheres. When one side of a paired nerve (e.g., the right or the left) receives motor plans from both the right and the left cerebral hemispheres, it is termed bilateral innervation. n In contrast, the inferior branches of the facial nerve, the buccal and the mandibular, which innervate the muscles of the lower face, are unilaterally innervated. Unilateral innervation of a nerve indicates that the nerve receives volitional motor plans from only the contralateral cerebral hemisphere. n There is a protective redundancy in bilateral innervation. With bilateral innervation, a lack of motor plans coming from one cerebral hemisphere does not completely incapacitate a body part if that part of the body can still receive motor plans from the opposite hemisphere. Figure 1–38 shows innervation of the superior portions of the facial nerve as well as the unilateral innervation of the inferior portions of the facial nerve.

Vestibulocochlear Cranial nerve VIII is the vestibulocochlear nerve, also known as the auditory nerve (Figure 1–39). It is a sensory nerve that carries sound from the cochlea to the brainstem and messages from the vestibular mechanisms in the inner ear that are involved in movement and balance. This nerve has both afferent and efferent components. The afferent side works with information concerning hearing and balance, and the efferent dampens parts of the output of the hair cells: n

This nerve has two sets of fibers, one comes from the vestibular ganglion (Scarpa ganglion) and is known as the vestibular branch. This nerve is related to a person’s orientation of three-dimensional space and equilibrium. The three peripheral branches go to the ampulla, 38

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Introduction

Introduction

1

FIGURE 1–39.  Vestibulocochlear nerve. Source: Figure 12.7 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 510), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

saccule, and utricle, located in the labyrinthine apparatus in the inner ear (Figure 1–39). The central fibers follow the path of the cochlear nerve and end in the vestibular nucleus. Some of the central fiber bundles go directly to the cerebellum, and others go to the numerous spinal and cranial nerve nuclei creating critical reflective pathways. The other set of fibers starts at the cochlear root and is known as the cochlear branch. The central fibers travel through the canal of the modiolus and move on into the internal auditory meatus. The peripheral fibers go to the hair cells in the cochlea. They end at the dorsal and ventral and dorsal cochlear nuclei. The efferent component of this nerve is a group of fibers known as the olivocochlear bundle. Though it is a small section of the 30,000 fibers that make up cranial nerve VIII, it affects how the hair cells communicate. It is thought that this section is managed by cortical activity activated by the signal detected from a noise.

Glossopharyngeal Cranial nerve IX is the glossopharyngeal (Figure 1–40). It has both sensory and motor functions. It innervates the tongue and the pharynx and carries some fibers that make up nerves in the autonomic nervous system. The primary sensory function of the glossopharyngeal is transmitting taste from the posterior one third of the tongue and also from a portion of the soft palate: n

The motor function of the glossopharyngeal nerve is to deliver efferent signals to the superior muscles of the pharynx, which are involved in swallowing, as well as to the parotid gland, which produces saliva. 39

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 1–40.  Glossopharyngeal nerve.

n

This nerve is made up of several branches (tympanic branch, carotid sinus nerve, pharyngeal branch, motor branch, and tonsillar and lingual branches). Some of these have a direct impact on the speech mechanism: n

n

Carotid sinus nerve: uses sensory fibers to innervate the internal carotid artery as blood pressure receptors.

n

Pharyngeal branch: innervates the mucous membrane of the pharynx.

n

Motor branch: innervates the stylopharyngeus muscle.

n

n

Tympanic branch: sends parasympathetic fibers to the parotid gland and the mucous membrane of the middle ear and eustachian tube.

Tonsillar and lingual branches: a complicated group that innervates the mucous membranes of the fauces (arch at the back of the mouth prior to the pharynx), posterior portion of the tongue, palatine tonsils, and the soft palate. A special function of this group’s sensory fibers is that it innervates the taste buds on the posterior one third of the tongue.

Cranial nerve IX works with fibers of the vagus nerve to help innervate the pharyngeal plexus, which travels to the upper pharyngeal constrictor muscles. Damage to this nerve would lead to a person losing the ability to taste on the posterior portion of the tongue.

Vagus Cranial nerve X, the vagus (Figure 1–41), is the largest cranial nerve. It is perhaps the most important cranial nerve for the speech-language pathologist. The vagus is a long and complex nerve with both sensory and motor functions. The nerve exits the medulla and travels inferiorly to innervate the muscles of the soft palate, pharynx, and larynx: n

Upon leaving the medulla, the first branch of the vagus innervating a structure important for speech is the pharyngeal plexus. This branch of the vagus innervates most of the muscles of 40

Introduction FIGURE 1–41.  Vagus nerve. Source: Figure 1.23 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 37), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

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Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

the inferior pharynx as well as most of the muscles of the velum. The muscles of the inferior pharynx are responsible for pharyngeal constriction, which is used during swallowing, while the muscles of the velum are important for sealing off the nasal cavity for production of nonnasal phonemes and for avoiding nasal regurgitation during swallowing. n

Continuing inferiorly, the second branch of the vagus that is important for speech is the superior laryngeal branch, or the superior laryngeal nerve (SLN). The SLN has an intrinsic and an extrinsic branch. The intrinsic branch of the SLN is sensory in nature and responsible for transmitting sensory information from the inside of the larynx to the CNS. The extrinsic portion of the SLN is responsible for innervating the cricothyroid muscle (the primary tensor of the vocal folds).

n

The vagus then courses and passes inferiorly into the thorax. The right vagus nerve passes under the right subclavian artery within the right side of the thorax. The left vagus passes under the arch of aorta of the heart within the left side of the thorax. Both of these branches then immediately change course and pass superiorly back, recurring, into the neck and to the larynx to innervate all the remaining intrinsic muscles of the larynx (those muscles responsible for adduction and abduction of the vocal folds). These branches of the vagus are known appropriately as the recurrent laryngeal nerve (RLN).

Accessory Cranial nerve XI, the accessory, is an efferent nerve and as such is only motor in function. The accessory nerve has a spinal component responsible for innervating muscles of the shoulders, such as the trapezius, but it also has a cranial component: n

The cranial component of the accessory nerve and the functional differences between it and the vagus nerve are poorly understood. The cranial component of the accessory nerve works alongside the vagus (as an accessory to the vagus) and often shares functions with the vagus. This part of the nerve begins at the nucleus ambiguous and comes out of the side of the medulla oblongata through four or five small rootlets. The fibers then move laterally to go through the jugular foramen. Branches then connect to the jugular ganglion of the vagus. The leftover fibers split up between the superior and pharyngeal branches of the vagus nerve. This part of CN XI innervates the levator veli palatini and the uvula. Some parts of the cranial section of the accessory nerve extend to the trunk of the vagus and are circulated to the RLN. n The spinal component of the accessory has fibers that originate from the anterior horn of the spinal cord as motor roots from cervical nerves one through five. The fibers then group together and make up a trunk that runs parallel to the spinal cord to the cranium. This part of the accessory nerve innervates the sternocleidomastoid and trapezius muscles.

Hypoglossal Cranial nerve XII is the hypoglossal (Figure 1–42). The hypoglossal nerve exits the brainstem at a more inferior location on the medulla than any other cranial nerve. The nerve then follows the path of the vagus and communicating branches to other cranial nerves and the first cervical nerve. The hypoglossal nerve is motor in nature. The primary role of the hypoglossal nerve is to innervate all the intrinsic muscles of the tongue and most of the extrinsic muscles of the tongue. The intrinsic muscles of the tongue are the muscles that comprise the actual body of the tongue and are responsible for the finer motor movements of the tongue involved in articulation. The extrinsic muscles of the tongue are those muscles responsible 42

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Introduction

1

FIGURE 1–42.  Hypoglossal nerve.

for gross movements of the tongue, such as the protrusion and retraction of the tongue. These gross motor movements of the tongue are more likely used during mastication and swallowing than during speech. The motor fibers of the hypoglossal also innervate some of the strap muscles of the neck (i.e., sternohyoid, sternothyroid, thyrohyoid, styloglossus).

➤ Chapter Summary Biology involves the study of living organisms. The human biological makeup includes cells, tissues, joints, organs, and systems. Anatomy and physiology are the study of the structure and function of organisms and their parts. Anatomy has two divisions. Macroscopic or gross anatomy uses unaided eyesight to study parts of an animal’s body. This includes superficial anatomy. Microscopic anatomy allows clinicians to use optical methods to observe structures and tissues inside a living person without dissection. This includes histology and cytology. Within the field of anatomy, there are several specializations including developmental anatomy, surface anatomy, comparative anatomy, general anatomy, descriptive anatomy, applied anatomy, radiological anatomy, and morbid anatomy. Physiology is a subdiscipline of biology and includes the study of the functions of living organisms and their parts. Physiology examines how organs, organ systems, organisms, cells, and biomolecules carry out the chemical processes that are inherent in a living organism. To study spatial relationships, it is necessary to have a point of reference when discussing structures of the body. The axial skeleton includes the bones of the trunk and head, and the appendicular skeleton includes the limbs as well as the skeletal structures in the limbs, the pelvic girdles, and the pectoral girdles. Anatomical terms are used for common locations on the body and anatomical surfaces. When using anatomical terms, the point of reference is the standard anatomical position where the body is at rest and standing erect with the feet together or slightly apart. The face is forward. The arms are at the side and rotated outward, with the palms facing

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Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

forward. The thumbs are pointed away from the body. There are three main planes of the body. The sagittal plane divides the body into right and left sides vertically. The frontal plane divides the body into front and back halves. The transverse plane divides the body into upper and lower parts. Cell structures are the basic structure all of living organisms and are the building blocks of life. Humans have trillions of cells that specialize in different functions, and each individual cell has several parts. A group of cells together form tissues. Tissues comprise many similar cells that are responsible for a particular function. The four basic types of tissues are epithelial, connective, muscular, and nervous. Epithelial tissue covers the outer surface, internal passages, and cavities of the body. There are several functions of epithelial tissues including sensory, absorptive, protective, glandular, and secretory. Connective tissue is found everywhere in the body and is composed of large quantities of extracellular substance, also known as the matrix. Connective tissue has three parts including fibers, ground substance, and cells. Fibers can be collagenous, elastic, or reticular. Ground substance is a fluid that slows down the spread of pathogens. There are many different types of cells including adipocytes, fibroblasts, leucocytes, macrophages, and mast cells. Connective tissue can be subdivided into connective tissue proper and specialized connective tissue. Muscular tissue can be skeletal, smooth, and cardiac. These tissues are formed during embryonic development and allow the muscles to contract. Nervous tissue is the primary component of the brain and spinal cord of the central nervous system (CNS) and the peripheral nerves of the PNS. Joints are where two bones are attached to allow body parts to move. They are classified based on how the bones connect to each other (structural classification) or by the amount of movement between the bones (functional classification). The three structural classifications of joints include fibrous, cartilaginous, and synovial. Fibrous joints are connected by dense regular connective tissue and have large amounts of collagen fibers. Cartilaginous joints are attached by cartilage. Synovial joints are bonded by dense irregular connective tissue but are not directly attached. The three functional classifications of joints include synarthrodial, amphiarthrodial, and diarthrodial. Synarthrodial joints allow little to no movement, amphiarthrodial joints allow some movement, and diarthrodial joints move freely. Organs are formed by grouping several tissues together. They are made up of a primary tissue and sporadic tissues. When two or more organs combine and are responsible for a particular function in the body, an organ system is formed. There are several systems in the body. These include the skeletal, nervous, circulatory, endocrine, respiratory, digestive, muscular, immune, lymphatic, excretory, integumentary, and reproductive systems. The skeletal system provides structural support and protection. The nervous system obtains, transfers, and processes information. The endocrine system communicates by using hormones produced by the thyroid, parathyroid, adrenal glands, and endocrine glands. The circulatory system pumps blood and lymph through the body. The respiratory system includes the organs that are primarily used for breathing. The digestive system is involved in digestion and processing food. The muscular system is involved with muscle movement. The immune system protects the body from disease. The lymphatic system is involved in the transfer of lymph between tissues and the bloodstream, the lymph, and the nodes and vessels that transport lymph. The excretory system includes the kidneys, ureters, urethra, and bladder. The integumentary system includes the skin, hair, and nails. The reproductive system includes the sex organs. The three systems that we primarily identify for speech-language pathology include the respiratory, phonatory, and articulatory/resonance systems.

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There are 12 pairs of cranial nerves that are motor (efferent), sensory (afferent), or mixed sensory-motor (afferent-efferent). The cranial nerves in order are as follows: olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, and hypoglossal. The olfactory nerve is responsible for smell. The optic nerve controls vision. The oculomotor, trochlear, and abducens nerves are all responsible for the movement of the eyes. The trigeminal nerve is responsible for somatic sensation from the face, lips, and jaw and also movement of the mandible. The facial nerve is responsible for gustation (taste) from the anterior two thirds of the tongue and movement of the lips and face. The vestibulocochlear or auditory nerve is responsible for controlling hearing and balance in the body. The glossopharyngeal nerve is responsible for gustation (taste) from the posterior one third of the tongue and movement of the superior portion of the pharynx. The vagus nerve controls sensation from the larynx, pharynx, and abdominal viscera. It also controls movement of the larynx, pharynx, and velum. The accessory nerve assists the vagus nerve with movement of the larynx, pharynx, and velum while also controlling movement of the shoulder and neck muscles. The hypoglossal nerve is responsible for controlling movement of the tongue.

➤ References Blumenfeld, H. (2010). Neuroanatomy through clinical cases (2nd ed.). Sinauer Associates. Hooke, R. (1665). Micrographia: Or some physiological descriptions of minute bodies made by magnifying glasses, with observations and inquiries thereupon. Royal Society. Kershaw, E. E., & Flier, J. S. (2004). Adipose tissue as an endocrine organ. Journal of Clinical Endocrinology and Metabolism, 89(6), 2548–2556. https:// doi.org/10.1210/jc.2004-0395 Klein, S. B., & Thorne, B. M. (2007). Biological psychology. Worth Publishers. Kolb, B., & Whishaw, I. Q. (2003). Fundamentals of human neuropsychology. Worth Publishers. Marieb, E., & Hoehn, K. (2007). Human anatomy and physiology (7th ed.). Benjamin Cummings. Polyzoidis, S., Koletsa, T., Panagiotidou, S., Ashkan, K., & Theoharides, T. C. (2015). Mast cells in meningiomas and brain inflammation. Journal of Neuroinflammation, 12(1), 170. https://doi.org/​ 10.1186%2Fs12974-015-0388-3 Purves, D., Augustine, G. J., Fitzpatrick, D., Hall, W.

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C., LaMantia, A. S., McNamara, J. O., & White, L. E. (2008). Neuroscience (4th ed.). Sinauer Associates. Sackmann, E. (1995). Biological membranes, architecture, and function. In A. J. Hoff, R. Lipowsky, & E. Sackmann (Eds.), Handbook of biological physics (Vol. 1A, pp. 1–64). Elsevier B.V. Schüz, A., & Braitenberg, V. (Eds.). (2002). The human cortical white matter: Quantitative aspects of cortico-cortical long-range connectivity. In Cortical areas: Unity and diversity, conceptual advances in brain research (pp. 377–386). Taylor and Francis. Standring, S. (2005). Gray’s anatomy: The anatomical basis of clinical practice (39th ed.). Elsevier Churchill Livingstone. Steele, D. G., & Bramblett, C. A. (1988). The anatomy and biology of the human skeleton. Texas A&M University Press. Tortora, G. J., & Derrickson, B. (2006). Principles of anatomy and physiology. John Wiley & Sons. White, T. D., Black, M. T., & Folkens, P. A. (2012). Human osteology (3rd ed.). Elsevier.

Introduction

1

2 Anatomy of Respiration

➤ Learning Objectives Upon completion of this chapter, students will be able to: n

Identify the individual bones that make up the bony framework of the thorax that supports respiration.

n

Identify the muscles that play a role in respiration.

n

Explain the molecular process of respiration at the alveolar level.

n

Explain and identify individual parts of the respiratory tract as well as the linkage between the thorax and the lungs.

n

Explain how muscles of respiration work to move the thorax for inspiration and expiration.

➤ Introduction to Respiration The process of exchanging gases between our bodies and the environment is respiration. We acquire oxygen from the air and expel carbon dioxide. Our brains alone use about 20% of the oxygen we take in. As humans, we require a steady supply of oxygen to survive, and even a brief intermission in the supply of oxygen is capable of causing brain damage and death. In addition to successfully taking in oxygen from the air, we must also successfully dispose of carbon dioxide by expelling these waste product molecules into the air that we then push out of our lungs. As our cells and tissues absorb and use oxygen, carbon dioxide is produced as a waste by-product of cellular metabolic processes. As a lack of oxygen means imminent death for us humans, so too does the inability to appropriately release carbon dioxide. Without the ability to discard of carbon dioxide, it will poison our bodies and cause unconsciousness, brain damage, and death. 47

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

A complete lack of oxygen for the purpose of respiration is known as anoxia, while an overabundance of carbon dioxide in the body is known as carbon dioxide poisoning, also known as hypercapnia. Both conditions are familiar to the speech-language pathologist, as those who survive these conditions have varying levels of brain damage as a result, and they often present for therapy to address acquired cognitive and language deficits. During respiration, our bodies pull air into the lungs for the purpose of bringing oxygen to the tissues of our lungs. The exchange of these gases occurs within tiny air sac–like structures at the end of the respiratory passes within the lungs. These air sacs responsible for gas exchange are the alveoli. Inspiration is the process of pulling air into the lungs. As molecules of oxygen are moving from the oxygen-rich air in the lungs into the oxygen-poor blood in the circulatory system, carbon dioxide is moving from the carbon dioxide–rich blood in the circulatory system through the thin walls of the alveoli into the carbon dioxide–poor air within the lungs. Conversely, expiration is the process of pushing carbon dioxide–rich air from inside the lungs back into the environment. Once this exchange of gases has occurred at the alveoli, the freshly oxygenated blood travels to the heart to be pumped out and distributed among the cells and tissues of the body to sustain life. Due to the importance of respiration to survival, this process is usually completed under autonomic control of the nervous system, meaning that the body breathes automatically with no volitional or cognitive effort to ensure the body is constantly and appropriately inspiring oxygen and expiring carbon dioxide. However, the process of respiration can be placed under volitional control, at least for a short period of time. You can temporarily alter the rate of respiration at will; but if your respiration is too slow or too fast, you will eventually pass out, and your body will automatically return your rate of respiration to normal to maintain normal physiological processes to keep you alive. Nonetheless, an advantage of our partial volitional control of the respiratory process is that it allows us to hijack the process of expiration for the production of voice and speech. During expiration, we bring together the vocal folds to produce voice. We also vary other points of constriction within the pharynx, oral cavity, and nasal cavity during expiration for the production of all vowels and consonants of speech.

Anoxia and Hypoxia Any condition that deprives the body of appropriate levels of oxygen intake is likely to damage the body. A complete lack of oxygen to the body or portion of the body is termed anoxia. A less extreme level of oxygen deprivation is hypoxia. More often than not, when anoxia and hypoxia are discussed in a medical setting, it is in the context of major organs such as the brain being deprived of oxygen. Cerebral anoxia or cerebral hypoxia specifically refers to a lack of oxygen to the brain and as mentioned earlier is a common scenario to the speech-language pathologist. In a case of cerebral anoxia, which is often caused by failure of the heart to deliver blood to the brain, tissues of the brain begin to experience death and permanent brain damage within 4 to 6 minutes. The first areas of the brain to perish from lack of oxygen in a case of cerebral anoxia are usually those areas of the brain that require the most oxygen to survive. Typically, these are cells of the hippocampi that are largely responsible for creation of memory as well as the output cells (Purkinje cells) of the cerebellum that help create smoothly integrated, smoothly articulated, and error-free body movement. Hence, many individuals who survive conditions of cerebral anoxia or cerebral hypoxia will have significant memory deficits as well as uncoordinated and errorful body movements from cerebellar damage that negatively impacts speech, creating what is known as ataxic dysarthria.

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Anatomy of Respiration

Examples of this include bringing the lips together to build up a pressurized release of expiration for the production of the /p/ or elevating the tip of the tongue to hover just behind the teeth, not quite touching the roof of the mouth, narrowing the expiratory airstream into the hiss of the /s/ phoneme. To truly understand how we use respiration for the exchange of oxygen and carbon dioxide in our environment and for the production of voice and speech, we must first know all the structures of the body directly associated with these functions. Before one can understand how the soft tissues of the body function for respiration, one must first know the skeletal scaffolding that provides the framework on which our soft tissues are held and housed.

The tissues that comprise the thorax are divided into the bony thorax and the visceral thorax.

The Bony Thorax The bony thorax includes the vertebral column, rib cage, and pectoral girdle. The bony thorax is the rigid bone of the thorax that provides structure to the thorax and support to soft tissues of the thorax. The portion of the bony thorax that provides support and scaffolding for the rib cage and pectoral girdle is the vertebral column. The rib cage and pectoral girdle are suspended from the vertebral column with the visceral thorax within, protected and housed by the rib cage. The vertebral column consists of 32 or 33 individual bones (Figure 2–1) known as vertebrae resting on top of each other and forming the framework for the superior portion of the skeleton. These vertebrae have a layer of hyaline cartilage on their articular surfaces for smooth gliding. Between the inferior articular surface of one vertebra and the superior articular surface of the vertebra below it, there are discs of tough fibrocartilage known as

FIGURE 2–1. Divisions of the vertebral column. Reproduced with permission from Anatomage.

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Anatomy of Respiration

➤ The Skeletal Framework for Respiration

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

intervertebral discs. These intervertebral discs provide cushioning and allow flexibility between the vertebrae. The intervertebral discs allow for vertebrae to be cushioned from the weight of the upper body they support, while the hyaline cartilage allows the vertebrae to smoothly and slightly rotate on top of each other. There are five types of vertebrae that make up the human vertebral column. From superior to inferior (Figure 2–1), these are the seven cervical vertebrae, twelve thoracic vertebrae, five lumbar vertebrae, four to five fused sacral vertebrae, and three to five fused coccygeal vertebrae. The cervical, thoracic, and lumbar vertebrae are individual bones that articulate and connect with each other via the cartilaginous discs and ligaments between them. In contrast, the sacral and coccygeal vertebrae are fused into the two respective structures of the sacrum and the coccyx. These fused portions of the vertebral column have ossified intervertebral discs present. Vertebrae are identified by the first letter of their particular section of the vertebral column followed by the number of the vertebra in question counted from superior to inferior within that particular section of vertebrae. For example, the first cervical vertebra is C1. The second cervical vertebra from the top of the cervical vertebrae is C2. The third thoracic from the first thoracic vertebra is T3. Each of these divisions of vertebrae has a distinct anatomy that reflects its function in the body. Although each type of vertebrae has significant anatomical differences, there are general features and structures shared by the cervical, thoracic, and lumbar vertebrae. The anterior cylindrical mass of a vertebra is the corpus or body (Figure 2–2), and this is the weight-bearing portion of the vertebra. On either side of the corpus, two projections known as the pedicles (Figure 2–2) attach to the posterior section of the vertebra. These pedicles fuse with posterior plates known as laminae (Figure 2–2). From the laminae, the transverse processes are bony projections that project laterally (Figure 2–2). At midline, the laminae come together and project posteriorly to form the spinous process (Figure 2–2). The spinous process is easily found on your own back by running your hand down the middle of your back. The bumps felt there are the spinous processes of your vertebrae being felt through the various layers of muscle and other soft tissue. The pedicles and laminae fuse to form a foramen (a hole or space) against the corpus. This is the vertebral foramen (Figure 2–2), and it protects and houses the spinal cord. The cervical, thoracic, and lumbar vertebrae have lateral openings that are formed between the interlocking vertebrae. These are the intervertebral foramina (Figure 2–3). The intervertebral foramina are openings between the articulating vertebrae between which the roots of the spinal nerves exit the vertebral column.

FIGURE 2–2.  Cervical vertebrae. Reproduced with permission from Anatomage.

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Divisions of the Vertebral Column Although the cervical, thoracic, and lumbar vertebrae (Figure 2–1) have many similarities, each section of the vertebral column has individual functions and anatomical characteristics particular to that section of the vertebral column. The differing functions and anatomy of the different types of vertebrae are detailed next, following the order of these sections of the vertebral column from superior to inferior: n

Cervical vertebrae: The cervical vertebrae, being the most superior, are the vertebrae of the neck and are stacked between the thoracic vertebrae and the skull: n n

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There are seven cervical vertebrae (Figure 2–1). This section of the vertebral column bears the least amount of weight of any other section of the vertebral column since they bear only the weight of the head and neck. Because of this, the cervical vertebrae are noticeably smaller and more delicately structured than those vertebrae in other inferior sections of the vertebral column. Distinguishing characteristics of the cervical vertebrae include the widening vertebral foramen and the presence of a transverse foramen within each transverse process (Figure 2–4). The transverse foramina form a vertical passage through the transverse processes on each side of each cervical vertebra through which the vertebral arteries pass on their superior course toward the base of the brain (Figure 2–5). The superior-most two cervical vertebrae (C1, C2) are specialized in function and anatomy and are distinct even among the cervical vertebrae: n

n

The first cervical vertebra (C1) is known as the atlas (Figure 2–6). Just as Atlas is the mythical Greek figure who holds up the earth, the function of C1 is to provide a resting point for the skull on the top of the vertebral column, thereby holding the base of the skull. The skull articulates with the atlas via the superior articular facets of the atlas. The second cervical vertebra (C2) is known as the axis (Figure 2–7). This name reflects the second cervical vertebra’s function of being the structure on which the atlas articulates and rotates. The axis has an anterior projection known as the odontoid or the dens. The odontoid articulates superiorly with the atlas and provides an interlocking relationship between the atlas and the axis. This interlocking of the atlas and axis (Figure 2–8) protects the spinal cord by preventing the disassociation of these two vertebrae, which would seriously damage the enclosed spinal cord. 51

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FIGURE 2–3. Intervertebral foramina. Reproduced with permission from Anatomage.

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FIGURE 2–4.  A. Superior view displaying anatomy of seventh cervical vertebra (C7). B. Lateral view displaying anatomy of seventh cervical vertebra (C7). Reproduced with permission from Anatomage.

FIGURE 2–5.  Cervical arteries passing through the cervical vertebrae. Reproduced with permission from Anatomage.

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FIGURE 2–6.  A. Superior view of atlas (C1). B. Lateral view of atlas (C1). Reproduced with permission from Anatomage.

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FIGURE 2–7.  A. Superior view of axis (C2). B. Lateral view of axis (C2). Reproduced with permission from Anatomage.

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Thoracic vertebrae:  Beneath the cervical vertebrae are the thoracic vertebrae. The thoracic vertebrae are larger in mass than cervical vertebrae (Figure 2–9). A primary role of the thoracic vertebrae is to provide posterior points of attachment for the rib cage: n n

There are 12 thoracic vertebrae (Figure 2–1). The thoracic vertebrae are essential to the process of respiration by providing posterior attachment points for the rib cage, which is itself essential to respiration. It is through muscular movement of the rib cage by which air is pulled into the lungs during inspiration to then be passively squeezed out of the lungs during expiration. 53

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FIGURE 2–8.  Articulation of atlas and axis vertebrae. Reproduced with permission from Anatomage.

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FIGURE 2–9.  A. Superior view of a thoracic vertebra. B. Lateral view of a thoracic vertebra. Reproduced with permission from Anatomage.

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Distinctive features of the thoracic vertebrae are the superior, inferior, and transverse costal facets (Figure 2–9) that are the points of attachments between the ribs and the thoracic vertebrae (see Figure 2–16, p. 60). The thoracic vertebrae also have significantly more massive spinous and transverse processes that provide a greater and stronger surface area for larger and stronger muscles.

Lumbar vertebrae: The lumbar vertebrae are located beneath the thoracic vertebrae and are the vertebrae of our lower backs bearing most of the weight of the upper body. As a result of their role as weight-bearing structures, the lumbar vertebrae are very large and significantly 54

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more massive than the thoracic and cervical vertebrae, with thicker and stronger transverse and spinous processes (Figure 2–10). These thicker and stronger transverse and spinous processes provide attachment points for the muscles of the lower back as well as for the diaphragm, the primary muscle of inspiration: n n

The lumbar can be readily identified by the lack of transverse foramina possessed by the cervical vertebrae and by a lack of costal facets present on the thoracic vertebrae.

Sacral vertebrae:  Inferior to the lumbar vertebrae of the lower back and superior to the coccygeal vertebrae are the sacral vertebrae. The sacral vertebrae consist of four to five fused vertebrae that form a single triangular bone known as the sacrum (Figure 2–11). The sacrum has a concave anterior surface and convex posterior surface that projects inferiorly and has a slight anterior curve: n

The sacrum articulates laterally with the ilium of the pelvis and as such provides the central weight-bearing portion of the pelvic girdle.

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FIGURE 2–10.  Anatomy of lumbar vertebrae. Reproduced with permission from Anatomage.

FIGURE 2–11.  Sacrum. Reproduced with permission from Anatomage.

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There are five lumbar vertebrae (Figure 2–1).

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The fusing of the sacrum begins around puberty and can continue until age 30 years. Sacral foramina (Figure 2–11) provide passages for sacral nerves entering and exiting the spinal cord.

Coccygeal vertebrae:  The inferior-most portion of the vertebral column projecting inferiorly from the sacrum are the coccygeal vertebrae. The coccygeal vertebrae are three to five vertebrae fused into a single mass known as the coccyx (Figure 2–11): n n

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The coccyx articulates superiorly with the sacrum through an intervertebral disc. Whereas the more superior sections of the coccyx have some distinguishable but diminished vertebral features such as less prominent transverse processes, they entirely lack pedicles and laminae. The most inferior coccygeal vertebra is merely a portion of bone with no distinguishable vertebral features.

Sternum Also known as the breastbone, the sternum is the prominent anterior and midline structure of the thorax that provides a point of attachment for the clavicles (collarbones) and for many ribs (Figure 2–12). The sternum is composed of three primary divisions. From superior to inferior, these are the manubrium sterni, the corpus (or body), and the xyphoid (or ensiform) process (Figure 2–12): n

Manubrium sterni n n

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The manubrium sterni is the superior-most portion of the sternum. The manubrium sterni provides sites of attachment between the clavicles (collarbones) and the sternum as well as the first two ribs and the sternum (Figure 2–13). These points of attachment on the manubrium sterni where it connects with the clavicles are the clavicular facets, while the points of attachment where the manubrium sterni connects with ribs are known as costal facets.

FIGURE 2–12.  Sternum. Reproduced with permission from Anatomage.

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FIGURE 2–13.  Rib cage. Reproduced with permission from Anatomage.

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The clavicular facets are superior to the first costal facet. The top of the manubrium sterni is bounded laterally by the clavicles to form the sternal notch. The sternal notch can be easily felt by placing your hand on either clavicle and following it to midline at the base of your neck. The first ribs attach to the manubrium at the first costal facets. The point at which the manubrium sterni and the corpus fuse is the manubriosternal angle. The second rib attaches to the second costal facet, which occurs laterally on the sternum at the manubriosternal angle. In this way, the manubrium sterni provides attachment points for the clavicle, the first ribs, and a portion of the second ribs.

n Corpus n

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The corpus is the body of the sternum and provides direct attachments for ribs three through seven. The corpus provides indirect attachment for ribs eight, nine, and ten (the false or vertebrochondral ribs).

n Xyphoid n

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The xyphoid is a delicate and pointed bony projection extending inferiorly from the corpus. The xyphoid was referred to by early anatomists as resembling the point of a sword. Whereas the manubrium sterni and the corpus provide points of articulation between the sternum and the clavicles and ribs, the xyphoid has no such features. The xyphoid can be easily found after locating the sternal notch by moving the hand inferiorly along the sternum until the termination point of the sternum (the inferior end of it) is located. 57

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Rib Cage The rib cage creates the general structure of the thoracic cavity (Figure 2–13) and provides housing and protection for the lungs. The rib cage is also the framework by which expansion and contraction of the lungs for respiration are possible. The rib cage is composed of 12 pairs of ribs (Figure 2–13). All the ribs originate posteriorly at the thoracic vertebrae (see Figure 2–15, p. 60). Ribs 1 through 10 attach anteriorly directly or indirectly to the sternum. From the posterior, the ribs course laterally and curve down and toward the anterior before bending back toward midline to attach in the anterior at the sternum. This gives the rib cage the characteristic barrel-like shape. Ribs are numbered from superior to inferior, similar to the vertebrae (Figure 2–13). For example, the first and most superior pair of ribs (right and left) is referred to as R1, while the last and most inferior pair of ribs (right and left) is referred to as R12. The rib cage is composed of three types of ribs: vertebrosternal ribs, vertebrochondral, and vertebral (Figure 2–13): n

Ribs 1 through 7 (R1 through R7) are the vertebrosternal ribs. The vertebrosternal ribs are also known as the true ribs. This is because they articulate directly with the thoracic vertebrae posteriorly and the sternum in the anterior. The first rib articulates with the sternum through a synchondrosis, which is an unmoving joint where the connecting tissue is hyaline cartilage. The remaining true ribs articulate with the sternum via synovial joints and with the thoracic vertebrae via arthrodial joints. The vertebrosternal ribs have an anterior section of costal cartilage that serves as the attachment point between these ribs and the sternum.

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Ribs 8, 9, and 10 (R8, R9, R10) are the vertebrochondral ribs. The vertebrochondral ribs are also known as the false ribs. These ribs attach directly to the thoracic vertebrae posteriorly. Anteriorly, R8, R9, and R10 reach superiorly to attach the costal cartilage of rib seven. The vertebrochondral ribs thereby attach to the sternum indirectly through the costal cartilage of rib seven.

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Ribs 11 and 12 (R11, R12) are the vertebral ribs. The vertebral ribs are also known as the floating ribs because despite their posterior attachments at the thoracic vertebrae, they are about half the length of the other ribs and have no anterior point of attachment. Rather than connecting anteriorly with the sternum, the vertebral ribs are left with no anterior attachment, and their anterior section is left floating in soft tissue.

Anatomy of a Rib.  All the ribs have discernable and common features due to their structure and attachments. From most posterior to anterior, these features are as follows (Figure 2–14): n The

head of each rib is the terminal posterior section of the rib that articulates via the corpus of the thoracic vertebrae through superior and inferior costal facets on the corpus of the thoracic vertebrae.

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Moving posteriorly away from the head of the rib, the neck is that portion of the rib that exists between the ribs’ terminal attachments at the corpus of the thoracic vertebrae and the secondary attachment of the rib on the transverse process of the thoracic vertebrae.

n The

tubercle of the ribs is that small concave indention or cup-like feature on the posterior surface of the rib that articulates with the transverse process of the thoracic vertebrae. This point of articulation between the transverse processes of the thoracic vertebrae and the tubercles of the ribs occurs at the transverse costal facets of the thoracic vertebrae.

n The

shaft of the ribs is most of the bulk of the ribs. It is mostly a thin, flat section of bone convex on the external surface and concave on the internal surface. Posteriorly, it begins at the tubercle and by virtue of its body and shape provides most of the structure of the rib cage.

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FIGURE 2–14.  Anatomy of a rib. Reproduced with permission from Anatomage.

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On the inferior section of the ribs, there exists a groove that runs lengthwise along the shaft. This is the costal groove. The costal groove houses associated intercostal nerves and blood vessels.

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Moving laterally away from midline, shortly after the tubercle, the shaft suddenly bends to course inferiorly and toward the anterior. The angle of the ribs is this point where the shaft changes its direction to course forward.

Attachments Between Ribs and the Sternum and Vertebrae.  In the anterior, most ribs attach to

the sternum (Figure 2–13). The details of those attachments were discussed earlier. Although there are 12 thoracic vertebrae and 12 ribs, the ribs often do not articulate with the thoracic vertebrae in a one-on-one manner, although some do (Figures 2–15 and 2–16): n

The points of articulation between the ribs and corpus of the thoracic vertebrae are the costovertebral joints (Figure 2–16). The term costo refers to the ribs while vertebral refers to the vertebrae.

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The points of articulation between ribs at the tubercle of the rib and the transverse processes of the thoracic vertebrae are the costotransverse joints (Figure 2–16).

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Ribs 1, 10, 11, and 12 each articulate posteriorly to only a single corresponding thoracic vertebra. These ribs articulate with their associated thoracic vertebrae at the transverse and superior costal facets. Following these ribs posteriorly from the sternum, they curve around the body and when reaching the vertebral column, they first articulate with the corresponding single thoracic vertebra at the transverse costal facet of the thoracic vertebra. From there the neck of rib curves inward, and the head articulates for a second time with the same thoracic vertebrae at the superior costal facet.

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Ribs 2 through 9 each articulate posteriorly to two thoracic vertebrae. Each of these ribs articulates at the transverse costal facet and superior costal facet of one thoracic vertebra as do ribs 1, 10, 11, and 12. However on ribs 2 through 9, the head of the rib extends superiorly to articulate also with the inferior costal facet of the thoracic vertebra above (Figure 2–15).

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FIGURE 2–15.  Transverse and spinous process. Reproduced with permission from Anatomage.

FIGURE 2–16. Superior view of articulation of rib and a thoracic vertebra. Reproduced with permission from Anatomage.

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So, whereas ribs 1, 10, 11, and 12 have two points of articulation with a single corresponding thoracic vertebra, ribs 2 through 9 have three points of articulation across two thoracic vertebrae.

The articulation of the ribs at their sternal attachments is through synovial joints, with the exception of the first rib, which has a synchondrodial joint at its sternal attachment. The primary articulation of the ribs at their attachments at the corpus of the thoracic vertebrae is through gliding arthrodial joints. Movement of the Rib Cage During Respiration.  The anterior cartilaginous portions of the ribs, the cartilaginous sternum, as well as the arthrodial posterior articulation of the ribs with the thoracic vertebrae give a degree of elasticity to the rib cage. This elasticity allows the expansion and retraction of the thoracic cavity along two planes, anteroposterior and transverse, for the purposes of respiration. This elasticity allows the rib cage to rock forward (anteroposterior dimension) while also expanding laterally (transverse dimension) (Figure 2–17). Inferior expansion (vertical dimension) of the thorax is also accomplished during respiration, but this expansion is primarily accomplished through the contraction and lowering of the large dome-shaped muscle, the diaphragm, which is the floor of the thoracic cavity.

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For the purposes of respiration and specifically inspiration, the thoracic cavity must expand to increase the volume of the lungs, which pulls air into the lungs: n

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The muscles of inspiration will pull the ribs forward and up to expand the rib cage in an anteroposterior dimension (Figure 2–17). Other muscles of inspiration will contract to slightly rotate the curved ribs lengthwise, thereby causing the expansion of the thorax laterally in the transverse dimension.

The pelvic girdle is the bony portions of the lower regions of the abdomen, also often referred to as the bony pelvis (Figure 2–18). The pelvic girdle provides the skeletal framework that connects the lower extremities (the legs) to the vertebral column. Because of this arrangement, the pelvic girdle bears the weight of the body above it that is then transferred and supported by the legs during activities such as walking.

FIGURE 2–17.  Movement of rib cage. Reproduced with permission from Anatomage.

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FIGURE 2–18.  A. Anterior view of pelvic girdle. B. Lateral view of pelvic girdle. Reproduced with permission from Anatomage.

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The Pelvic Girdle

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The pelvic girdle provides points of origin for most of the abdominal muscles. The abdominal muscles provide appropriate postural support that is important to the process of respiration and also support speech through their role in forced expiration. The pelvic girdle consists of three primary sections; laterally these are the ilium, inferiorly the ischium, and anteriorly the pubic bones (Figure 2–18). The ilium, ischium, and pubic bones together constitute the three parts of what is often collectively referred to as the bone of the hip, or os coxae. The ilium fuses posteriorly at the sacrum while the bilateral pubic bones fuse medially and anteriorly to create the ring-like structure of the pelvic girdle. n The

ilium is the large, fan-shaped superior, lateral, portion of the pelvic girdle — the hip bones: The ilium provides points of attachment for most of the muscles of the abdomen. n The most superior edge of the ilium is known as the iliac crest. When you place your hands on your hip bones, you are touching the iliac crests of the ilium. n The points of articulation between the ilium on either side of the sacrum are known as the sacroiliac joints. n

n The

ischium is located inferior to the ilium and is a posterior structure of the pelvic girdle: n The posterior section of the ischium is a large section of bone that bears body weight in a sitting position and is known as the ischial tuberosity. n The superior portion of the ischium forms the inferior and lateral portions of the acetabulum, which is the large socket into which the head of the femur inserts and articulates.

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The sacrum sits at midline between the ilium and is the triangular section of fused sacral vertebrae described previously.

n The

pubic bone or the pubis is the inferior and anterior portion of the pelvic girdle. The ramus of the pubic bone extends medially from the acetabulum to meet at midline: n The anterior and medial section of the acetabulum is formed by the pubic bone. n The pubic bones meet at a midline joint between them known as the pubic symphysis. n The pubic bone is closely associated with reproductive organs. n During childbirth, the baby passes through the ring of the pelvic girdle that is formed anteriorly by the pubic bone. In females, during pregnancy this joint becomes more flexible, increasing the odds of the baby’s skull (which is also flexible due to suture joints of the baby’s skull remaining cartilaginous) passing successfully through the pelvis.

Pectoral Girdle The pectoral girdle consists of the clavicle and scapula and is the point of origin of some muscles of respiration. These bones are arranged to provide an attachment between the arms, and the thorax (Figure 2–19). The pectoral girdle provides the same function to the arms as the pelvic girdle does to the legs. However, the anatomy between the pectoral girdle and pelvic girdle differs greatly due to the differences in range of motion of the arms compared to the legs as well as the legs’ weight-bearing ability. The only skeletal point of connection for the pectoral girdle is the sternoclavicular joint, the point at which the clavicle articulates with the sternum (Figure 2–20): n

Also known as the collarbone, the clavicle is positioned horizontally in the body and is the anterior portion of the pectoral girdle. The clavicle has a slight s shape curvature and connects to the manubrium sterni medially and projects laterally to the scapula.

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FIGURE 2–19.  Pectoral girdle. Reproduced with permission from Anatomage.

FIGURE 2–20.  Sternoclavicular joints. Reproduced with permission from Anatomage.

FIGURE 2–21.  Posterior view of scapula. Reproduced with permission from Anatomage.

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scapula is the thin, flat, and triangular bone that is also known as the shoulder blade and is the posterior portion of the pectoral girdle (Figure 2–21): n Located on the posterior of the body, the scapula is associated posteriorly and superficially with the posterior portions of the first eight pairs of ribs. 63

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The only point of attachment between the scapula and the rest of the skeleton is the clavicle. The only point of attachment the clavicle has to the rest of the skeleton is at the manubrium sterni. n Whereas the scapula attaches anteriorly to the clavicle, the scapula has no posterior connection to another bone. Despite the lack of a posterior attachment to the rest of the skeleton, the clavicle is supported posteriorly through many muscles. n The glenoid fossa is the facet formed by the scapula into which the head of the humerus, the large bone of the upper arm, attaches. n The scapula has three processes; the spinous process, acromion process, and coracoid process (Figure 2–21): n The spinous process of the scapula is on the posterior surface of the scapula and projects laterally to articulate with the clavicle. n The acromion process is the most superior and lateral-most point of the scapula that projects above the glenoid fossa. The acromion process is the point of articulation between the scapula and the clavicle. n The coracoid process is the point of attachment between the arm and pectoral muscles of the chest. The coracoid process is a bony projection of the scapula. The coracoid process projects between the acromion and the glenoid fossa. It is superior to the glenoid fossa and inferior to the acromion process. n

➤ The Visceral Thorax The visceral thorax includes the major organs and soft tissues of the thorax, which perform all manner of life-sustaining functions. Included in this are the heart, lungs, respiratory passages, and associated connective tissue and muscles. Not all of the structures of the visceral thorax are associated with respiration. However, this chapter focuses on those tissues and organs of the visceral thorax responsible for respiration.

Respiratory Passages Those tissues and structures that are directly responsible for exchange of gases and through which air moves during the process of respiration are the respiratory passages. The respiratory passages are divided into two sections: the upper respiratory tract and the lower respiratory tract. The upper respiratory tract (Figure 2–22) includes, from superior to inferior, the nasal and oral cavities, the pharynx, and the larynx. The lower respiratory tract (Figure 2–23) includes the respiratory passages below the larynx; from superior to inferior, these include the trachea and all branches of the bronchial tree down to the alveoli.

Nasal Cavity The nasal cavity (Figure 2–22) is the mucosal membrane–lined air-filled space behind the nares, or nostrils, responsible for warming and filtering inspired air. The anterior boundary of the nasal cavity is the nares. The posterior boundary of the nasal cavity is the nasal choanae, which is the point at which the nasal cavity opens into the pharynx posteriorly. The lateral walls of the nasal cavity are established by the bones of the face and skull. Both the oral and nasal cavities open posteriorly into the pharynx.

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FIGURE 2–22.  Upper respiratory tract.

FIGURE 2–23.  Lower respiratory tract. Reproduced with permission from Anatomage.

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Oral Cavity The oral cavity (Figure 2–22) is the mouth. The oral cavity is part of the digestive tract and is where food enters the body; it is also an important part of the respiratory tract and is vital for articulation. The anterior boundary of the oral cavity is the lips. The oral cavity is bounded superiorly by the hard and soft palates and inferiorly by the floor of the mandible on which the tongue rests.

Pharynx The pharynx (Figure 2–22) is a vertical muscular tube that provides the link for air to move from the nasal and oral cavities inferiorly into the larynx. The pharynx also is the link for transmission of food from the oral cavity inferiorly to the esophagus. The walls of the pharynx are composed of muscles that are responsible for contracting and directing solids and liquids that are being swallowed safely over the opening of the airway into the esophagus.

Larynx The larynx is anterior and inferior to the pharynx, superior to the trachea, and is an adaptation of the upper tracheal cartilaginous rings that form a structure that houses the vocal folds (Figure 2–24). The larynx and vocal folds provide a protective valve mechanism in the respiratory passage that allows for the valuable ability to close off the respiratory passage to keep foreign material, such as food, liquid, and saliva, from falling into the lungs and creating infection. This valve mechanism also creates the ability to have a protective cough or throat clear to expel any foreign or obstructive material that does fall into the airway from the pharynx. This valve ability of the larynx also allows for the production of phonation; furthermore, it allows for thoracic fixation: n

Thoracic fixation, also known as a Valsalva maneuver, is a squeezing together of the vocal folds, sealing off the lower respiratory tract and system during forcible expiration to increase intrathoracic pressure in order to use this pressure in the thorax to push down on the abdomen for important biological functions (defecation, urination, childbirth) and also to rigidify the torso for physical actions such as heavy lifting.

Thoracic Fixation Thoracic fixation/Valsalva maneuver is easily modeled. Imagine you are going to push against or lift a heavy or immovable object. Right before you would initiate the actual pushing or lifting, you will notice that you will take a sharp intake of breath followed by quick adduction of the vocal folds and simultaneous contraction of thoracic muscles probably experienced as a general tightening of the muscles of the chest. This is the Valsalva maneuver. This action rigidifies the torso making it easier to perform lifting and pushing.

Trachea The trachea is inferior to the larynx and is a single open tube with up to 20 horseshoe-shaped rings of hyaline cartilage, with the incomplete section of the rings to the posterior (Figures 2–24 and 2–25). The 66

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FIGURE 2–24.  Larynx and trachea. Reproduced with permission from Anatomage.

FIGURE 2–25.  Bronchial tree. Reproduced with permission from Anatomage.

trachea is the major passage for air between the larynx and the lungs. An adult trachea ranges from 1.5 to 2.5 centimeters in diameter and from 10 to 12 centimeters in length, and its structure is as follows: n

A fibrous membrane and smooth muscle exist between the rings of the trachea and bind them together.

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of the trachea to accommodate greater inspiration and expiration of air during active respiration when the body is requiring more oxygen. n

The trachea is superiorly bound by the cricoid cartilage of the larynx and inferiorly bound at the point of bifurcation of the trachea into the left and right primary bronchi that serve as passageways through which air is delivered to the lungs (Figure 2–25). This point of bifurcation of the trachea into the right and left primary bronchi is known as the carina (Figure 2–25).

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The inside of the trachea has an epithelial lining that is ciliated and contains goblet cells. Goblet cells produce mucus that functions to protect the lungs by catching foreign particles in inspired air as this air is being pulled by the body into the lungs. The cilia in the epithelial tissue continuously beat upward to move this mucus superiorly toward the vocal folds to be expelled during a cough or clearing of the throat.

Bronchial Tree Once the trachea branches into the primary left and right bronchi, these primary bronchi further subdivide into smaller and smaller branches in what is referred to as the bronchial tree (Figure 2–25): n The

primary bronchi serve as airways to the lungs, while the secondary bronchi subdivide from the primary bronchi at each lung to serve the individual lobes of the lungs.

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The secondary bronchi further subdivide into tertiary bronchi, which serve the individual segments of each lobe of each lung. The tertiary bronchi further subdivide into 20 to 25 divisions (Amador & Varacallo, 2020). These progressively smaller airways conclude with the terminal respiratory bronchioles.

n The

terminal respiratory bronchioles supply air to the tiny sacs of air that contain the alveoli, which are the location of gas exchange (i.e., respiration).

Angles of Primary Bronchi Off the Carina Leading to Right Lower Lobe Pneumonia When the trachea divides into the left and right primary bronchi, it is important to notice that the left primary bronchus bifurcates from the trachea at a sharper angle than the right primary bronchus (Figure 2–25). An outcome to this difference is that any foreign matter that falls into the airway (i.e., is aspirated) is more likely to fall into the right primary bronchus than the left. This is because to fall into the left primary bronchus requires a greater change of direction of the aspirated matter than the right primary bronchus (recall inertia: moving objects tend to keep moving in the same direction). This creates a situation in which foreign matter such as aspirated food and drink is more likely to end up resting in the lower lobe of the right lung and causing pneumonia there. Therefore, right lower lobe pneumonia is often closely associated with the possibility of aspiration and often requires a referral to the speech-language pathologist to confirm or rule out the possibility of aspiration causing the pneumonia.

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Lungs The lungs are the primary organs of respiration and house the major passages and structures that allow the human body to absorb oxygen and release carbon dioxide (Figure 2–26): There are two lungs, left and right, enclosed within the thorax and protected by the rib cage. n The base of each lung is concave, as it rests on the dome-shaped diaphragm. n The apexes of each lung reach high into the thorax to the base of the neck at 1 to 2 cm above the clavicle within the thorax. n The tissue of the lungs is spongy and elastic, allowing it to be stretched for inspiration and return to its original position during expiration. n The lungs are not identical and vary from each other in size, mass, volume, and height. n The right lung is larger than the left lung. It is shorter but wider than the left lung. This is due to the presence of the liver in the right side of the abdominal cavity, which extends high into the superior abdomen, thereby reducing the vertical space available to the right lung within the right side of the thoracic cavity. n The left lung is smaller than the right because it shares the left side of the thorax with the mediastinum, the thoracic cavity that contains the heart and associated cardiovascular structures.

Lobes of the Lungs As mentioned previously, the right and left lungs have various anatomical differences related to their size and structure. These differences extend to the subdivisions of each lung known as the lobes of the lungs (Figure 2–27): n

The lobes of the lungs are large, distinct divisions of the lungs created by large fissures in the tissue of the lungs and are served by the secondary bronchi.

FIGURE 2–26.  Cadaver lungs. Reproduced with permission from Anatomage.

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FIGURE 2–27.  Lobes of the lungs. Reproduced with permission from Anatomage.

n

The right lung has three distinct lobes. These are known as the superior, middle, and inferior lobes (Figure 2–27).

n

The left lung has only two lobes, inferior and superior (Figure 2–27).

Pleural Membranes of the Lungs The lungs are held fast within the thorax via a double layer of tissue known as the pleural membranes. The pleural membranes, also known as the pleurae or pleural linings, are delicate, thin, and vascular layers of tissue composed mostly of a layer of simple epithelial cells known as mesothelium. Mesothelium is the type of epithelial cell that composes the lining of many cavities of the body. Each lung is encased in its own independent and sealed pleural membrane. The pleural membranes allow for the smooth and gliding expansion of the lungs with the lowering of the diaphragm and expansion of the thorax: n

The pleural membrane that wraps and encases the lungs is known as the visceral pleura (Figure 2–28).

n

The pleural membrane that lines the inside walls of the thorax, including costal surfaces and the inferior border of the thorax at the diaphragm as well as the mediastinum, is the parietal pleura (Figure 2–28).

n

The visceral pleura is directly attached to the lungs, and the parietal pleura is directly attached to the interior of the thorax and superior portion of the diaphragm.

n

The cavity between these two layers of pleurae is known as the intrapleural space (Figure 2–28). It is important to note that in a healthy individual, the pleural membranes are in continuous contact with each other, and there is no actual space between the pleural membranes. These two layers of pleurae articulate directly with each other and remain in constant contact with each other through an airtight vacuum and a thin layer of intrapleural fluid that exists between the two membranes.

n

A lubricating secretion known as surfactant is present between the pleural membranes. This lubrication, along with the vacuum between the layers, is what connects the lungs to the thorax and to the diaphragm.

n

This vacuum that exists in the intrapleural space causes the lungs to follow and move with the rib cage when the thorax expands or retracts. In short, there is a suction or vacuum between 70

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FIGURE 2–28. Pleurae.

the visceral pleura and the parietal pleura that causes the lungs to follow the thorax and expand along with it when the thorax is expanded by muscular action. n

The vacuum state creating the connection between the visceral and parietal pleurae is known as the pleural linkage. If the seal creating the pleural linkage between the lungs and interior of the thorax is compromised (for instance, by a knife or gunshot wound to the thorax) and external air is allowed into the intrapleural space, the vacuum between the visceral and parietal pleurae will neutralize. In this situation, the lung will have no connection to the thorax and will not follow the expansion of the thorax, and inspiration will be difficult and painful. This is the condition known as a pneumothorax or collapsed lung (Figure 2–29).

Pleurisy In a healthy individual, when pleurae rub against one another during respiration, there is a smooth gliding action between the pleurae, and there is no friction between them. However, if the pleural membranes get infected, they may become irritated, swollen, or damaged. This can increase friction between the pleural membranes during respiration. This friction can further irritate the pleurae, causing a very sharp pain in the chest during respiration as well as shortness of breath. Pleurisy is any damage or inflammation of the pleural linings that creates these symptoms. Usual etiologies of pleurisy are bacterial or viral infections, pneumonia, pulmonary embolisms, auto­immune disorders, as well as traumatic etiologies such as fractures of ribs or chest wounds.

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FIGURE 2–29. Pneumothorax.

Respiratory Tissue and Gas Exchange The first and the majority of the divisions of the bronchial tree are responsible for transporting air to the deeper divisions and are not actively involved in the gas exchange process. The last few divisions of the bronchial tree lead to areas known as respiratory zones that contain alveoli and are where exchange of gases actually occurs. The final division of the bronchial tree within the respiratory zones includes the terminal respiratory bronchioles mentioned previously: n

Once the bronchial tree has progressed in its divisions to the terminal respiratory bronchioles, which are the last and smallest of the bronchioles, these small tubes open into the alveolar ducts.

n The

alveolar ducts are the passageways that transport air directly into the alveolar sac (Figure 2–30).

n The

alveolar sacs are chambers off which the individual alveoli are formed (Figure 2–30).

n

The walls of the alveolar sacs are shaped into many tiny compartmental depressions known as the alveoli. There are about 700 million alveoli in a pair of human lungs.

n

The alveoli (singular: alveolus) are where gas exchange during respiration occurs, so the more alveoli a person has, the greater is the surface area of tissue the person has dedicated to respiration, and the easier the work of respiration is. Conversely, the fewer the alveoli a person has, perhaps decreased by disease, the more difficult the work of respiration is. 72

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FIGURE 2–30. Alveoli.

n

The alveoli are very small, and the walls of the alveoli consist of a single layer of epithelial cells resting on a base membrane of matrix.

Each alveolus is enwrapped in capillaries (Figure 2–30). This intimate relationship between the alveoli and blood supply via the capillaries allows gas exchange to occur: n

The thin walls of the alveoli allow for free exchange of molecules of oxygen and carbon dioxide between the air in the alveoli, known as the alveolar air, and the blood in the capillaries encasing the alveoli. This exchange, oxygen in and carbon dioxide out, is the actual process of respiration: n

n

n

n

Deoxygenated blood is sent to the lungs from the right ventricle of the heart through the pulmonary artery to the lungs. The system of pulmonary arteries divides and subdivides into ever-smaller branches, eventually reaching the size of very fine and thin-walled capillaries that envelop each alveolus (Figure 2–30). Molecules of carbon dioxide are released from the deoxygenated blood through the thin walls of the capillary and alveolus into the alveolar air. Simultaneously, oxygen is transferred from the alveolar air through the walls of the alveolus and the capillary into the bloodstream. Following the capillaries away from the alveoli, they come back together to form ever larger branches of the pulmonary veins (Figure 2–30) that eventually deliver freshly oxygenated blood back to the heart for general circulation within the body. 73

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Chronic Obstructive Pulmonary Disease Chronic obstructive pulmonary disease (COPD) (Figure 2–31) is a number of degenerative diseases of the lungs, of which emphysema is one. Emphysema is most often caused by long-term smoking of tobacco or environmental exposure to lung irritants, which seriously damages the alveoli. The damage created by chronic smoking or environmental exposure to environmental irritants causes a breakdown of the walls of the alveoli over time. This reduces a person’s overall surface area of alveolar tissue below that which is required for effortless respiration, making respiration effortful and difficult. COPD causes great discomfort and eventual death as the alveolar tissue necessary for respiration continues to degrade, further reducing the body’s ability to acquire oxygen.

FIGURE 2–31.  Lung with signs of chronic obstructive pulmonary disease. Source: CDC Public Health Images Library/Dr. Edwin P. Ewing, Jr.

➤ Muscles of Respiration Having discussed the bony thorax and visceral thorax that support respiration, it is important to address the associated musculature that is responsible for the movement of this framework. Movement of the thorax and lungs is essential for normal respiration. It is the muscles associated with the bony thorax that expand the thorax and thereby increase volume of the lungs for inspiration and allow for the retraction of the lungs and reduction in lung volume for expiration. This increase in volume of the lungs pulls air into the body for inspiration, while a decrease in the volume of the lungs pushes air out of the lungs back into the environment.

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There are two general patterns of respiration to be considered before discussing the muscles that create respiration: quiet respiration and forced respiration. Quiet respiration occurs naturally as a person is breathing softly with the body exerting little physical effort. During quiet respiration, inspiration is accomplished using primarily the contraction of the diaphragm. The diaphragm contracts and lowers, which inferiorly increases the volume of the lungs in the vertical dimension. This inspiration created by the diaphragm acting alone is known as quiet inspiration. Quiet inspiration is the level of inspiration that is necessary to maintain life with minimal energy exerted. However, expiration during quiet respiration is passive expiration, meaning that no muscle activation is involved. Rather, the passive forces of gravity on the thorax and the passive force of the recoil of elastic tissues of the lungs and thorax return the thorax to its original position after being displaced momentarily by the diaphragm. Retraction of the thorax allows the lungs to recoil to their position at rest, thereby reducing lung volume and pushing air out of the lungs back into the environment. Retraction of the thorax continues until expiration is complete and the body is in position for the next inspiration. One quiet inspiration and one passive expiration is one cycle of quiet respiration. Average adults will complete around 12 cycles of quiet breathing per minute. During periods of physical exertion, quiet respiration is incapable of supplying the necessary levels of oxygen intake to the body and completing carbon dioxide removal from the body. During what is known as forced respiration, additional muscular activity is used to increase the amount of air inspired and expired and to increase the rate of respiration. During the inspiration phase of forced respiration, the volume of air in the inspiration phase is increased above that of the inspiratory volume of quiet respiration. This forced inspiration employs the diaphragm as well as the accessory muscles of inspiration to further increase the volume of air inspired to bring more oxygen into the body more quickly. This increase in air being inspired is accomplished by the accessory muscles of inspiration working to pull the rib cage superiorly and anteriorly, while also working to expand the transverse (lateral) dimension of the rib cage. This is in addition to the simultaneous action of the diaphragm increasing the vertical dimension of the thorax by pulling the lungs inferiorly. The actions of the accessory muscles of inspiration paired with the diaphragm cause an increase in the volume of air being inspired into the lungs above that observed in quiet inspiration. During the expiration phase, forced respiration utilizes activation of muscles of expiration to more quickly complete expiration. This forced expiration uses the muscles of expiration to expire more air and to do it more quickly.

Categorization of Muscles of Respiration The muscles involved in respiration are categorized according to their level of involvement with either inspiration or expiration: n

As the diaphragm plays such a large role in inspiration, it is categorized as the primary muscle of inspiration.

n

Other muscles involved in forced inspiration are known as the accessory muscles of inspiration. The accessory muscles of inspiration are discussed later.

n

The muscles involved in forced expiration are categorized as the muscles of expiration. Any muscle that may contribute to pulling the rib cage inferiorly or any muscle that works to displace the abdominal viscera to push the diaphragm superiorly back into its resting position can function to assist in expiration and be considered a muscle of expiration.

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Patterns of Muscular Use in Respiration

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n

Those muscles of expiration associated with the abdomen that displace the diaphragm superiorly are categorized as the primary muscles of expiration while all muscles that function to pull the rib cage inferiorly are categorized as accessory muscles of expiration.

Primary Muscle of Inspiration The diaphragm is the primary muscle of inspiration and is a large dome-shaped muscle that creates the anatomical division between the thoracic cavity containing the lungs and heart and the abdominal cavity containing the stomach, intestines, liver, spleen, and kidneys. It is one of the largest muscles of the human body and aside from the heart is the most important for sustaining life due to its important role in respiration (Figures 2–32, 2–33, and 2–34). When at rest, the diaphragm sits in a superior position of rest that is more anterior than posterior: n

The diaphragm has three primary areas of attachment to bone: the sternum, the rib cage, and the vertebral column (Figure 2–32). The anterior-most attachment of the diaphragm is at the posterior of the xyphoid process. Lateral attachments of the diaphragm are the inferior ribs. Posterior attachments are at the lower thoracic vertebrae T12 and at the first two upper lumber vertebrae. These lumbar attachments occur through two tendons known as the right crus and the left crus, which course down to attach to L1 and L2.

n

Muscle fibers of the diaphragm course from these origins at the xyphoid, inferior rib cage, and lumbar vertebrae, to insert into a large maple leaf–shaped piece of connective tissue known as the central tendon (Figure 2–32).

n

The central tendon is a strong and flat type of tendon known as an aponeurosis.

n

The diaphragm creates the boundary between the thorax and abdomen. However, there must still be interactions between these two sections of the body, such as sharing and distribution of

FIGURE 2–32. Diaphragm.

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B

FIGURE 2–33.  A. Inferior view of diaphragm. B. Anterior view of diaphragm in context with lungs. Reproduced with permission from Anatomage.

FIGURE 2–34.  Anteroposterior view of diaphragm on x-ray. Source: CDC Public Health Images Library/Dr. Thomas Hooten.

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blood flow and inferior travel of food and drink from the oral cavity through the esophagus to the stomach, which is located in the abdomen. This happens through three primary openings in the diaphragm: aortic hiatus, foramen vena cava, and esophageal hiatus (Figures 2–32 and 2–33): n

n

n

The aortic hiatus (Figure 2–32) is the opening through which the abdominal aorta passes on its way from the heart into the abdomen to supply oxygenated blood to the lower half of the body. The foramen vena cava (Figure 2–32) is the opening in the diaphragm through which the inferior vena cava passes in its course from the lower half of the body to deliver deoxygenated blood back to the heart. The foramen vena cava is located at the level of the eighth or ninth thoracic vertebrae. The esophageal hiatus (Figure 2–32) is the opening in the diaphragm through which the esophagus passes on its course down to the stomach and is located posterior to the central tendon. The esophageal hiatus exists at the level of the tenth thoracic vertebrae and is formed by the early fibers of the right crus as they originate from the central tendon left of center and cross to the right side of the body to form the tendinous right crus.

Innervation (nervous supply to) of the diaphragm is accomplished by the phrenic nerve: n

The phrenic nerve is a paired spinal nerve. Paired indicates that although it is referred to as a single structure (e.g., the phrenic nerve), there is a left phrenic nerve for the left side of the diaphragm and a right phrenic nerve for the right side of the diaphragm.

n

The phrenic nerve is responsible for transmitting motor (efferent) information from the spinal cord to the diaphragm and for transmitting sensory (afferent) information back to the spinal cord for processing in the central nervous system.

n

The phrenic nerve is bilaterally innervated. Bilateral innervation means that the left and right phrenic nerves each have connections to both sides of the central nervous system. Functionally, this means that if one side of the brain is damaged, the intact uninjured side of the brain will be able to get motor supply to both the right phrenic and left phrenic, thereby more likely ensuring survival.

Accessory Muscles of Inspiration Any muscle that can elevate the rib cage can be said to play a part in forced inspiration. These muscles that may have other primary functions but may also be engaged for forced inspiration are referred to as the accessory muscles of inspiration. Many different muscles can arguably be used for elevation of the rib cage and, therefore, forced inspiration. The accessory muscles of inspiration are categorized as follows according to their associated location on the body: rib cage, chest (anterior thorax), neck, and back (posterior thorax).

Accessory Muscles of Inspiration of the Rib Cage The accessory muscles of inspiration of the rib cage both originate and insert on the rib cage (Figure 2–35). These muscles are paired and include the external intercostals and the chondral (cartilaginous) portion of the internal intercostals. External Intercostals.  Aside from the diaphragm, the external intercostals are the most important

muscles for inspiration. The external intercostals are known as intercostals because they exist between (inter) the ribs (costals). Furthermore, they are the external intercostals because they are external (super­ficial) 78

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FIGURE 2–35.  Internal and external intercostals.

to a similar and antagonistic muscle group that assists in expiration known as the internal intercostals, which are covered in the discussion of the muscles of expiration. The fibers of the external intercostals course diagonally and at right angles to the internal intercostals and bind the rib cage together, providing a significant layer of protection to vital thoracic organs such as the heart and lungs: n

The external intercostals begin to occur posteriorly near the spinal column at the tubercle of each rib. They cease to occur anteriorly on the lateral boundaries of the ribs near the anterior chondral portions of the ribs. The external intercostals cease well before nearing the sternum.

n

There are 12 pairs of ribs that create 11 spaces between the ribs. There are, therefore, 11 pairs of external intercostals in these 11 spaces.

n

Toward the anterior of the body, near the chondral portion of the rib cage, the external intercostals transition from muscle fiber to aponeurosis: n

n

n

n

Origin n Inferior boundary of each rib Insertion n Muscle fibers course diagonally downward and anteriorly to insert into the rib below. Innervation n Provided by the spinal nerves, specifically the thoracic intercostal nerves that are associated with the first through the sixth thoracic vertebrae Function n Contraction of the external intercostals expands the thoracic cavity by elevating the ribs, flaring the rib cage laterally outward in the transverse dimension and elevating the rib cage forward and anteriorly. 79

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This elevation of the rib cage occurs due to the elasticity of the anterior chondral portion of the rib cage, which bends outward and expands forward and laterally upon contraction of the external intercostals. Also allowing this to occur is the gliding articulation of the posterior articulation of the ribs with the vertebrae that allows the rib cage to rotate up and outward when pulled by the external intercostals while the sternum stays parallel to the vertebral column. n The elevation and expansion of the rib cage by the external intercostals are important for respiration when the body needs more oxygen than is being provided by quiet respiration (diaphragm alone). To respond to this need, the external intercostals can be employed to greatly increase the volume of air being inspired. n In addition, the external intercostals are important for speech production because they allow for the greater volume of air inspired that is necessary to speak in longer utterances and with a louder voice. n

Chondral Portion of Internal Intercostals.  The internal intercostals are primarily muscles of expira-

tion and are discussed later (Figure 2–35). However, the chondral portion of the internal intercostals, which exists between the chondral portions of the rib cage (those cartilaginous portions of the ribs associated medially and anteriorly with the sternum), function differently by virtue of their position, and play a role in forced inspiration: n

The chondral portion of the internal intercostals is the anterior-most section of the internal intercostals and is associated closely with the sternum and the anterior cartilaginous portion of the rib cage.

n

The chondral portion of the internal intercostals activates segmentally separate from the rest of the internal intercostals during forced inspiration to elevate the rib cage, assisting the external intercostals in forced inspiration.

Accessory Muscles of Inspiration of the Chest (Anterior Thorax) The accessory muscles of inspiration of the chest are muscles that have medial attachments to the rib cage and distal attachments to the shoulder. These muscles are paired and include the pectoralis major, pectoralis minor, serratus anterior, and subclavius (Figure 2–36). Pectoralis Major. The pectoralis major, commonly known as one’s pecs, are strong and large fanshaped muscles of the chest, which are located anteriorly and superficially on the thorax (Figure 2–37): n

Most of the muscle mass of the chest is composed of the pectoralis major.

n

The pectoralis major attaches at three points on the body: the clavicle, the humerus, and the sternum.

n

The pectoralis major has two major divisions: the superior section of muscle known as the clavicular portion and the inferior section of muscle known as the sternal-costal portion: n Origin n Clavicle and crest of the greater tubercle of the humerus n Insertion n Anterior surface of the sternum n Innervation n The medial and lateral pectoral nerves that arise from the brachial plexus 80

n

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FIGURE 2–36.  Anterior view of accessory muscles of inspiration of the chest. Reproduced with permission from Anatomage.

FIGURE 2–37.  Pectoralis major. Reproduced with permission from Anatomage.

n

Function n Rotate or adduct the shoulder and arm medially n When the clavicle is held in a fixed position, contraction of the fibers of the pectoralis major will elevate the sternum, thereby expanding the rib cage in the transverse dimension for forced inspiration.

Pectoralis Minor. The pectoralis minor is a small muscle that occurs on the anterior superior thorax

beneath the pectoralis major (Figure 2–38): n

The fibers of this muscle course laterally and superiorly from its origins on the ribs: n

n

Origin n Anterior of ribs 3, 4, and 5, close to but not contacting the chondral portion of the rib cage Insertion n Scapula at the coracoid process 81

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Innervation n Medial and lateral pectoral nerves that arise from the brachial plexus n Function n Stabilize the scapula n When the scapula and shoulder are held in a fixed and immobilized position, the pectoralis minor will assist in elevating the rib cage for forced inspiration. n

Serratus Anterior. The serratus anterior is a fan-shaped muscle positioned laterally on the thorax

(Figure 2–39): n

The serratus anterior has individual extensions of muscle associated with each rib. As these extensions originate along the first nine ribs, a sawtooth-like appearance is created. This sawtooth-like appearance gives the muscle its name of serratus. Since there is an analogous muscle on the posterior of the body (the serratus posterior), this is the anterior serratus: n Origin n External boundary of the first nine ribs and courses superiorly to insertion

FIGURE 2–38.  Pectoralis minor. Reproduced with permission from Anatomage.

FIGURE 2–39.  Serratus anterior. Reproduced with permission from Anatomage.

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Insertion n Medial portion of the scapula n Innervation n Long thoracic nerve that is a branch of the brachial plexus with nerve fibers arising from spinal nerves C5 to C7 n Function n Stabilize the scapula or to move the scapula anteriorly n If the serratus anterior muscles are contracted with a scapula held in a fixated position, it can assist in elevating the associated ribs (1–9) for forced inspiration. n

rib (Figure 2–40) that is deep to the pectoralis major:

Origin n Near the sternum at the junction between the chondral and osseous portions of the first rib n Insertion n Courses laterally and slightly superiorly from origin to insert at the inferior clavicle, specifically at the subclavian groove n Near the acromion process of the scapula n Innervation n By the subclavian nerve, which arises as a branch of the brachial plexus n Portions of the brachial plexus that become the subclavian nerve originate from spinal nerves C5 and C6. n Functions n Stabilize the clavicle and move the shoulder anteriorly and inferiorly n However, due to its location and points of connection, if the shoulder is held in a fixed position, contraction of the subclavius can function to assist in elevating the first rib to assist in inspiration. n

FIGURE 2–40.  Subclavius. Reproduced with permission from Anatomage.

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Subclavius. The subclavius is a short muscle of the shoulder located between the clavicle and the first

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Accessory Muscles of Inspiration of the Neck Any muscle that has an attachment at the neck and courses inferiorly to attach to the rib cage may function to pull the rib cage superiorly, thereby assisting forced inspiration. The muscles of the neck reviewed here that can contribute to forced inspiration are the scalenes (anterior, middle, and posterior) and sternocleidomastoid. These accessory muscles of inspiration associated with the neck are paired muscles. Scalenes. The scalenes are a group of three pairs of muscles deep to the sternocleidomastoid muscle

(Figure 2–41). The scalenes course from the cervical vertebrae of the neck down to the first two ribs. The name of these muscles originates with the Greek word skalenos, which means “uneven.” This word is applied to these muscles based on their staggered or uneven appearance: n

A primary function of the scalenes is to stabilize and rotate the head. However, due to their attachments, they are also capable of elevating the rib cage. Innervation is via the fourth, fifth, and sixth cervical spinal nerves. Due to differences in points of attachment and orientation, the anterior, middle, and posterior scalenes have slightly different functions when contracted in isolation from one another: n The anterior scalenes have an almost vertical orientation as they angle out slightly to either side as they course from the cervical vertebrae inferiorly to the first rib (Figure 2–42). n Due to this vertical orientation and attachment to the first rib, bilateral contraction of the anterior scalene can function to elevate the first rib on each side of the rib cage for inspiration: n Origin n On the transverse processes of vertebrae C3 to C6 n Insertion n Superior surface of the first rib n Innervation n Anterior scalenes are innervated by cervical spinal nerves C5 and C6.

FIGURE 2–41. Scalenes (anterior, medial, and posterior). Reproduced with permission from Anatomage.

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Function n Elevate the first rib for inspiration

n The n

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middle scalenes are the largest of the three pairs of scalenes (Figure 2–43).

These muscles are oriented at a more horizontal and less vertical angle as compared to the anterior scalenes as they course inferiorly: n Origin n Transverse processes of vertebrae C3 to C7 n Insertion n Superior surface of the first rib deep to the anterior scalenes n Innervation n Middle scalenes are innervated by cervical spinal nerves C3 through C8.

FIGURE 2–42. Anterior scalenes. Reproduced with permission from Anatomage.

FIGURE 2–43. Middle scalenes. Reproduced with permission from Anatomage.

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n

n

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FIGURE 2–44.  Posterior scalenes. Reproduced with permission from Anatomage.

n

Function n Unilateral contraction of a middle scalene will rock the head toward the side of the contraction. Bilateral contraction will assist in elevating the first ribs for inspiration.

n The n

posterior scalenes are the smallest of the scalenes (Figure 2–44).

The posterior scalenes have an even more horizontal orientation than the middle scalenes and course more laterally to reach out over the first rib to insert on the second rib below: n

n

n

n

Origin n Transverse processes of vertebrae C5 to C7 Insertion n Superior surface of the second rib Innervation n Posterior scalenes are innervated by cervical spinal nerves C6 through C8. Function n Bilateral contraction will assist in elevating the second rib for inspiration. Unilateral contraction will pull the neck to tilt it toward the side of muscle contraction.

Sternocleidomastoid. The sternocleidomastoid is so named because of its three attachments. These three attachments are at the sternum (sterno), at the clavicle (cleido), and at the mastoid (mastoid) process of the temporal bone of the skull (Figure 2–45). This paired muscle is located anteriorly and laterally on the neck and is prominently displayed when the head is rotated toward one side of the body: n

It consists of two portions: the sterno-mastoid portion and the cleido-mastoid portion.

n

The sterno-mastoid portion of the muscle projects almost vertically from the manubrium of the sternum. The cleido-mastoid portion of the muscle is shorter and originates laterally to the sternal head of the muscle and projects vertically and medially to merge with the muscle fibers of the sterno-mastoid portion of the muscle.

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FIGURE 2–45.  Sternocleidomastoid. Reproduced with permission from Anatomage.

n

Once both portions of the originating muscle fibers are merged, the sternocleidomastoid projects vertically to insert at the mastoid process of the temporal bone. If you place your hand behind the inferior portion of your ear, you will feel a bump. That is the mastoid process: n

n

n

n

Origin n From a head on the manubrium process of the sternum (sterno-mastoid portion) and a head on the clavicle (cleido-mastoid portion) Insertion n Mastoid process of the temporal bone Innervation n The spinal portion of the 11th cranial nerve, cranial nerve XII, the accessory nerve Function n Rotate the head left or right through unilateral contraction if the sternum and clavicle are held fixed n If the head is held fixed and the sternocleidomastoids are contracted bilaterally, they will function to pull upward on the sternum and clavicle, thereby assisting in elevating the rib cage for forced inspiration.

Accessory Muscles of Inspiration of the Back (Posterior Thorax) Any muscle that has attachments at the vertebral column and courses inferiorly to attach to the rib cage may function to elevate the rib cage upon contraction to assist in forced inspiration. These muscles of the posterior thorax that can contribute to forced inspiration are the serratus posterior superior, levator costarum (brevis and longis), levator scapulae, latissimus dorsi, and trapezius (Figure 2–46). These accessory muscles of inspiration of the posterior thorax are paired muscles. Serratus Posterior Superior. The serratus posterior superior (Figure 2–47) is a thin and superficially situated muscle of the upper back. The name of the muscle, serratus posterior superior, holds much useful

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FIGURE 2–46.  Accessory muscles of inspiration of the back. Reproduced with permission from Anatomage.

FIGURE 2–47.  Serratus posterior superior. Reproduced with permission from Anatomage.

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information. The term serratus is applied due to the sawtooth-like appearance of the insertion points of the individual extensions of the muscle. The term posterior is applied because this muscle is on the back, and the term superior because it is on the superior portion of the back:

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Origin n Spinal processes of the seventh cervical vertebrae through the third thoracic vertebrae Insertion n Fibers of this muscle course laterally and inferiorly at an angle to insert into the posterior surface of the second through the fifth ribs. Innervation n Accomplished via the T1 through T4 spinal nerves Function n Elevates the ribs it inserts into to assist in forced inspiration

Levator Costarum (Brevis and Longis).  As the name implies, the levator costarum muscles function

to elevate (levate) the ribs (costarum). There are 12 pairs of levator costarum. The levator costarum are located posteriorly and medially on the ribs on either side of the vertebral column. These muscles course inferiorly and obliquely from their more medial origins on the rib cage. These muscles are divided into two primary portions according to their length, the shorter group known as levator costarum brevis (i.e., brief, short) and the longer group known as levator costarum longis (i.e., long) (Figure 2–48):

FIGURE 2–48.  Levator costarum brevis and longis.

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Origin n The origins of the levator costarum brevis are on the transverse processes of the seventh cervical vertebrae through the 11th thoracic vertebrae. n The origins of the levator costarum longis are on the transverse processes of the seventh through 11th thoracic vertebrae. Insertion n Levator costarum brevis course inferiorly from their origins to insert into the tubercle of the rib right below. n Levators costarum longis are longer than the brevis portion because as they course inferiorly, they skip the rib directly beneath their origin and insert into the following rib, thereby following a course twice as long as the brevis group. Innervation n The levator costarum are innervated by the spinal nerves C8 through T11. Function n Levator costarum brevis and longis function to elevate the ribs during forced inspiration.

Levator Scapulae. The levator scapulae are located at a posterior lateral location on the neck and are

so named due to its function of elevating the scapula (Figure 2–49): n

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Origin n From the transverse processes of the first through fourth cervical vertebrae (C1 through C4) Insertion n This muscle courses inferiorly from its origin on the cervical vertebrae to insert on the posterior superior surface of the scapula. Innervation n The fourth and fifth cervical nerves

FIGURE 2–49.  Levator scapulae. Reproduced with permission from Anatomage.

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FIGURE 2–50.  Latissimus dorsi. Reproduced with permission from Anatomage.

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Function n Stabilizes and elevates the scapula n By fixing the scapula, this muscle can also assist in pulling and rotating the head ipsilaterally. With bilateral contraction and fixation of the head and neck this muscle may assist in elevating the rib cage for forced inspiration.

Latissimus Dorsi. The latissimus dorsi is a large, superficial muscle of the lower back that is primarily

important for movement of the arm (Figure 2–50): n

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Origin n This muscle originates on the lower thoracic vertebrae, lumbar vertebrae, sacrum, and ribs 10, 11, and 12 and the iliac crest by way of a large aponeurosis. It courses laterally and superiorly to insert into the upper humerus. Insertion n Courses laterally and superiorly to insert into the upper humerus Innervation n Latissimus dorsi is innervated by the sixth, seventh, and eighth cervical nerves. Function n Assists in depressing the arm n If contracted while the humerus is fixed, it will work to elevate the ribs during forced inspiration.

Trapezius. The trapezius is a large, flat, and the most superficial muscle of the back. It is called the trapezius due to it having the shape of a trapezoid (Figure 2–51):

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FIGURE 2–51.  Trapezius. Reproduced with permission from Anatomage.

n

This muscle is triangular and flat: n

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Origin n From the occipital bone of the skull down through C2 to the 12th thoracic vertebra Insertion n The fibers of the trapezius extend laterally to insert into the clavicle acromion and the spinous process of the scapula. Innervation n Supplied by the 11th cranial nerve, cranial nerve XI, the accessory Function n Works to rotate, move, or stabilize the scapula. When the scapulae are stabilized bilaterally, contraction of the trapezius functions to extend the neck. n Works to expand the rib cage during forced respiration

Muscles of Expiration During a passive expiration, the muscles of inspiration simply relax once inspiration is completed. When these muscles of inspiration relax, the force of recoil of the elastic rib cage, lungs, tendons of the diaphragm, and other tissues that are stretched and fully extended for inspiration begin to pull back to their original positions. This retraction of the thorax reduces the volume of the lungs and completes passive expiration. However, if greater levels of expiration are needed, then muscular contraction is used to further squeeze the thorax and push a greater volume of air out of the lungs. To continue expiration past the point of rest of the rib cage, the muscles of expiration must come into play and use active muscular contraction to continue to reduce volume of lungs past the resting point. 92

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During inspiration, the thorax is expanded along the transverse and vertical dimension. The thorax is expanded along the transverse dimension by the accessory muscles of inspiration contracting to flare the rib cage laterally and anteriorly. The thorax is expanded vertically by the elevation of the rib cage by accessory muscles of inspiration and also by the primary muscle of inspiration, the diaphragm, contracting and pulling the lungs inferiorly. During expiration, this expansion of the thorax for inspiration must be reversed to push air out of the lungs. During expiration, the thorax is reduced along these two dimensions, transverse and vertical, to return to its original resting position. During forced expiration, contraction of the muscles of the abdomen pushes the abdominal viscera (abdominal organs) against the underside of the diaphragm, thereby elevating the diaphragm past its point of rest and higher into the thorax, further reducing the vertical dimension of the lungs and expelling more air. Muscles of forced expiration also draw the ribs downward and inward past the point of rest. Muscles involved in expiration are generally categorized into the primary muscles of expiration and the accessory muscles of expiration. The primary muscles of expiration are associated with the abdomen and are involved in pushing the viscera up into the diaphragm to reduce the vertical dimension of the thorax for expiration. The accessory muscles of expiration are associated with the thorax.

Primary Muscles of Expiration The primary muscles of expiration are those associated with the abdomen (Figure 2–52). The abdomen is the section of the trunk of the body below the diaphragm and above the pelvis. The anterior abdominal muscles completely wrap the abdomen and include these four pairs of muscles: external oblique abdominis, internal oblique abdominis, transversus abdominis, and rectus abdominis. Points of Attachment for Abdominal Muscles.  Superficial to the abdominal muscles is the abdomi-

nal aponeurosis, a large, flat tendinous structure that forms the anterior wall of the abdomen (see Figure 2–56, p. 97). Deep to the abdominal aponeurosis within the abdomen are the abdominal muscles and their attachments. As there are very few skeletal points of attachment for muscles to connect to

FIGURE 2–52.  Primary muscles of expiration. Reproduced with permission from Anatomage.

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FIGURE 2–53.  Transverse view of abdominal muscles.

within the abdomen, these muscles connect to the skeleton and to each other via many and complex tendinous aponeuroses. These include the linea alba, linea semilunaris, abdominal aponeurosis, and lumbodorsal fascia: n

Anteriorly and at midline, the linea alba is a tendinous and narrow linear structure coursing from the xyphoid process of the sternum to the pubic symphysis, thereby providing an anterior and medial point of attachment for muscles of the abdomen. Proceeding laterally, the linea alba transitions into two aponeurotic sheets between which are sheathed the sections of the rectus abdominis (Figure 2–53).

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Moving laterally to the rectus abdominis, the two aponeurotic sheets of the rectus abdominis coalesce into a second linear ribbon of tendinous tissue known as the linea semilunaris (Figure 2–53). The linea semilunaris is a curved tendon on either side of the rectus abdominis. The linea semilunaris divides into three tendinous sheets, thereby providing points of attachment for three more abdominal muscles.

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Posteriorly, the fascia of the abdominal muscles transitions and coalesces to form the lumbodorsal fascia. The lumbodorsal fascia provides a point of attachment between the external and internal oblique abdominis, transversus abdominis, and vertebral column.

External Oblique Abdominis. The external oblique abdominis is the most superficial of the abdomi-

nal muscles as well as the largest (Figure 2–54): n

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Origin n The fibers of the external oblique abdominis originate on the inferior boundary of ribs 5 through 12. Insertion n Some fibers of the external oblique abdominis course from the lowest ribs and fan out inferiorly to insert onto the anterior iliac crest via what is known as the inguinal ligament, while some fibers will terminate on the abdominal aponeurosis. 94

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FIGURE 2–54.  Anterior view of external oblique abdominis. Reproduced with permission from Anatomage.

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Innervation n The external oblique abdominis has innervation supplied by anterior branches of the inferior six thoracoabdominal nerves coursing bilaterally through the intercostal spaces as well as the subcostal nerve. Function n Bilateral contraction will pull the thorax toward the abdomen and compress the abdomen for forced expiration and also for expelling contents of abdominal viscera such as during defecation and birth. n Unilateral contraction facilitates contralateral rotation of the trunk (rotation away from the side of contraction) and ipsilateral bending of the trunk (bending of the thorax toward the pelvis on the side of the contraction).

Internal Oblique Abdominis. The internal oblique abdominis muscles (Figure 2–55) are deep to the external oblique abdominis muscles but are also located laterally and ventrally on the body, as are the external oblique abdominis: n

The internal oblique abdominis is a smaller and thinner muscle than the external oblique abdominis and forms the middle layer of abdominal musculature between the external oblique abdominis and the rectus abdominis.

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The fibers of the internal oblique abdominis muscles course diagonal to and opposite to the external oblique abdominis: 95

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FIGURE 2–55.  Internal oblique abdominis. Reproduced with permission from Anatomage.

Origin n Anterior two thirds of the iliac crest via the inguinal ligament n Insertion n Courses superiorly to insert into the lower four ribs n Innervation n Innervation of the internal oblique abdominis is via the lower intercostal nerves and iliohypogastric and ilioinguinal nerves. n Function n Bilateral contraction: n Pulls the lower ribs toward the pelvis n Compresses the abdomen for forced expiration and for biological functions such as expelling the contents of abdominal viscera such as during defecation and birth n Unilateral contraction: n Assists in ipsilateral rotation of the trunk n Assists in bending of the trunk ipsilaterally toward the side of the unilateral contraction n

Transversus Abdominis. The transversus abdominis is beneath the internal oblique abdominis and is the deepest of the abdominal muscles (Figure 2–56). n

The fibers of the transversus abdominis course horizontally as is implied by the word transversus: n Origin n Inner surfaces of ribs 6 through 12 as well as from the lumbodorsal fascia, iliac crest, and inguinal ligament 96

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FIGURE 2–56.  Transversus abdominis. Reproduced with permission from Anatomage.

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Insertion n Courses laterally from origins to insert into the abdominal aponeurosis Innervation n Innervation of the transversus abdominis is via the lower intercostal nerves and iliohypogastric and ilioinguinal nerves. Function n Compresses the abdomen, contributing to forced expiration

Rectus Abdominis. The rectus abdominis (Figure 2–57) is a paired flat muscle that extends across the

anterior of the abdomen and is slung from the pubic symphysis to ribs 5, 6, and 7 and the xyphoid process: n

This muscle is divided into its paired right and left divisions at midline by the linea alba and is enclosed in an aponeurotic sheath holding it in place (Figure 2–53).

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The rectus abdominis is divided into sections of muscle by tendinous fibers creating what is known colloquially as your six-pack or abs: n

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Origin n Rectus abdominis originates at the pubic crest and pubic symphysis. Insertion n This muscle courses from the pubic crest and symphysis to insert superiorly into the xiphoid process of the sternum and the costal cartilaginous portions of ribs 5 to 7. Innervation n Motor innervation is via intercostal nerves T7 through T11; sensory innervation is via T7 through T12. Function n To bend the torso anteriorly n To pull the thorax toward the pelvis as in the action performed during sit-ups n To compress the abdomen, contributing to forced expiration 97

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FIGURE 2–57. Rectus abdominis. Reproduced with permission from Anatomage.

Accessory Muscles of Expiration The accessory muscles of expiration are associated with the thorax. These muscles include the internal intercostals, serratus posterior inferior, subcostals, transversus thoracis, innermost intercostals, and quadratus lumborum. Internal Intercostals. The internal intercostals exist in the 11 spaces between 12 ribs (Figure 2–35).

The 11 internal intercostals lie deep to the external intercostal muscles within these spaces. These muscles begin to occur at the sternum and extend posteriorly to the angle of the ribs and transition into aponeurosis prior to reaching the vertebral column: n

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Origin n Superior surfaces of the ribs Insertion n Course upward and medially to insert into the rib directly above Innervation n Innervation of the internal intercostals is accomplished via the intercostal nerves. Function n The internal intercostals, excluding the chondral portion of these muscles, work to retract the rib cage for forced expiration.

Serratus Posterior Inferior. The serratus posterior inferior is roughly the shape of a quadrilateral

(Figure 2–58). This is a muscle of the lower back: n

This muscle has lateral extensions that give the muscle its serrated appearance:

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FIGURE 2–58.  Serratus posterior inferior. Reproduced with permission from Anatomage.

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Origin n The spinal processes of the last two thoracic vertebrae (T11 to T12) and the spinal processes of the first three lumbar vertebrae (L1 to L3) Insertion n Extensions of the muscle insert into the lower four ribs lateral to the angles of these ribs Innervation n Accomplished via inferior intercostal nerves 9 through 12 Function n Stabilizes the trunk n During expiration, it is hypothesized that the serratus posterior inferior assists in retracting the rib cage.

Transversus Thoracis. The transversus thoracis (Figure 2–59) is an almost hemp leaf–shaped muscle

that exists on the inside surface of the rib cage: n

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Origin n The posterior surface of the inferior sternum Insertion n Fibers course laterally and upward to insert into the chondral portions of ribs 2 through 6. Innervation n Accomplished via the intercostal nerves Function n Contraction retracts the rib cage and resists elevation of the rib cage.

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FIGURE 2–59.  Transversus thoracis.

Subcostals. The subcostals (Figure 2–60) are a muscle group situated deep to the internal intercostals on the interior surface of the wall of the posterior thorax. The subcostals have fibers that follow the same course of the internal intercostals. Having similar course and attachments as the internal intercostals, the subcostals may assist in expiration: n

Subcostals exist primarily on the inferior inner wall of the thorax.

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The length and number of subcostals vary from person to person.

Innermost Intercostals. The innermost intercostals (Figure 2–61) exist between the ribs in the inter-

costal spaces: n

These muscles are, as the name implies, the deepest of the intercostal muscles.

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The innermost intercostals run parallel to the internal intercostals with muscle fibers originating on the superior surface of each rib and coursing up and laterally to insert into the rib above. As such, they assist in retraction of the rib cage for expiration.

Quadratus Lumborum. The quadratus lumborum is a deep posterior muscle of the abdomen (Fig-

ure 2–62). This muscle courses between the pelvis and the last rib and first four lumbar vertebrae: n

It is roughly quadrilateral in shape as is suggested by its name: n

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Origin n Aponeurotic fibers from the pelvis at the ilio-lumbar ligament and the iliac crest Insertion n Courses upward and medially to insert into the last rib and the transverse processes of the first four lumbar vertebrae 100

Anatomy of Respiration FIGURE 2–60. Subcostals.

FIGURE 2–61.  Inner intercostals.

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FIGURE 2–62. Quadratus lumborum. Reproduced with permission from Anatomage.

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Innervation n Anterior branches of the 12th thoracic nerve (T12) and the first three lumbar nerves (L1–L3) Function n Bilateral contraction of muscle pulls inferiorly on the last rib, thereby contributing to retracting the rib cage for expiration.

➤ Chapter Summary The process of exchanging gases between our bodies and the environment is respiration. As humans, we require a steady supply of oxygen to survive. In addition to successfully taking in lifesustaining oxygen from the air, we must also successfully dispose of poisonous carbon dioxide. We use our tiny air sac–like structures, called alveoli, within the lungs for the actual exchange of gases. A complete lack of oxygen to the body or portion of the body is termed anoxia. A less extreme level of oxygen deprivation is hypoxia. Inspiration is the process of pulling oxygen rich air into the lungs. Expiration is the process of pushing carbon dioxide–rich air from inside the lungs back into the environment. The body completes respiration automatically with no volitional or cognitive effort to ensure the body is constantly and appropriately inspiring oxygen and expiring carbon dioxide. However, the process of respiration can be placed under volitional control, and that allows for the production of voice and speech using expiratory air. The tissues that provide the framework for respiration can be divided into the soft tissues known as the visceral thorax and the bones of the thorax known as the bony thorax. The bony thorax includes the vertebral column, rib cage, and pectoral girdle, and that provides structure to the thorax and support to soft tissues of the thorax.

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The vertebral column consists of 32 or 33 individual bones known as vertebrae resting on top of each other that form the framework for the superior portion of the skeleton. There are five types of vertebrae that make up the human vertebral column. From superior to inferior (Figure 2–3), these are the seven cervical vertebrae, the 12 thoracic vertebrae, the five lumbar vertebrae, the four to five fused sacral vertebrae, and the three to five fused coccygeal vertebrae. The cervical, thoracic, and lumbar vertebrae are individual bones that articulate and connect with each other via the cartilaginous discs and ligaments between them. The anterior cylindrical mass of a vertebra is the corpus or body, and this is the weightbearing portion of the vertebra. On either side of the corpus, two projections known as the pedicles attach to the posterior section of the vertebra. These pedicles fuse with posterior plates known as laminae. From the laminae, the transverse processes are bony projections that project laterally. At midline, the laminae come together and project posteriorly to form the spinous process. The pedicles and laminae fuse to form a foramen (a hole or space) against the corpus. This is the vertebral foramen, and it protects and houses the spinal cord. The cervical, thoracic, and lumber vertebrae have lateral openings that are formed between the vertebrae. These are the intervertebral foramina. The cervical vertebrae bear the least amount of weight of any other section of the vertebral column, since they bear only the weight of the head and neck. Because of this, the cervical vertebrae are noticeably smaller and more delicately structured than those vertebrae in other inferior sections of the vertebral column. The first cervical vertebra (C1) is known as the atlas. The second cervical vertebra (C2) is known as the axis. This name reflects the second cervical vertebra’s function of being the structure on which the atlas articulates and rotates. The thoracic vertebrae are essential to the process of respiration by providing posterior attachment points for the rib cage. The lumbar vertebrae are located beneath the thoracic vertebrae and are the vertebrae of our lower backs and bear most of the weight of the upper body. The sacral vertebrae are the four or five fused vertebrae that form a single triangular bone known as the sacrum. The inferior-most portion of the vertebral column projecting inferiorly from the sacrum is the coccyx, or the coccygeal vertebrae. These are three to five vertebrae fused into a single mass. The sternum is the prominent anterior and midline structure of the thorax that provides a point of attachment for the clavicles (collarbones) and for many ribs. The sternum is composed of the manubrium sterni, the corpus (or body), and the xiphoid (or ensiform) process. The rib cage creates the structure of the thoracic cavity and provides protection for the lungs. The rib cage is also the framework by which expansion and contraction of the lungs for respiration are possible. The rib cage is composed of 12 pairs of ribs. All the ribs originate posteriorly at the thoracic vertebrae. Ribs 1 through 10 attach anteriorly directly or indirectly to the sternum. The rib cage is composed of three types of ribs: vertebrosternal, vertebrochondral, and vertebral ribs. The vertebrosternal ribs articulate directly with the thoracic vertebrae posteriorly and the sternum in the anterior. The vertebrochondral ribs attach directly to the thoracic vertebrae posteriorly and anteriorly attach to the costal cartilage of rib 7. The vertebral ribs have posterior attachments at the thoracic vertebrae but are about half the length of the other ribs and have no anterior point of attachment. Ribs 1, 10, 11, and 12 each articulate posteriorly to only a single corresponding thoracic vertebra. Ribs 2 through 9 each articulate posteriorly to two thoracic vertebrae. The rib cage is elevated and expanded during inspiration in the anteroposterior fashion by the muscles of inspiration.

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The pelvic girdle is the bony portions of the lower regions of the abdomen, also often referred to as the bony pelvis. The pelvic girdle provides points of origin for most of the abdominal muscles. The pectoral girdle consists of the clavicle and scapula and is the point of origin of some muscles of respiration. The only skeletal point of connection for the pectoral girdle is the sternoclavicular joint, the point at which the clavicle articulates with the sternum. The visceral thorax is the major organs and soft tissues of the thorax, which perform all manner of life-sustaining functions. Included in this are the heart, lungs, respiratory passages, and associated connective tissue and muscles. Those tissues and structures that are directly responsible for exchange of gases and through which air moves during the process of respiration are the respiratory passages. The upper respiratory tract includes, from superior to inferior, the nasal and oral cavities, the pharynx, and the larynx. The lower respiratory tract is the respiratory passages below the larynx; from superior to inferior these include the trachea and all branches of the bronchial tree down to the alveoli. The lungs are the primary organs of respiration and house the major passages and structures that allow the human body to absorb oxygen and release carbon dioxide. The right lung is larger than the left lung. The right lung has three distinct lobes. These are known as the superior, middle, and inferior lobes. The left lung has only two lobes, inferior and superior. The lungs are held fast within the thorax via a double layer of tissue known as the pleural membranes. The pleural membranes allow for the smooth and gliding expansion of the lungs with the lowering of the diaphragm and expansion of the thorax. The cavity between these two layers of pleurae is known as the intrapleural space. A lubricating secretion known as surfactant exists between the pleural membranes. The vacuum that exists in the intrapleural space causes the lungs to follow and move with the rib cage when the thorax expands or retracts. The vacuum state creating the connection between the visceral and parietal pleura is known as the pleural linkage. The last few divisions of the bronchial tree lead to areas known as respiratory zones that contain alveoli and are where the exchange of gases actually occurs. Each alveolus is enwrapped in capillaries. It is by virtue of this intimate relationship between the alveoli and blood supply via the capillaries that allows gas exchange to occur. The alveoli allow for free exchange of molecules of oxygen and carbon dioxide between the air in the alveoli and the blood in the capillaries; this exchange, oxygen in and carbon dioxide out, is the actual process of respiration. Quiet respiration occurs naturally as a person is breathing softly with the body exerting little physical effort and includes quiet inspiration and passive expiration. In forced respiration, additional muscular activity is used to increase the amount of air inspired and expired and to increase the rate of respiration and includes forced inspiration and forced expiration. The diaphragm is the primary muscle of inspiration and is a large, dome-shaped muscle that creates the anatomical division between the thoracic cavity and the abdominal cavity. Upon contraction, the diaphragm expands the thoracic cavity inferiorly. Muscles that can elevate the rib cage can be engaged for forced inspiration and are referred to as the accessory muscles of inspiration. Accessory muscles of inspiration of the rib cage include the external intercostals and the chondral portion of the internal intercostals. Accessory muscles of inspiration of the chest include the pectoralis major, pectoralis minor, serratus anterior, and the subclavius. Accessory muscles of inspiration of the neck include the scalenes (anterior, medial, and posterior), and sternocleidomastoid. Accessory muscles of inspiration

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➤ Reference Amador, C., & Varacallo, M. (2020). Anatomy, thorax, bronchial. StatPearls.

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of the back include the serratus posterior superior, levator costarum (brevis and longis), levator scapulae, latissimus dorsi, and trapezius. If greater levels of expiration are needed past a passive expiration, then muscular contraction is used to further squeeze the thorax and push a greater volume of air out of the lungs. To continue expiration past the point of rest of the rib cage, the muscles of expiration must come into play. The primary muscles of expiration are those associated with the abdomen and include the external oblique abdominis, internal oblique abdominis, transversus abdominis, and rectus abdominis. The accessory muscles of expiration are associated with the thorax and include the internal intercostals, serratus posterior inferior, subcostals, transversus thoracis, innermost intercostals, and quadratus lumborum.

3 Physiology of Respiration

➤ Learning Objectives Upon completion of this chapter, students will be able to: n

Summarize the physiological process of respiration.

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Explain the neural origins of respiration.

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Explain the mechanical process of respiration and physical forces involved in inspiration and expiration.

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Describe lung volumes and capacities.

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Identify changes in respiration that occur with age.

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Explain the process of gas exchange during respiration at the molecular level.

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Identify the methods of measures of respiration.

➤ Introduction to Physiology of Respiration Knowledge of the process and physiology of respiration is important to the speech-language pathologist because it is the respiratory system that provides the energy for the production of voice and speech. Often, the speech-language pathologist must provide therapy to strengthen the inspiratory and/or expiratory muscles of the respiratory system to increase an individual’s expiratory volume and expiratory pressure to restore the individual’s ability to produce voice. Respiration is the exchange of gases between an organism and the environment. In humans, this is specifically our extraction of oxygen from the atmosphere and our releasing of carbon dioxide back into the atmosphere. This occurs through our constant exchange of air with the environment in the form of inspiration and expiration. Inspiration is the pulling of air into the lungs, while expiration is the pushing 107

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of air out of the lungs. Respiration is often measured in cycles. One inspiration and one expiration are known as one cycle of respiration. There are different patterns of respiration that are used to meet different physiological or communicative needs. Some of the terms used moving forward in this chapter are similar to one another. See Figure 3–1 for a flowchart to help keep terms associated with vegetative respiration differentiated. Vegetative respiration is the automatic (i.e., unconscious) respiration to meet our bodies’ needs for the intake of oxygen and the release of carbon dioxide. Vegetative respiration patterns can be quiet or forced respiration (Figure 3–1). Quiet respiration is respiration to meet the respiratory needs of the body at rest and is also known as eupnea. Healthy adults at rest will display respiratory rates of around 12 to 17 quiet respiratory breaths per minute (i.e., cycles of respiration per minute). If timed, the phases of inspiration and expiration during quiet respiration are almost equal in length. A quiet inspiration constitutes 40% of the cycle of respiration, while the accompanying expiration takes a slightly longer amount of time and constitutes the remaining 60% of the respiratory cycle. For instance, an average cycle of quiet respiration for a 25-year-old man is 4.39 seconds (Hoit & Hixon, 1987). Therefore, approximately 1.75 seconds of the quiet respiratory cycle is spent during the inspiratory phase, while the expiratory phase is approximately 2.63 seconds. Vegetative respiration, quiet or forced, occurs automatically, and the neural signals for these breathing patterns originate from the brainstem where many life-sustaining functions of the bodies are generated.

FIGURE 3–1.  Patterns of vegetative respiration.

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Respiration originates specifically in the respiratory center (Figure 3–2), which is a specialized neural network located within the medulla and pons of the brainstem. Neurons in the respiratory center receive information from various parts of the body and brain regarding oxygen and carbon dioxide levels in the body. The respiratory center uses this information to appropriately manage the rhythm, rate, and depth of respiration to ensure appropriate homeostasis (balance) of oxygen and carbon dioxide in the arterial system. If the body is not getting enough oxygen during quiet respiration, the respiratory center generates neural signals to increase the speed and volume of respiration to take in larger amounts of air faster and acquire greater levels of oxygen. This requires the activation of more muscles than quiet respiration. This more active and labored breathing pattern is forced respiration or hyperpnea and is normal during exercise (Figure 3–1). Once the body is receiving enough oxygen, the respiratory center decreases the speed and volume of breathing, and the body ceases forced respiration and returns to quiet respiration. Children and infants have faster rates of quiet respiration than do adults. In part, this is due to the smaller lungs of children and infants, which require a faster exchange of air in the lungs to maintain appropriate oxygen levels than adult lungs, which are capable of holding a greater volume of air. Tidal volume is the amount of air inspired and expired in a cycle of respiration. The tidal volume and rate of respiration during quiet respiration change as the body grows and ages. Standard norms are cited as follows for various age groups: Male children at 7 years of age have mean tidal volumes during quiet respiration of 200 ml with 18.91 breaths per minute, raising to 260 ml at age 10 years, 39 ml at age 13 years, and begin to approximate adult tidal volumes with a mean of 560 ml at age 16 years (Hoit et al., 1990). n Female children at 7 years of age have mean tidal volumes during quiet respiration of 190 ml, raising to 280 ml at 10 years of age, 390 ml at 13 years of age, and begin to approximate adult tidal volumes with a mean of 410 ml at age 16 years (Hoit et al., 1990). Physiology of Respiration

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FIGURE 3–2.  Image of respiratory center. Used with permission from Anatomage.

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n

Males of ages from 25 to 75 years have mean tidal volumes of 500 to 700 ml of tidal volume during quiet respiration with 13.7 to 15.6 breaths per minute (Hoit & Hixon, 1987).

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Females of ages from 25 to 75 years have mean tidal volumes of 500 to 600 ml of tidal volume during quiet respiration with 11.7 to 13.1 breaths per minute (Hoit et al., 1989).

As long as there is no physical exertion, quiet respiration is quiet inspiration and passive expiration. However, with increased physical exertion, the body’s need for oxygen increases, and respiration becomes more labor intensive and engages more muscles than just the diaphragm. As this occurs, inspiration ceases to be quiet and becomes forced to increase the volume of air inspired. Also, expiration becomes forced to more speedily and more deeply empty the lungs of air. In contrast to vegetative respiration, forced or quiet, speech breathing is a forced respiration pattern that is used to volitionally commandeer the respiratory system to produce speech. This is adduction of the vocal folds during expiration to generate phonation as well as varying constriction of the expiratory airstream through the vocal tract for articulation of phonemes. During speech, the patterns of activation of the muscles of the respiratory system change to accommodate the physiological needs of speech production. These are largely changes in the depth and speed of inspiration and expiration, which bring different muscle groups into play: n

Changes in the volume and rate of respiration from quiet respiration to speech breathing require the activation of more muscles of respiration. As discussed in Chapter 2, the diaphragm is the primary muscle activated for quiet respiration. During tasks such as speaking that require greater levels of tidal respiration, the accessory muscles of inspiration and muscles of expiration, such as those associated with the elevation/expansion and depression/retraction of the rib cage, are engaged to increase volume of air inspired and expired and to carefully control expiration for speech production.

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The inspiratory phase for speech breathing has a shorter duration and greater inspiratory volumes than inspiration during quiet respiration (Hixon, 1987; Hixon et al., 1973). The inspiratory phase is approximately 10% of a breath cycle during speech.

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The expiratory phase of speech breathing is characterized by longer durations and greater expiratory volumes than the expiratory phase of quiet respiration (Hixon, 1987; Hixon et al., 1973). The expiratory phase is approximately 90% of a breath cycle during production of speech.

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During quiet respiration, the expiratory airstream is directed through the nose, while during speech breathing, the expiratory airstream is directed primarily through the oral cavity for the creation of speech.

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In summary, while speaking, individuals n

inspire more quickly to maintain normal rate of speech

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inspire greater volumes of air in order to produce appropriate length of utterance

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expire greater volumes of air to maintain speech production

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adduct the vocal folds intermittently over the expiratory airstream at the level of the larynx for the production of phonation direct expiration through the mouth to power articulation and speech production expire more slowly as expiratory pressure and the expiratory airstream are being used to power phonation at the vocal folds and articulation in the oral cavity add active expiratory muscle contraction to the natural recoil of the thorax to maintain relatively constant expiratory pressure 110

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During a high-volume expiration for speech breathing, the muscles of inspiration slowly relax from the point of maximum inspiration to allow for a controlled and slowed rebound of the thorax, which allows the expiratory airstream to be controlled for speaking. This slow relaxation of the muscles of inspiration to check the retraction of the thorax and control the expiratory airstream for speech is known as inspiratory checking. Inspiratory checking is one factor that allows the expiratory airstream to be slowed and carefully regulated to maintain appropriate pressure beneath the vocal folds (subglottal pressure) for the production of phonation. Another factor that allows for the subglottal pressure to be carefully maintained is the controlled contraction of the muscles of expiration at the onset of the expiration for phonation. This contraction of expiratory muscles as well as inspiratory checking allow for appropriate maintenance of subglottal pressure for phonation and speech. Inspiratory checking allows for controlled retraction of the thorax to its natural point of rest. However, humans are capable of continued expiration after the thorax reaches its neutral point where passive forces such as elasticity of tissues are no longer acting to retract the thorax. For this continued expiration, the muscles of expiration are further engaged, further depressing/retracting the rib cage, and compressing the abdomen to further elevate the diaphragm. This forced expiration past the thoracic point of rest can be utilized for speech breathing or for vegetative breathing. Inspiratory checking to slow expiration and forced expiration to continue expiration past the point of rest of the thorax are partly why the length of expiration during speech breathing is longer than expiration during vegetative respiration. During vegetative respiration, the thorax rebounds to resting position quickly and unopposed.

During respiration, the thorax expands and retracts in three dimensions: anteroposterior, vertical, and transverse. This expansion and retraction of the thorax and movement of the diaphragm is the action that creates inspiration and expiration. There are multiple forces acting on the body during respiration that are responsible for and affect this cycle of expansion and retraction. These include the active force of muscular contraction mostly involved in inspiration as well as passive forces that contribute mostly to expiration.

Active Force of Respiration n

The active force of respiration is muscular contraction. During quiet inspiration this includes contraction of the diaphragm only. During forced inspiration, this includes the contraction of the diaphragm and the accessory muscles of inspiration acting for thoracic expansion. During forced expiration, this includes contraction of the muscles of expiration that actively compress the thorax, or retract the rib cage, to push more air out of the lungs than is typically expired on a passive expiration. This also includes the contraction of the muscles of the abdomen that, when engaged, squeeze abdominal viscera superiorly further assisting in elevation of the diaphragm for forced expiration.

Passive Forces of Respiration n

Passive forces of respiration involve gravity and the recoil forces of elastic tissues.

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Gravity will affect respiration differently depending on the posture/position of the body. Therefore, it is necessary when discussing the effects of gravity on respiration to consider the factor of body position and posture and to remember that appropriate posture is paramount to maintaining appropriate respiratory capacity for speech. 111

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➤ Forces of Respiration

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n

When a person is in standing position, gravity is pulling the base of the lungs inferiorly and is also inferiorly displacing abdominal viscera. The outcome of both of these actions is to increase the ease with which the inferior expansion of the thorax by contraction of the diaphragm is completed, thereby assisting inspiration. During expiration while standing upright, the force of gravity will work against the passive superior retraction of the diaphragm and lungs, thereby working somewhat against expiration. During more active labored respiration that is utilizing greater levels of thoracic elevation, gravity will work against elevation of the thorax for inspiration but will facilitate inferior retraction of the thorax during expiration. n While in a supine (lying face up) position, the force of gravity is pulling down on the rib cage. In this position, gravity is flattening the abdominal viscera within the body, which pushes it rostrally (toward the head) against the diaphragm. Both of these effects of gravity on the body in a supine position make expansion of the thorax for inspiration more difficult while facilitating retraction of the thorax for expiration. n Tissue elasticity is the degree to which the fibers of the body, once deformed, are subsequently able to passively retract to their original position. n The passive force of tissue elasticity is associated with the retraction of the thorax after thoracic extension/expansion in the three dimensions mentioned earlier. All the body tissues that are stretched and distended during expansion of the thorax by the muscles of inspiration will pull themselves back to their resting position once the muscles of inspiration relax. n This elasticity of the lungs, rib cage, and associated muscles and tissues follows Newton’s third law of motion. This law states that for every action there is an equal and opposite reaction. Simply stated, the thorax is stretched and distended to accommodate thoracic expansion for inspiration. The greater the degree of expansion of the thorax, the greater the degree to which the elastic tissues of the thorax have to be stretched and distended. And, like a stretched rubber band, those tissues now possess potential energy ready to be released. Once the active force of muscular contraction of muscles of inspiration has ceased expansion of the thorax, the elasticity of the tissues of the thorax will retract the thorax back to a resting position, compressing the lungs and expelling air.

Pressures Involved in Respiration The aerodynamic and muscular process of respiration involves the interaction and interplay of various pressures. Before describing the role and functions of these pressures in the process of respiration, let us define them: n

Alveolar pressure is the air pressure within the alveoli of the lungs. During inspiration, alveolar pressure is negative. Alveolar pressure changes to positive for expiration. n Atmospheric pressure is the air pressure on the surface of the earth. More specifically, it is the amount of pressure created by gravity’s pull on the air on the surface of the earth. You live within atmospheric pressure, but it is not felt because the human body is adapted to it. Atmospheric pressure is relatively constant during respiration; it does not change in any way significant enough to affect respiration. Rather, during respiration, the muscles of the body move the thorax to change alveolar pressure to complete inspiration and expiration within a stable atmospheric pressure. n Intrapleural pressure is the pressure that exists within the pleural linkage, between the visceral pleura and parietal pleura, that connects the lungs to the interior walls of the thorax: n Negative intrapleural pressure holds a tension between the lungs and the thorax. 112

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As the thorax is expanded for inspiration, intrapleural pressure becomes more negative until it pulls the lungs along via this suction to follow thoracic expansion (Figure 3–3). When inspiration ceases and the thorax is released by now relaxing muscles to recoil passively into a rest position, intrapleural pressure becomes less negative (more positive), allowing the lungs to follow thoracic retraction (Figure 3–3). In this momentary position prior to the re-initiation of the inspiratory process, the lungs are held in tension with the thorax by negative intrapleural pressure. In this moment, the thorax is holding the lungs in a slightly expanded position while the lungs are pulling the thorax into a slightly retracted position.

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Intraoral pressure is the air pressure within the oral cavity.

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Subglottal pressure is the air pressure below the glottis, the space between the vocal folds. Subglottal air pressure is the air pressure that drives phonation at the vocal folds. Subglottal pressure varies according to the frequency and intensity demands of speech. For example, your subglottal pressure is much lower when speaking quietly than when raising your voice.

➤ Physics of Respiration/Breathing To understand how inspiration and expiration occur, one must understand Boyle’s law. Before one understands Boyle’s law, one must first understand air pressure. Air pressure within a container is the amount of force that is being exerted by the air that is inside the container on the inside surface of the container. Molecules of air within a closed container exhibit Brownian motion: random, high-speed, and constant motion in which they are constantly colliding with each other and the walls of the container (Figure 3–4). It is the cumulative force of all these tiny individual collisions between the molecules 113

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FIGURE 3–3.  Changes in intrapleural pressure.

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FIGURE 3–4.  Brownian motion.

of air within the container and the walls of the container that creates the force pushing on the walls of the container. The more often air molecules are colliding with the interior of the container, the greater the air pressure will be within that container. The less often air molecules are colliding with the interior of the container, the less the air pressure will be within that container. Boyle’s law describes the relationship between volume of a closed container and the air pressure within the container. Boyle’s law states that given a constant temperature, if the volume of a container is decreased, air pressure within that container increases, whereas if the volume of a container is increased, air pressure within the container decreases. Looking at the two containers in Figure 3–5, one container has a larger volume, while the other has a smaller volume. Both containers have the same number of molecules of air within. The larger container has more room within, and the molecules of air are well dispersed. The smaller container has less room, and the molecules are squeezed closer to themselves and closer to the walls of the smaller container. The molecules in the larger container will be colliding with the walls of that container less often than the same number of molecules in the smaller container. Therefore, the larger container will have a lower amount of air pressure within than the smaller container that will have a higher level of air pressure. Furthermore, if one imagines the larger container increasing in size with the same number of molecules inside, then the air molecules will keep being pulled farther apart, colliding less often with the interior walls of the container, and air pressure within the container will consequently continue to decrease. If one imagines the smaller container growing smaller with the same number of air molecules inside, the air molecules will keep getting pushed closer together, colliding more often with the walls of the container, and air pressure within the container will consequently continue to increase. Boyle’s law allows us to understand the movement of air in and out of the lungs: 114

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During inspiration, muscular contraction such as by the diaphragm (Figure 3–6) expands the thorax, which increases the volume of the lungs. Boyle’s law dictates that if volume of a container increases, then air pressure within that container decreases. As the lungs are a

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FIGURE 3–5.  Boyle’s law.

FIGURE 3–6.  Diaphragm movement during inhalation and exhalation.

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container of air that has increased in volume, alveolar pressure decreases below atmospheric pressure. Air always moves from areas of higher pressure to lower pressure. Therefore, a decrease in alveolar pressure causes molecules of air to move from the area of more positive pressure (the atmosphere) into the area of lesser pressure (the alveoli, the lungs). As the lungs continue to increase in volume, negative pressure created by this increase in volume will continue to pull air into the lungs. This is the process of inspiration (Figure 3–6). When the lungs cease expansion, alveolar pressure will equal atmospheric pressure, and inspiration will stop. n Retraction of the thorax such as by passive superior retraction of the diaphragm and lungs, (Figure 3–6) will begin decreasing the volume of the lungs. Boyle’s law dictates that if the volume of a container decreases, then air pressure within that container increases. As the lungs are a container of air that is now decreasing in volume, alveolar pressure increases above atmospheric pressure. Air always moves from areas of higher pressure to lower pressure. Therefore, an increase in alveolar pressure causes molecules of air to move from the area of more positive pressure (the alveoli, the lungs) into the area of lesser pressure (the atmosphere). As the lungs continue to decrease in volume, the positive pressure created by this decrease in volume will continue to push air out of the lungs back into the environment. This is expiration (Figure 3–6). This continues until the lungs cease retraction, and expansion of the lungs for inspiration begins again.

Understanding the Mechanical Cycle of Respiration Now that we covered the anatomy of respiration in Chapter 2 as well as forces and pressures involved in respiration, let’s pull all these concepts together for a step-by-step discussion of how these many things interact for successful respiration.

Quiet Respiration:  Quiet Inspiration/Passive Expiration During quiet respiration, the primary muscle at work is the diaphragm. During a quiet inspiration, the diaphragm contracts, causing it to flatten downward out of its dome shape. As the diaphragm lowers, it elongates the thoracic cavity inferiorly, and in doing so, the lungs are elongated inferiorly as well. The lungs are connected to the interior thoracic wall via the pleural linkage that, by virtue of the negative pressure that exists between the pleural layers, pulls the lungs inferiorly along with the diaphragm as the diaphragm contracts. The volume of the lungs is increased as they are expanded inferiorly by the downward pull of the diaphragm. As the volume of the lungs increases, alveolar pressure decreases below atmospheric pressure. As air always flows from areas of higher pressure to areas of lower pressure, air moves from the atmosphere with more positive pressure into the lungs where alveolar pressure has dropped below atmospheric pressure and become negative. This inspiration of air into the lungs will continue as long as the diaphragm continues to expand the volume of the lungs. Once the diaphragm reaches its point of maximal excursion, it will cease lowering, that will then cease the inferior expansion of the lungs, and alveolar pressure will equalize momentarily with atmospheric pressure until expiration begins. The process of passive expiration begins as the diaphragm relaxes. The relaxation of the diaphragm allows the passive expiratory force of tissue elasticity to come into play. With the relaxation of the diaphragm, the lungs and diaphragm will begin to retract to their original neutral position of rest. The inferiorly displaced contents of the abdomen are now free to shift superiorly against the diaphragm, pushing the diaphragm superiorly toward its original neutral position of rest. As the diaphragm retracts, the lungs retract as well. This recoil of the lungs reduces volume of the lungs. The reduction of lung 116

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volume increases alveolar pressure above atmospheric pressure. Since air moves from areas of higher pressure to areas of lower pressure, this increase in alveolar pressure moves air from the lungs into the environment. This process of expiration continues until the thorax and lungs reach the neutral position at rest, at which point alveolar pressure momentarily is equal to atmospheric pressure.

During physical exertion, the body needs to take in more oxygen more quickly from the environment than can be accomplished during quiet respiration. During forced inspiration, the accessory muscles of inspiration, such as the external intercostals, chondral portion of the internal intercostals, and all related muscles of the chest and neck, as well as the diaphragm, contract to increase the volume of air inspired and the speed with which it is inspired. As the diaphragm is contracting and lowering to expand the lungs inferiorly, the accessory muscles of inspiration are elevating the rib cage to expand the thorax superiorly and anteriorly and flaring the ribs laterally to expand the thorax in the transverse dimension. The lungs are connected to the interior thoracic wall via the pleural linkage, which, by virtue of the negative pressure that exists between the pleural layers, pulls the lungs inferiorly along with the diaphragm, as well as pulls the lungs superiorly, anteriorly, and laterally with superior and lateral expansion of the rib cage. The volume of the lungs is increased as they are expanded. As the volume of the lungs increases, alveolar pressure decreases below atmospheric pressure. As air always flows from areas of higher pressure to areas of lower pressure, air moves from the atmosphere with the more positive pressure into the lungs where alveolar pressure has become negative. This inspiration of air into the lungs will continue as long as the accessory muscles of inspiration and the diaphragm continue to expand the volume of the lungs. Once these muscles bring the thorax to its point of maximal excursion, it will cease expanding, and that will cease the expansion of lung volume. At this point, forced inspiration ends, and alveolar pressure will equalize momentarily with atmospheric pressure until forced expiration begins. The process of forced expiration begins as the muscles of inspiration relax and the muscles of expiration, such as the abdominal muscles and the internal intercostals, activate. The relaxation of the accessory muscles of inspiration frees the thorax to retract back to a position of rest. The muscles of expiration contract to retract the thorax and diaphragm more quickly than is possible with only passive forces. The retraction of the thorax and diaphragm reduces the volume of the lungs. This reduction in lung volume raises alveolar pressure above atmospheric pressure. The muscles of expiration are able to retract the thorax beyond the neutral point of rest in order to push greater volumes of air out of the lungs than during a passive expiration. Since air moves from areas of higher pressure to areas of lower pressure, this increase in alveolar pressure moves air from the lungs into the environment. This process of forced expiration continues until the individual has reached the desired point of maximal expiration and retraction of the thorax ceases, at which point alveolar pressure momentarily is equal to atmospheric pressure. When the muscles of expiration relax, the thorax is freed to begin again the process of inspiration.

➤ Lung Volumes and Capacities The lung volumes are individual and separate divisions of the total amount of air that the lungs are capable of containing. Lung volumes are measured in liters or milliliters. There are four individual lung volumes that, when added together, constitute all the air that the lungs are capable of containing (Figure 3–7): 117

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Forced Respiration:  Forced Inspiration/Forced Expiration

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FIGURE 3–7.  Lung volumes and respiratory capacities.

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The volume of air that is inspired and expired during a cycle of quiet respiration is known as tidal volume (TV) (Figure 3–7). A tidal inspiration is the amount of air pulled into the lungs during an inspiration. A tidal expiration is the amount of air expelled from the lungs during an expiration. However, the amount of air inspired and expired tidally varies according to the level of physical exertion an individual is engaged in. An individual expending more physical effort, using forced respiration, will be tidally inspiring and expiring larger volumes than an individual sitting quietly. Respiration patterns discussed earlier cited normative data for quiet TV.

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If an individual decides to pull more air into the lungs than is usually inspired during a quiet tidal inspiration, the maximum and additional quantity of air that can be inspired is the inspiratory reserve volume (IRV) (Figure 3–7). IRV is the maximal amount of air that can be inspired after a tidal inspiration. As an individual increases the amount of TV during respiration, for instance with exercise, the amount of IRV decreases. Once the individual is inspiring as much air as possible, the inspiratory reserve will become zero, as no additional air can be inspired.

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If an individual decides to expire more air at the end of a tidal expiration, that maximum volume of air that can be expired is the expiratory reserve volume (ERV) (Figure 3–7). ERV is the maximal amount of air that can be expired after a tidal expiration. As tidal expiration increases, ERV decreases until TV is as large as possible, at which point ERV will be zero as no additional air can be expired.

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The ERV for a 25-year-old male is usually around 1,730 ml (Hoit & Hixon, 1987) and around 1,320 ml for a 25-year-old female (Hoit et al., 1989). 118

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After the ERV has been squeezed out of the lungs in a maximal expiration, there will still be an amount of air remaining in the lungs. As humans, we cannot entirely empty our lungs of air. This amount of air that is retained in the lungs and can never be expired is the residual volume (RV) (Figure 3–7). n

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Since RV cannot be expired, it cannot be used to generate expiration to speak with. However, it plays an important role in always keeping the alveoli in contact with air so that the body continues with the process of gas exchange even during expiration. In other words, RV ensures that the body is continuously pulling oxygen from the environment and releasing carbon dioxide, even at moments when exchange of air is not happening, or after a full expiration. The amount of air that exists in the passageways of the lungs (such as the trachea, bronchi, bronchioles) that are not directly involved in gas exchange is known as dead air and is included as a part of RV.

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As the name implies, total lung capacity (TLC) is the amount of all air present in the lungs after a full inspiration. TLC is all the lung volumes added together (TLC = TV + ERV + IRV + RV) (Figure 3–7). TLC increases as the body grows through puberty. The TLC of a 25-year-old male is around 6,740 ml (Hoit & Hixon, 1987) and around 5,030 ml for a 25-year-old female (Hoit et al., 1989).

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The amount of air in the lungs after a passive expiration is the functional residual capacity (FRC) (Figure 3–7). FRC is calculated by adding RV to ERV (FRC = RV + ERV). The FRC for a 25-year-old male is around 3,120 ml (Hoit & Hixon, 1987) and around 2,420 ml for a 25-year-old female (Hoit et al., 1989).

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The total amount of air that can be inspired from the point of a tidal expiration is the inspiratory capacity (IC) (Figure 3–7). IC is calculated by adding TV to IRV (IC = TV + IRV).

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Vital capacity (VC) is the amount of air you can expire after a maximal inspiration (Figure 3–7). Therefore, VC will equal ERV plus TV plus IRV (VC = ERV + TV + IRV). VC tends to be the most commonly used respiratory capacity among speech-language pathologists. This is usually because it is the maximal amount of expiratory airflow that you have available to you to generate voice and speech. n

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VC tends to be a function of body size. Those individuals who are larger tend to have greater VCs. Children have smaller VCs than adults, and males have average larger VCs than females. VC for a 25-year-old male is around 5,350 ml (Hoit & Hixon, 1987) and around 3,930 ML for a 25-year-old female (Hoit et al., 1989). The volume of VC in the lungs at rest is approximately 38%. Also, TV constitutes approximately 15% of VC (Rahn et al., 1943). VC can be affected by body position. An upright position tends to increase VC. While lying in the supine or prone position, VC tends to decrease. VC can also be negatively affected by disease. Abnormal reduction of VC is a significant indicator of the presence and severity of pulmonary disease or neuromuscular disease and possible respiratory failure. 119

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Whereas lung volumes interact with one other but do not overlap, respiratory capacities are combinations of two or more lung volumes. Respiratory capacities are used to quantify certain physiological limits of the body.

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➤ Changes in Respiration With Advanced Age As discussed earlier, TV and RV increase with age from childhood to adulthood as the lungs grow and expand. The lungs reach mature development between the ages of 20 and 25 years. After this age, continued aging is associated with an overall progressive decline in respiratory function. In normal healthy aging, these changes do not impair functional respiration. This progressive decline is associated with four primary changes with age: n

Lung tissue becomes less elastic:  The lung tissue that holds airways open becomes less elastic. This means the airways stay less dilated and allow less airflow. Smaller, more peripheral airways may collapse, entirely sealing off their alveoli. This reduces the amount of functional gas exchange surface, which contributes to conditions such as chronic obstructive pulmonary disease (Janssens et al., 1999). n Thorax becomes stiffer:  The tissues of the thoracic walls also become stiffer and less compliant with advancing age. This increased stiffness in the tissues of the chest wall raises the amount of energy the body is required to expend in the expansion and retraction of the thorax during respiration. n Muscles become weaker:  Like all muscles of the body, the muscles of inspiration and expiration atrophy and lose strength with age. All these changes culminate in a situation where the muscles of respiration have to work harder, with less effective lung tissue, than when younger to achieve the same degree of gas exchange. n Alveolar gas exchange becomes less efficient:  Gas exchange efficiency at the level of the alveoli peaks in a person’s early 20s and then becomes less efficient as an individual ages. This occurs for a number of reasons. If a person smokes or their respiratory system is exposed to toxins, this causes the destruction of alveoli, which reduces the available surface area available for the process of gas exchange. The closure of small airways due to loss of elasticity of the lungs may also reduce alveolar surface area available for gas exchange. Also, as the heart and cardiovascular system experience age-related decline becoming stiffer and less compliant, the capillaries surrounding the alveoli become less capable at allowing the exchange of gas molecules across capillary walls and are less efficient at exporting freshly oxygenated blood from the lungs to the rest of the body. As respiratory function is affected by normal changes in aging, so are lung volumes and capacities: n

With weakened muscles of respiration, a stiffer chest wall, and less elastic lung tissue, the amount of air that can be voluntarily expired after a quiet inspiration, ERV, declines with age. As ERV declines, this change will impact other lung volumes and capacities. n As ERV declines, the amount of air that stays within the lungs, the RV, increases as less air is able to be pushed out of the lungs than before (Frank et al., 1957). Past the age of peak respiratory function, around the age of 20 years, RV increases 100 to 200 milliliters per year. n VC peaks when a person is in their early 20s at about 3,800 ml of air and progressively declines thereafter with age around 200 to 300 ml every 10 years for healthy nonsmokers (American Lung Association, 2019). n Overall TLC declines slightly with normal age but not to a degree that impairs respiration.

➤ Measurement of Respiration and Instrumentation A complete discussion of the various methods, instrumentation, and reasons behind measurement of respiration are beyond the scope of this text. However, it is important for the student of speech-language 120

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pathology to connect previously discussed physiology of respiration to information regarding measurement and assessment of respiration. Respiration is usually measured along the parameters of rate, pressure, and volume.

Measuring Rate n

Rate of respiration is usually measured in cycles of respiration per minute.

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Rate of respiration is measured easily enough by counting the number of cycles of respiration a person completes within 1 minute and comparing that to normative data.

Measuring Pressure Manometry is the measurement of pressure within the respiratory system using a manometer.

n A n

manometer is a simple device that is used to measure the pressure of expiration.

The most basic manometer is known as a U-tube manometer. This simple device is a tube in a shape of a U with water sitting in the base of the U (Figure 3–8). When the subject expires into one end of the tube, the water that is sitting in the base of the tube is pushed upward toward the other end of the tube. The greater the expiratory pressure applied (the more forcefully the

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FIGURE 3–8.  U-tube manometer used to measure respiratory pressure.

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subject expires), the higher is the displacement of the column of water within the tube of the manometer. Hence, this device measures pressure in the number of centimeters of water that are displaced (cm H2O) by the expiratory pressure. Individuals usually generate around 5 cm H2O of pressure to drive the vocal folds for phonation. Since it is unlikely the practicing speech-language pathologist will have access to a U-tube manometer, a somewhat antiquated device, a clinically applicable form of a manometer is a water glass manometer (Hixon et al., 1982). This is a device that can be assembled quickly and easily from a cup, paper clip, and straw. These are all objects easily found in any clinic or nurses’ station. The paper clip is used to secure the straw on the inside of the cup. Pour some water in the cup, and lower the straw until it is 5 cm below the water (Figure 3–9). If an individual can blow in the top of the straw and make bubbles come out of the bottom of the straw, then that individual has displaced 5 cm of H2O and therefore has the physical ability to generate enough expiratory pressure to drive the vocal folds for phonation.

Measuring Lung Volumes and Respiratory Capacities n

The amount of air in the lungs is divided into the volumes and capacities described earlier for measurement.

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Spirometry is the measurement of volumes and capacities of the respiratory system using a device called a spirometer.

n A

spirometer is a device used to measure most lung volumes and VC during respiration. When a clinician takes these measurements from a patient, the clinician is able to compare a patient’s measurements to normative data to determine if the patient’s respiratory capacity is normal or below normal.

FIGURE 3–9.  Hixon’s water glass manometer used to measure respiratory pressure.

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The most primitive form of a spirometer is known as a wet spirometer (Figure 3–10). A wet spirometer consists of one container sitting in a larger container of water. A tube that a person breathes into runs from the person’s mouth into the first container sitting within the water. When the person expires through the tube, the air moves into the first container, displacing the water within that container and causing it to rise. The degree of elevation of this rising container is used to generate measures of lung volumes and capacities.

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TV, IRV, and ERV can be measured directly. RV and total lung volume cannot be measured directly by spirometry because RV cannot be expired to be measured. RV and total lung volume must be calculated.

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Like the U-tube manometer, it is unlikely today’s speech-language pathologist will have access to a wet manometer. However, there are many small, handheld digital spirometry devices available to clinicians that can be used to take measurements such as VC. Many of these devices have mouthpieces with small rotary blades in them. When the patient expires or inspires, those blades turn, and the instrument measures the degree of movement of the blades; from that movement, lung volume capacities and rate are extrapolated.

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On a related note, a small plastic device known as an incentive spirometer is used by respiratory therapists to encourage deeper levels of expiratory and inspiratory volume during breathing.

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However, incentive spirometers do not provide hierarchical degrees of resistance to inspiration or expiration and therefore have limited application in therapy for strengthening muscles of

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FIGURE 3–10.  Wet spirometer.

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respiration. A resistive breathing device such as the one pictured in Figure 3–11 is needed to provide an increasing amount of resistance to inspiration and expiration, thereby exercising muscles to the point of strengthening them.

Therapy for Respiratory Weakness Weakness of the muscles of respiration that creates reduced respiratory support for speech and decreased communication is common on the caseload of the speech-language pathologist. Weakened muscles of respiration can have any number of etiologies but are very common in degenerative neuromuscular disorders such as amyotrophic lateral sclerosis, Parkinson disease, as well as more common conditions such as stroke or Alzheimer disease. Therapy for these individuals will vary according to their individual needs. However, therapy strategies tend to focus on increasing the strength of the muscles of the thorax and teaching compensatory strategies for the individual to learn to best communicate with reduced respiratory support for speech. An example of a therapy strategy to restore strength to respiratory muscles is the use of a resistive breathing device (Figure 3–11). These devices provide a greater degree of resistance to inspiration and/or expiration during use, thereby requiring greater muscular effort from the muscles of respiration. Used appropriately, these devices strengthen the muscles of respiration. During therapy sessions to target increasing inspiratory or expiratory capacity for speech, speech-language pathologists will prompt a patient to complete short bursts of repetitions of expiration or inspiration through one of these. An example of a compensatory strategy that may be used if increasing strength of respiratory muscles is not a viable option, is training the individual to best use what respiratory support they have for most effective verbal communication. This may include teaching the patient to remember to take as large an inspiration as possible prior to speaking to give them as much expiration as possible for their utterance. It may also include teaching the patient to be aware of how many words they are able to intelligibly produce with their reduced level of support and to stop speaking and take an inspiration to continue speaking once they have reached that limit.

FIGURE 3–11.  Resistive breathing device.

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➤ Process of Gas Exchange

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Despite the importance of the different patterns of respiration, mechanics of respiration, volumes, and capacities, none of that matters without the actual process of gas exchange, which is one of the primary life-giving functions of our bodies. The process of respiration is the body absorbing oxygen from inspired air and releasing carbon dioxide back into the air from the body. Oxygen is more abundant on earth than any other element. The air on earth that we breathe is mostly composed of nitrogen (78%) and oxygen (21%), with small amounts of other gases occurring as well. Upon inspiration, the oxygen content of air is 21%, but our bodies absorb approximately 5% of that volume of oxygen. Therefore, the concentration of oxygen in expired air is closer to 16%. Of this volume of oxygen that is absorbed by the body, the brain uses 20% of this oxygen to maintain function. That is more than any other organ in the body. The actual gas exchange of respiration happens at the molecular level within the millions of alveoli of the lungs (Figure 3–12). First, oxygen-rich air is drawn from the atmosphere into the lungs by the body. Oxygen passes from the alveolar air through the walls of the alveoli into the capillaries surrounding each alveolus, where oxygen molecules bind with hemoglobin, a protein in red blood cells. Once the oxygen binds with hemoglobin, the body uses the circulatory system for distribution of these oxygenated red blood cells to tissues and cells throughout the body for life-giving functions such as cellular respiration. Cellular respiration is the cells’ use of oxygen for metabolic purposes in the production of energy to power the cells of the body. One of the by-products of cellular respiration is carbon dioxide. This carbon dioxide by-product is released back into the circulatory system and is carried by red blood cells and plasma back toward the lungs. Once this carbon dioxide–rich blood is returned to the lungs, the carbon dioxide passes from within the blood-rich capillaries surrounding each alveolus through walls of the alveoli and into the alveolar air to be expelled from the body back into the atmosphere.

FIGURE 3–12.  Gas exchange at level of alveolus.

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Some important processes of respiration that need to be addressed in isolation from the previous explanation are ventilation, perfusion, and diffusion: n

The first process of respiration is known as ventilation, which is the movement of air into and out of the lungs (inspiration and expiration) (Figure 3–13). Also, it may be more specifically considered as the amount of oxygen reaching the alveoli. Appropriate levels of ventilation must be maintained in the body to ensure there is enough oxygen present in the alveoli to cross into the bloodstream for respiration.

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Perfusion is the process of the circulatory system delivering blood to the capillaries surrounding the alveoli (Figure 3–13). Appropriate levels of perfusion must be maintained in the body to ensure enough blood flow to the alveoli to maintain respiration. Maintaining appropriate perfusion is a function of the beating of the heart moving blood through the circulatory system. Therefore, decreased function of the heart eventually leads to a lack of appropriate perfusion at the alveoli.

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Diffusion is the process by which oxygen and carbon dioxide move passively through cell walls and across alveolar and capillary walls from areas of high concentration to areas of low concentration (Figure 3–13).

FIGURE 3–13.  Ventilation and perfusion.

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The level of oxygen present in the bloodstream is commonly referred to as blood oxygen level, oxygen saturation, or shorthand as O2 sat. Specifically, oxygen saturation is the measurement of the amount of oxygen-saturated hemoglobin compared to the total volume of hemoglobin in the body. Normal levels of oxygen saturation are usually in the 95% to 100% range but can be as low as 80%. Individuals with too low O2 saturation are described as being in a state of hypoxia (i.e., lacking appropriate levels of oxygen for appropriate function). A person may be in a state of hypoxia even though heart rate and respiratory rate may be normal. Hypoxic individuals often show cognitive slowness on tasks they would normally be successful at, or they may show outright cognitive or motor deficits that resolve when appropriate levels of oxygen are returned. The level of oxygen present in the blood is measured in two ways, a blood test or more commonly a device known as a pulse oximeter. A pulse oximeter is the tiny device that the nurse clips to the tip of your finger when checking your vital signs. This tiny device measures the amount of infrared light bounced off the oxygen-rich hemoglobin in the bloodstream to calculate O2 sat. Speech-language pathologists are often concerned with monitoring O2 sat when working with anyone with compromised respiratory function. This is especially true when the speechlanguage pathologist is targeting feeding or swallowing because to swallow, respiration must be interrupted, which can reduce O2 sat. Examples are: Speech-language pathologists that specialize in feeding medically fragile babies, such as in a Neonatal Intensive Care Unit, will closely monitor the O2 sat of premature babies who have decreased respiratory function while feeding them to ensure they are safely maintaining respiration while taking their meal. Also, while performing swallowing evaluations or therapy on adults with compromised respiration, such as COPD, who already may be hypoxic the speech-language pathologist must closely monitor O2 sat to keep the patient safe.

Current Events:  Black Lung Returns to Appalachia Many diseases are known to negatively affect the respiratory system. Of these, perhaps the most well known is black lung disease. Black lung disease is a fatal disease that is the result of coal miners inspiring dust in the air from their work extracting coal. The coal particulates build up in the lungs, creating inflammation and scarring of the lung tissue (Figure 3–14). This scarring creates the loss of alveoli and associated blood vessels, decreasing respiratory ability until the lungs can no longer supply the body with appropriate levels of oxygen. The United States saw rates of black lung disease increase among coal miners (Figure 3–15) until miners mobilized and went on strike in the late 1960s. At this time, around one third of coal miners who worked beneath the surface were affected by black lung disease (Atfield & Petsonk, 2007). These protests succeeded in the creation of higher safety standards for coal miners and set limits on the amount of dust workers could be exposed to. As a result, the United States saw decreasing levels of black lung disease through the 1990s to almost being extinguished.

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Blood Oxygen Level

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In 2005, evidence was published of rapidly growing clusters of black lung disease across Kentucky, Virginia, and West Virginia. This was an increase of 900% from the previous decade (Blackley, 2014). These new cases presented with a more severe, faster progressing, and damaging form of black lung disease created from miners being exposed to a combination of coal dust and increasing amounts of silica dust. Silica is a primary component of rock, and with depletion of large coal seams, miners must cut through more rock to reach what coal remains, generating greater amounts of silica dust. Also, increased mechanization of mining strategies creates finer-dust coal and silica particles that are able to pass deeper into the lungs and react more strongly with the tissue creating a more rapid and severe form of black lung disease. Many factors come into play in this resurgence of black lung, but critically, there was a failure on the part of the government and industry to update safety standards and procedures to keep miners safe as mining strategies changed and the type and amount of dust created changed.

FIGURE 3–14. Coal workers’ pneumoconiosis. Source: CDC Public Health Images Library/ Dr. Thomas Hooten. “This occupational health-related image depicts two lung tissue specimens extracted from two coal workers, each illustrating the effects of breathing in coal dust, leading to a condition known as, pneumoconiosis, or black lung disease. In pneumoconiosis, coal dust becomes imbedded in the lungs, causing them to harden, making breathing very difficult” (CDC, n.d.-a).

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FIGURE 3–15.  Indiana coal miner. Source: CDC Public Health Images Library/Barbara Jenkins, NIOSH; Bureau of Mines, Dept. of Interior. “Note how dusty the atmosphere was inside the closed confines of the mine shaft, and even more importantly, that neither man was wearing any filtered breathing devices. Mining coal, especially under circumstances like these close quarters, facilitated coal dust inhalation, thereby, predisposing miners to the long-term negative health effects of this profession including black lung disease, or coal-workers’ pneumoconiosis (CWP). Today, the federal government’s stringent regulations on the level of coal dust permissible in the air of a coalmine, and the requisite use of filtered breathing devices, has dramatically lowered the number of cases of black lung disease” (CDC, n.d.-b).

➤ Chapter Summary Respiration is the exchange of gases between an organism and the environment and is measured in cycles. It includes inspiration, the pulling of air into the lungs, and expiration, the pushing of air out of the lungs. A cycle of respiration consists of one inspiration and one expiration. Vegetative respiration is performed automatically to meet the body’s need for oxygen intake and carbon dioxide release. Vegetative respiration can be quiet respiration or forced respiration. Quiet respiration, also known as eupnea, is quiet inspiration and passive expiration. Quiet inspiration accounts for 40% of the respiratory cycle, while passive expiration accounts for 60% of this cycle.

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The respiratory center includes the areas of the brainstem responsible for regulating the rate and depth of vegetative breathing to meet the body’s need. During periods of increased physical activity, the respiratory center generates neural signals to increase the speed and volume of respiration for greater levels of oxygen intake. Forced respiration is the increase in speed and volume of respiration that engages muscles of inspiration and expiration to increase oxygen intake. Forced respiration, also known as hyperpnea, is forced inspiration and forced expiration. Children and infants have faster rates of quiet respiration than do adults. In part, this is due to the smaller lungs of children and infants, who require a faster exchange of air in the lungs to maintain appropriate oxygen levels than do adult lungs, which are capable of holding a greater volume of air. TV is the amount of air inspired and expired in a cycle of respiration. The TV and rate of respiration during quiet respiration change as the body grows and ages. Speech breathing is a forced respiration pattern that is used to volitionally commandeer the respiratory system to produce speech sounds. Inspiratory checking is the slow relaxing of muscles of inspiration after an inspiration, which allows the expiratory volume to be carefully controlled and utilized for speech. It is important in maintaining appropriate pressure beneath the vocal folds for phonation. The active force of respiration is muscular contraction. This is the contraction of muscles of inspiration and expiration used to increase or decrease volume of the lungs to inspire air into or expire air out of the lungs. Passive forces of respiration are gravity and tissue elasticity. Gravity affects respiration differently depending on the position of the body. Tissue elasticity is the degree to which the fibers of the body, once deformed, are subsequently able to passively retract to their original position. All the elastic body tissues that are stretched and distended during expansion of the thorax by the muscles of inspiration will retract themselves back to their resting position once the muscles of inspiration relax. The aerodynamic and muscular process of respiration involves the interaction and interplay of various pressures. Alveolar pressure is the air pressure within the alveoli of the lungs. Atmospheric pressure is the air pressure on the surface of the earth. More specifically, it is the amount of pressure created by gravity’s pull on the air on the surface of the earth. Intrapleural pressure is the pressure that exists within the pleural linkage. Intraoral pressure is the air pressure within the oral cavity. Subglottal pressure is the air pressure below the glottis, the space between the vocal folds. Molecules of air within a closed container exhibit Brownian motion: random, high-speed, and constant motion in which they are constantly colliding with each other and the walls of the container. It is the cumulative force of all these tiny individual collisions between the molecules of air within the container and the walls of the container that creates the amount of air pressure in the container. The more often air molecules are colliding with the interior of the container, the greater the air pressure is. The less often air molecules are colliding with the interior of the container, the less the air pressure is. Boyle’s law states that given a constant temperature, if the volume of a container is decreased, air pressure within that container increases, whereas if the volume of a container is increased, air pressure within the container decreases. Therefore, when the volume of the lungs increases, alveolar pressure decreases (inspiration). When volume of the lungs decreases, alveolar pressure increases (expiration). Quiet inspiration is primarily due to the contraction of the diaphragm. Inspiration will continue as long as the diaphragm continues to contract. Once the diaphragm reaches its maximal excursion point, pressure momentarily equalizes, and then expiration begins. Passive expiration

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begins as the diaphragm relaxes. The process of expiration continues until the thorax and lungs reach a position of rest. Forced respiration occurs when the body needs more oxygen quickly. Forced inspiration occurs when the muscles of inspiration contract to increase the volume of air inspired, as well as the speed to which it is inspired. Forced expiration occurs when the muscles of inspiration relax, and the muscles of expiration activate; it continues until the individual has reached the desired point of maximal expiration. The lung volumes are individual and separate divisions of the total amount of air that the lungs are capable of containing. The volume of air that is inspired and expired during a cycle of respiration is known as tidal volume (TV). TV is the amount of air pulled into the lungs during an inspiration. A tidal expiration is the amount of air expelled from the lungs during a expiration. Inspiratory reserve volume (IRV) is the maximal amount of air that can be inspired after a tidal inspiration. Expiratory reserve volume (ERV) is the maximal amount of air that can be expired after a tidal expiration. Residual volume (RV) is the amount of air that is always retained in the lungs and cannot be pushed out during expiration. Lung capacities are combinations of two or more lung volumes. Total lung capacity (TLC) is the amount of all air present in the lungs. Total lung capacity is all the lung volumes added together (TLC = TV + ERV + IRV + RV). Vital capacity (VC) is the amount of air you can expire after a maximal inspiration. VC is ERV plus TV plus IRV (VC = ERV + TV + IRV). The amount of air in the lungs after a quiet expiration is the functional residual capacity (FRC). FRC is RV plus ERV (FRC = RV + ERV). The total amount of air that can be inspired from the point of a tidal expiration is the inspiratory capacity (IC). IC is TV plus IRV volume (IC = TV + IRV). TV, RV, and VC increase with age and reach peak development between the ages of 20 and 25 years. After this age, there is an overall decline in respiratory function characterized by four primary changes: lung tissues become less elastic, the thorax becomes stiffer, muscles become weaker, and alveolar gas exchange becomes less efficient. Overall TLC declines slightly with normal age but not to a degree that impairs respiration. Respiration is typically measured by rate, pressure, and volume. Rate is measured in cycles of respiration per minute. Pressure is measured with a device called a manometer. The most basic manometer is a U-tube manometer. Spirometry is the measurement of volumes and capacities in the respiratory system; it uses a device called a spirometer. The actual gas exchange of respiration happens at the molecular level within the millions of alveoli of the lungs. Oxygen-rich air is drawn from the atmosphere into the lungs by the body to be absorbed into the circulatory system for transport by red blood cells. The body uses the circulatory system for distribution of oxygenated red blood cells to tissues and cells throughout the body for cellular respiration. Cellular respiration is the cells’ use of oxygen for metabolic purposes in the production of energy to power the cells of the body. A by-product of this process is carbon dioxide, which is released back into the circulatory system and is carried by red blood cells back to the lungs to be released into the alveolar air. Ventilation is the movement of air into and out of the lungs, specifically the amount of oxygen reaching the alveoli. Perfusion is the process of the circulatory system delivering blood to the capillaries surrounding the alveoli. Diffusion is the process by which oxygen and carbon dioxide move passively through cell walls and across alveolar and capillary walls from areas of high concentration to areas of low concentration.

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The level of oxygen present in the bloodstream is commonly referred to as blood oxygen level. Individuals with too little oxygen saturation are described as being in a state of hypoxia. This level of oxygen can be measured with a blood test or a device known as a pulse oximeter.

➤ References American Lung Association. (2019). Lung capacity and aging, 2019. https://www.lung.org/lunghealth-and-diseases/how-lungs-work/lung-capac​ ity-and-aging.html-2019 Atfield, M., & Petsonk, E. (2007) Advanced pneumoconiosis among working underground coal miners — Eastern Kentucky and Southwestern Virginia. Morbidity and Mortality Weekly Report, 56(6), 652–655. Blackley, D., Halldin, C. N., & Laney, A. S. (2014). Resurgence of a debilitating and entirely preventable respiratory disease among working coal miners. American Journal of Respiratory and Critical Care Medicine, 190(6), 708–709. https://doi.org/​ 10.1164/rccm.201407-1286le Centers for Disease Control and Prevention. (n.d.-a). Details: ID#: 2458. Coal workers pneumoconiosis. Public Health Image Library (PHIL). https:// phil​.cdc.gov/Details.aspx?pid=2458 Centers for Disease Control and Prevention. (n.d.-b). Details: ID#: 9544. Public Health Image Library (PHIL). https://phil.cdc.gov/Details.aspx?pid=​9544 Frank, N. R., Mead, J., & Ferris, B. G., Jr. (1957). The mechanical behavior of the lungs in healthy elderly persons. Journal of Clinical Investigation, 36(12), 1680–1687. https://doi.org/10.1172%2​ FJCI103569 Hixon, T. J. (1987). Respiratory function in speech. In T. J. Hixon (Ed.), Respiratory function in speech and song (pp. 1–54). Little, Brown, and Company. Hixon, T. J., Goldman, M. D., & Mead, J. (1973). Kinematics of the chest wall during speech pro-

duction: Volume displacements of the rib cage, abdomen, and lung. Journal of Speech and Hearing Research, 16, 78–115. https://doi.org/10.1044/ jshr.1601.78 Hixon, T. J., Hawley, J. L., & Wilson, K. J. (1982). An around-the-house device for the clinical determination of respiratory driving pressure: A note on making simple even simpler. Journal of Speech and Hearing Disorders, 47(7), 413–415. https:// doi.org/10.1044/jshd.4704.413 Hoit, J. D., & Hixon, T. J. (1987). Age and speech breathing. Journal of Speech and Hearing Research, 30, 351–360. https://doi.org/10.1044/jshr.3003​ .351 Hoit, J. D., Hixon, T. J., Altman, M. E., & Morgan, W. J. (1989). Speech breathing in women. Journal of Speech and Hearing Research, 32, 353–365. https://doi.org/10.1044/jshr.3202.353 Hoit, J. D., Hixon, T. J., Watson, P. J., & Morgan, W. J. (1990). Speech breathing in children and adolescents. Journal of Speech and Hearing Research, 33, 51–69. https://doi.org/10.1044/jshr.3301.51 Janssens, J., Pache, J., & Nicod, L. (1999). Physiological changes in respiratory function associated with aging. European Respiratory Journal, 13, 197– 205. https://doi.org/10.1034/j.1399-3003.1999​ .13a36.x Rahn, H., Otis, A., Chadwick, L., & Fenn, W. (1946). The pressure-volume diagram of the thorax and lung. American Journal of Physiology, 146(6), 161–178. https://doi.org/10.1152/aj​ plegacy.1946.146.2.161

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➤ Learning Objectives Upon completion of this chapter, students will be able to: n

Understand the anatomy of the larynx.

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Identify the cartilages, membranes, and ligaments of the larynx.

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Identify the muscles of the larynx.

➤ Introduction The human larynx evolved over time to produce sounds for communication. In various cultures, humans have demonstrated that they can produce sounds for speech with different pitches and types of phonation. To produce these sounds, humans need to have control over their vocal folds. The human larynx has biological functions that help with building up pressure for the vocal folds to vibrate, protecting the airway during swallowing, opening the vocal folds during phonation, and converting the air received from the lungs to acoustic energy via a process called phonation. Typically, for phonation to occur, the vocal folds in the larynx vibrate via a complex process that involves laryngeal muscles, cartilages, and soft tissue that work together to open and close the vocal folds. For voicing to occur, air from the lungs builds up at the subglottal level beneath the vocal folds. This subglottal air pressure blows the vocal folds apart causing a space between the vocal folds (glottis) (Figure 4–1). The decrease of pressure that results from transglottal airflow consequently sucks the vocal folds back together and results in one cycle of vocal fold vibration. After the vocal folds vibrate, the air is modified by the pharynx, mouth, lips, and tongue to produce sound. n

The vocal folds consist of two horizontally stretched mucous membranes that course anteriorly from the thyroid cartilage (Figure 4–2) and posteriorly from the arytenoid cartilages (Figures 4–3 and 4–4) (Nawka & Hosemann, 2005). 133

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FIGURE 4–1.  Glottis posterior view. Reproduced with permission from Anatomage.

FIGURE 4–2.  Thyroid cartilage posterior view. Reproduced with permission from Anatomage.

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FIGURE 4–4.  Glottis, thyroid cartilage, arytenoid cartilages posterior view. Reproduced with permission from Anatomage.

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FIGURE 4–3.  Arytenoid cartilage posterior view. Reproduced with permission from Anatomage.

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The vocal folds are covered by a thin superficial layer of squamous epithelium (Figure 4–5). Below the epithelium is the superficial lamina propria (Figure 4–5) that is composed of moist mucous membranes called mucosa. The superficial lamina propria and the squamous epithelium are connected by a thin layer — basement membrane (Gray et al., 1994) (Figure 4–5). The thyroarytenoid muscle is the deepest layer (Figure 4–5): n The

vocal fold epithelium provides structural stability to the vocal folds and protects the underlying connective tissue from sustaining injury.

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lamina propria is made up of three parts. These include the superficial, intermediate, and deep layers (Figure 4–5) and include elastin fibers that allow for stretching and collagenous fibers that provide strength. The second part — the intermediate layer — contains elastic fibers, and the third part — the deep layer — is collagenous. The intermediate and deep layers make up the vocal ligament that provides stiffness to the vocal folds (Figure 4–5). The mean thickness of the vocal ligament is between 1 and 2 mm.

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The deepest layer is the thyroarytenoid muscle (Figure 4–5), which is the body of the vocal folds. The thyroarytenoid muscle is divided into the thyromuscularis and vocalis muscles (Figure 4–6). The main purpose of the thyroarytenoid muscle is to reduce tension (relax) and shorten the vocal folds by drawing the arytenoid cartilages toward the thyroid cartilage resulting in a decrease in pitch.

A discussion of the larynx should include the hyoid bone (Figure 4–7). It is a U-shaped bone that is part of the axial skeleton and resides in the anterior of the neck. It is not directly attached to any other bone in the skeleton and is not part of the laryngeal framework; however, it supports the root of the tongue and suspends the larynx: n

The hyoid bone serves as a point of attachment for several extrinsic laryngeal muscles, floor of the mouth and tongue, pharynx, and epiglottis.

FIGURE 4–5.  Lamina propria.

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FIGURE 4–6.  Vocal ligament, thyroarytenoid muscle, vocalis muscle superior view. Reproduced with permission from Anatomage.

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The hyoid is made up of a body, two greater horns, and two lesser horns (Figure 4–8). The body is the main part of the bone and has an anterior convex surface and a posterior concave surface. The greater and lesser horns project from the side of the hyoid.

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The hyoid bone is involved in speech, swallowing, and breathing. During sleep, it functions to keep the upper airway open (Amatoury et al., 2014).

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FIGURE 4–7.  Hyoid bone and surrounding structures, anterior view. Reproduced with permission from Anatomage.

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FIGURE 4–8.  Hyoid bone — body, greater horns, and lesser horns, anterior view. Reproduced with permission from Anatomage.

➤ Larynx The larynx is often called the voice box and is essential for sound production. The larynx is located at the superior portion of the trachea: n

The laryngeal inlet or aditus is the opening that connects the pharynx and larynx. Located above the vocal folds is the laryngeal vestibule (entryway) that contains the false vocal folds (ventricular folds/vestibular folds) (Figure 4–9) that are covered by respiratory epithelium. The false folds contain some muscle fibers that are located in the lower half of the ventricular folds (posteriorly). Some ventricularis muscle is also present in the upper and lateral portion of these folds (Moon & Alipour, 2013). The false vocal folds, however, are not responsible for sound production.

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Between the vestibular folds and the true vocal folds is the laryngeal ventricle. n Until puberty, the larynges of males and females are similar; however, after puberty, the male larynx increases in size to about 23 mm. The female larynx is about 18 mm (Eckel et al., 1994). n

In adults, the larynx is located at the C3 to C6 vertebrae. However, the position of the larynx can vary slightly among individuals, depending on factors such as age, gender, and body size.

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Branches of cranial nerve (CN) X (vagus) (Figure 4–10) innervate the larynx bilaterally: n The internal branch of the superior laryngeal nerve (Figure 4–10) provides sensory innervation to the laryngeal vestibule and glottis. The cricothyroid muscle is innervated by the external branch of the superior laryngeal nerve (Figure 4–10). All other muscles of the larynx are provided motor innervation by the recurrent laryngeal nerve (Figure 4–10).

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The larynx has three primary functions: protecting the trachea from aspiration of food or liquids, breathing, and producing sound.

Cartilages of the Larynx The larynx is made up of six cartilages (three paired and three unpaired) (Figure 4–11, Table 4–1) as well as intrinsic and extrinsic muscles. 138

FIGURE 4–10.  Cranial nerve X — vagus nerve. Internal and external branch of the superior laryngeal nerve. Source: Figure 7.3b from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 265), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

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FIGURE 4–9.  Ventricular folds, superior view.

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FIGURE 4–11.  Cartilages of the larynx, lateral view. Reproduced with permission from Anatomage.

TABLE 4–1.

Cartilages of the Larynx

Paired

Unpaired

Arytenoid

Thyroid

Corniculate

Cricoid

Cuneiform

Epiglottis

Paired Cartilages The paired cartilages include the arytenoid, corniculate, and cuneiform cartilages (Figures 4–9 and 4–11). These cartilages are either hyaline or elastic: n The

arytenoids (Figure 4–11) are paired hyaline cartilages and are very important for speech production because they are attached to the vocal folds and allow for movement of the folds (Wei et al., 2015). n The arytenoids also impact the tension, relaxation, and position of the vocal folds. These triangular cartilages are located at the posterior-superior border of the cricoid cartilage (Figure 4–11). The base of each arytenoid cartilage is broad and concave to allow it to connect to the cricoid cartilage. The lateral surface is called the muscular process (Figure 4–6), and the anterior surface is called the vocal process (Figure 4–6). At the top of each arytenoid cartilage is a small conical structure called the corniculate cartilage (Figures 4–9 and 4–11): n The arytenoids have three surfaces. The anterolateral surface is rough and convex. Near the top of the cartilage is the colliculus (a rounded surface) from which the crista arcuata 140

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(a ridge) curves to join the vocal process. The bottom section of this peak has two depressions (fovea) — an upper triangular-shaped depression and a lower oblong-shaped depression that attaches to the vocalis muscle (Figure 4–6). The medial surface is covered by a mucous membrane. It is flat, narrow, and smooth and forms the lateral margin of the rima glottidis (glottis). The posterior surface is smooth, concave, and triangular. n The paired corniculate cartilages (cartilages of Santorini) are horn-shaped elastic cartilages that reside at the tip of each arytenoid cartilage. They are located posterior to the aryepiglottic folds (Figure 4–9). On occasion, the corniculate cartilages are joined with the arytenoid cartilages. The corniculate cartilages were named after the Italian anatomist Giovanni Santorini who performed anatomical dissections in the 1700s. Corniculate is derived from the Latin root cornu, which means a “hornlike projection.” n The paired cuneiform cartilages (Figures 4–9 and 4–11) sit on top of the arytenoids and move with them. They are wedge-shaped elastic cartilages that are located above and behind the corniculate cartilages and are covered by the aryepiglottic folds (Burdett & Mitchell, 2011). The cuneiform cartilages provide a solid structure to the vocal folds and support vocal fold motion.

Unpaired Cartilages The unpaired cartilages include the thyroid cartilage, the cricoid cartilage, and the epiglottis: thyroid cartilage is the largest cartilage in the larynx and is located in the front of the larynx — superior to the thyroid gland (Figure 4–12). It is more prominent in men (Sagiv et al., 2016). It is located between the C4 and C5 vertebrae. n The thyroid cartilage has two halves (thyroid laminae) that converge to form the laryngeal prominence (Adam’s apple) (Figure 4–13). Located above the laryngeal prominence is the superior thyroid notch (Figure 4–13), and at the bottom of the thyroid cartilage is the inferior thyroid notch (Figure 4–13). The two halves of the thyroid cartilage envelop the sides of the trachea. The posterior boundary of each half is connected to the cricoid cartilage from below

FIGURE 4–12.  Thyroid cartilage and thyroid gland, anterior view. Reproduced with permission from Anatomage.

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n The

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at the cricothyroid joint. The posterior portion of the thyroid cartilage has an upward and downward projection. The superior horn (cornu) (Figure 4–13) is the upper projection and is narrow and long. It is attached to the lateral thyrohyoid ligament (Figure 4–7). The inferior horn (Figure 4–13) is the lower projection and is thick and short and courses downward. It connects with the side of the cricoid cartilage. Another landmark on the thyroid cartilage is the oblique line (Figure 4–13), which marks the upper lateral borders of the thyroid gland. The thyrohyoid muscle and the inferior pharyngeal constrictor muscle originate on this line. The superior edge of the thyroid cartilage is connected to the hyoid bone by a ligament called the thyrohyoid membrane (Figure 4–14). The thyroid cartilage functions to protect the larynx. When the

FIGURE 4–13.  Thyroid cartilage. Reproduced with permission from Anatomage.

FIGURE 4–14. Thyrohyoid membrane, anterior view. Reproduced with permission from Anatomage.

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thyroid cartilage moves, it changes the tension of the vocal folds and results in variations in the pitch of the voice. n The

cricoid cartilage (Figures 4–15 and 4–16) is made up of hyaline cartilage. It is located at the C6 vertebra. Located on the superior surface of the cricoid cartilage is the posterior quadrate lamina (Figure 4–15). It connects with the arytenoid cartilages. The cricoid encircles the entire larynx and is an attachment site for the cricothyroid muscle, the lateral

FIGURE 4–16. Location of the cricoid cartilage, anterior view. Reproduced with permission from Anatomage.

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FIGURE 4–15.  Cricoid cartilage. Reproduced with permission from Anatomage.

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

cricoarytenoid muscle, the posterior cricoarytenoid muscle (Figure 4–17), as well as other ligaments and cartilages. It forms a ring of cartilage around the trachea and is often compared to a signet ring (Joshi et al., 2010). The cricoid cartilage is small enough to slip onto the little finger. It is located below the thyroid cartilage and is joined by the median cricothyroid ligament (Figure 4–18) as well as cricothyroid joints (Figure 4–15). Below the cricoid are C-shaped rings of cartilage that cover the trachea. The cricoid attaches to the first tracheal ring via the cricotracheal ligament. The anterior section of the cricoid is convex and narrow and has an arch that permits the vocal folds to pass over them. The lateral surfaces of the cricoid

FIGURE 4–17.  Cricothyroid muscle, lateral cricoarytenoid muscle, and the posterior cricoarytenoid muscle, superior view. Reproduced with permission from Anatomage.

FIGURE 4–18.  Cricothyroid ligament, anterior view. Reproduced with permission from Anatomage.

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articulate with the inferior horns of the thyroid cartilage at the cricothyroid joint that allows for a pivoting and rotational motion. The cricoid is involved in the opening and closing of the airway. With advanced age, the cricoid can get ossified and calcified. If the trachea is fractured, a cricodectomy can be performed. This procedure includes removing the cricoid cartilage partially or entirely to remove pressure on the trachea (Sone et al., 1996).

epiglottis (Figure 4–19) is an elastic cartilage that resembles a large spoon or leaf. It derives its name from being located above the glottis. The epiglottis is attached to the hyoid bone by the hyoepiglottic ligament (Figure 4–19). The lateral margins of the epiglottis are connected to the arytenoid cartilages via the aryepiglottic folds (Figures 4–9 and 4–19). The stem of the epiglottis is attached to the anterior of the thyroid cartilage via the thyroepiglottic ligament (Figure 4–19). The epiglottis sits at the entrance to the larynx, just posterior to the hyoid bone and the root of the tongue via the median and lateral glossoepiglottic ligaments that are covered by the epithelial glossoepiglottic folds. At this location is the valleculae — space (sinus) (Figure 4–20) that speech-language pathologists observe during modified barium swallow studies. These studies are used to determine whether there is premature spillage or residue (food or liquid) in cavities like the valleculae in patients who have swallowing difficulties (Matsuo & Palmer, 2008). The pyriform sinuses (Figure 4–20) are also located adjacent to the valleculae. These are small spaces that are located between the mucus lining of the thyroid cartilage and the aryepiglottic folds. These two landmarks (valleculae and pyriform sinuses) make up the pharyngeal recesses. The epiglottis serves as a valve that points upward and remains open during breathing; however, it closes during swallowing as the hyoid bone elevates to move the larynx upward. This action prevents aspiration (when food or liquid goes below the level of the vocal folds) as the food is directed toward the esophagus instead of the trachea. Fibers from CN IX (glossopharyngeal nerve) enter the upper epiglottis resulting in the afferent limb of the gag reflex. Fibers from the superior laryngeal branch of CN X (vagus nerve) enter the lower epiglottis

FIGURE 4–19.  Epiglottis, posterior view. Reproduced with permission from Anatomage.

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n The

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FIGURE 4–20.  Valleculae, anterior view.

resulting in the efferent limb of the cough reflex (to try and remove any food or liquid that may be trapped in the trachea). Interestingly, the epiglottis has taste buds (Jowett & Shrestha, 1998). These include five aspects of taste including sweet, sour, savory, salty, and bitter. Epiglottitis is a medical condition that may result in death if not immediately treated. When the epiglottis gets infected, it can block the trachea. Causes of epiglottitis can include viruses, bacteria, fungi, or drinking very hot liquids or foods.

Membranes and Ligaments The larynx includes either intrinsic or extrinsic laryngeal membranes. Several membranes and ligaments connect the laryngeal cartilages with other structures outside the larynx.

Extrinsic Laryngeal Membranes and Ligaments These are called extrinsic laryngeal membranes and ligaments and include the hyoepiglottic ligament, thyrohyoid ligament, cricotracheal membrane, and thyrohyoid membrane:

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n The

hyoepiglottic ligament connects the anterior part of the epiglottis to the upper body of the hyoid. n The paired lateral thyrohyoid ligament (Figure 4–7) forms the posterior border of the thyrohyoid membrane and courses through the tip of the superior cornu of the thyroid cartilage and the greater cornu of the hyoid bone. Patients who often complain of a unilateral pain in the neck and odynophagia (pain when swallowing) are diagnosed with lateral thyrohyoid ligament syndrome because of overuse or inflammation (Singha et al., 2014). The hyoepiglottic ligament is relevant when performing direct laryngoscopy. The laryngoscope blade tip is placed in the vallecular and moved forward. This causes the ligament to move the epiglottis anteriorly so that the glottis can be visualized. With advanced age, the hyoepiglottic ligament weakens and may result in aspiration, acquired laryngomalacia, and obstructive sleep apnea syndrome (Sawatsubashi et al., 2010). n The

cricotracheal membrane (Figure 4–21) connects the lower portion of the cricoid cartilage with the first ring of the trachea. n The thyrohyoid membrane (Figure 4–22) suspends the larynx and is located between the hyoid bone and the superior border of the thyroid cartilage. Medially, it is referred to as the middle thyrohyoid ligament (Figure 4–22). Posteriorly, it is called the lateral thyrohyoid ligament. The triticeal (the size of a grain of wheat) cartilage, a tiny nodule, is often found in this ligament (Wilson et al., 2017).

Intrinsic Laryngeal Membranes

FIGURE 4–21.  Cricotracheal membrane, anterior view. Reproduced with permission from Anatomage.

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Intrinsic laryngeal membranes mostly originate from the elastic membrane — a broad sheet of connective tissue that lines most of the interior of the larynx. The lower part of this membrane is called

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 4–22.  Thyrohyoid membrane, anterior view. Reproduced with permission from Anatomage.

the conus elasticus, and the upper part is called the quadrangular membrane. These membranes have attachments that lie within the cartilaginous larynx: n

Aryepiglottic folds (Figures 4–9 and 4–19) are paired structures that form the upper portion of the quadrangular membrane. They extend between the arytenoid cartilage and the lateral margin of the epiglottis on either side and form the lateral borders of the laryngeal inlet (Reidenbach, 1998). Within the aryepiglottic folds are the cuneiform cartilages (Figures 4–9 and 4–11). The pyriform sinus is located between the aryepiglottic folds and the thyroid cartilages. When people have swallowing difficulties, food may be lodged in the pyriform sinuses and may result in difficulty swallowing.

n The

conus elasticus, a yellow, elastic funnel-like cavity that resides below the vocal folds is integral to the makeup of the vibrating part of the vocal folds (Reidenbach, 1996). It is the lateral portion of the cricothyroid ligament (Figure 4–22) and is an important structure because it connects the arytenoid, thyroid, and cricoid cartilages. The conus elasticus courses from the superior border of the lamina arch of the cricoid cartilage to the upper edge of the true vocal folds. It is further divided into an anterior part — middle cricothyroid ligament (Figure 4–22) and lateral cricothyroid membranes: n

n

n

The medial cricothyroid ligament is yellow, elastic tissue that is strong and thick and connects the front parts of the contiguous margins of the thyroid and cricoid cartilages. The lateral cricothyroid membranes are thinner than the anterior portion and are located close to the mucous membrane of the larynx. They course from the superior border of the cricoid cartilage to the inferior portion of the vocal ligaments (located in the body of a vocal fold and form the medial part of the vocal fold).

The quadrangular membranes are made up of collagen and elastic fibers and contain the cuneiform cartilages (Young et al., 2014). The membrane courses from the lateral portions of the epiglottis and arytenoid on each side and attaches to the corniculate cartilages. The 148

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quadrangular membranes course inferiorly to the ventricular ligaments that attach to the ventricular folds or “false vocal folds.” The vestibular fold is the free inferior edge of the quadrangular membrane, and the superior portion is located in the aryepiglottic fold.

Muscles of the Larynx There are intrinsic (Figure 4–23, Table 4–2) and extrinsic muscles of the larynx. The intrinsic muscles are responsible for opening and closing of the vocal folds and include the following muscles that are housed within the larynx: n

transverse and oblique arytenoids (interarytenoid) n cricothyroid n lateral cricoarytenoid n thyroarytenoid n posterior cricoarytenoid

n

suprahyoid (above the hyoid bone) n digastric n geniohyoid n mylohyoid n stylohyoid

n

infrahyoid (below the hyoid bone) n omohyoid n thyrohyoid n sternohyoid n sternothyroid

FIGURE 4–23.  Intrinsic laryngeal muscles, posterior view. Reproduced with permission from Anatomage.

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The main purpose of the extrinsic muscles is to support the larynx in a fixed position (Thiagarajan, 2015). These muscles include the following muscles and have one attachment outside the larynx and for the most part have one attachment on the hyoid bone:

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Intrinsic

TABLE 4–2.

Intrinsic Laryngeal Muscles

Muscle

Origin

Insertion

Innervation

Function

Interarytenoid (transverse and oblique)

Posterior surface and lateral edge of one arytenoid cartilage

Corresponding part of the opposite arytenoid cartilage

Recurrent laryngeal nerve

Closes the posterior portion of the rima glottidis (opening of the glottis) and adducts the arytenoid cartilages resulting in narrowing of the laryngeal inlet

Cricothyroid

Anterolateral part of the cricoid cartilage

Inferior horn and inferior margin of the thyroid cartilage

External branch of the superior laryngeal nerve

Tenses and stretches the vocal ligaments, which results in more forceful speech

Lateral cricoarytenoid

The arch of the cricoid cartilage

Muscular process of the arytenoid cartilage

Recurrent laryngeal branch of the vagus nerve (CN X)

Narrows the rima glottidis resulting in modulation of the volume of speech; the major adductor of the vocal folds

Thyroarytenoid

Inferiorposterior angle of the thyroid cartilage

Anterolateral portion of the arytenoid cartilage

Recurrent laryngeal nerve

Relaxes the vocal ligament, which results in a quieter voice and lower pitch

Posterior cricoarytenoid

Posterior surface of the cricoid cartilage

Muscular process of the arytenoid cartilage

Recurrent laryngeal nerve

Only abductors of the vocal folds resulting in widening of the rima glottidis

Intrinsic Muscles of the Larynx Interarytenoid (Figures 4–24 and 4–25): n

Origin n

n

Insertion n

n

Corresponding part of the opposite arytenoid cartilage

Innervation n

n

Posterior surface and lateral edge of one arytenoid cartilage

CN X (vagus nerve). The recurrent laryngeal nerve (RLN) branches off from the vagus nerve. The terminal branch of RLN is the inferior laryngeal nerve that innervates the arytenoid.

Function n

Closes the posterior portion of the rima glottidis (opening of the glottis)

n

Adducts the arytenoid cartilages resulting in narrowing of the laryngeal inlet 150

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FIGURE 4–24.  Oblique arytenoid, posterior view. Reproduced with permission from Anatomage.

FIGURE 4–25.  Transverse arytenoid, posterior view. Reproduced with permission from Anatomage.

Cricothyroid (Figure 4–26): Origin n

n

Insertion n

n

Inferior horn and inferior margin of the thyroid cartilage

Innervation n

n

Anterolateral part of the cricoid cartilage

CN X (vagus nerve). External branch of the superior laryngeal nerve is a branch of the vagus nerve.

Function n

Tenses the vocal ligaments, which results in vocal fold adduction; responsible for pitch changes

n

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n

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The cricothyroid muscle is the only laryngeal muscle that is innervated by the superior laryngeal branch of the vagus nerve. Lateral Cricoarytenoid (Figure 4–27): n

Origin n

n

Insertion n

n

The arch of the cricoid cartilage Muscular process of the arytenoid cartilage

Innervation n

CN X (vagus nerve); recurrent laryngeal branch

FIGURE 4–26. Cricothyroid muscle, posterior view. Reproduced with permission from Anatomage.

FIGURE 4–27.  Lateral cricoarytenoid muscle, posterior view. Reproduced with permission from Anatomage.

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Function n

Narrows the rima glottidis resulting in the modulation of the volume of speech

n

Major adductor of the vocal folds

Thyroarytenoid muscle (Figure 4–28): n

Origin n

n

Insertion n

n

Anterolateral portion of the arytenoid cartilage

Innervation n

n

Inferior-posterior angle of the thyroid cartilage

CN X (vagus nerve). The RLNs branch off from the vagus nerve. The terminal branch of the RLN is the inferior laryngeal nerve that innervates the thyroarytenoid.

Function n

Reduce tension (relax) and shorten the vocal folds

Posterior Cricoarytenoid (Figure 4–29): Origin n

n

Insertion n

n

Muscular process of the arytenoid cartilage

Innervation n

n

Posterior surface of the cricoid cartilage

CN X (vagus nerve). The RLNs branch off from the vagus nerve. The terminal branch of the RLN is the inferior laryngeal nerve that innervates the posterior cricoarytenoid.

Function n

Only abductors of the vocal folds

n

Widening of the rima glottidis

FIGURE 4–28.  Thyroarytenoid muscle, posterior view. Reproduced with permission from Anatomage.

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n

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FIGURE 4–29.  Posterior cricoarytenoid muscle, posterior view. Reproduced with permission from Anatomage.

If the posterior cricoarytenoid muscles are paralyzed, it may result in asphyxiation because they are the only muscles of the larynx that open the true vocal folds. The intrinsic muscles are further divided into phonatory (adductors and tensors) and respiratory (the posterior cricoarytenoid) muscles: n

Phonatory (these muscles are involved in voice production): n

Adductors n The interarytenoid is a single muscle. It arises from the lateral surface and posterior border of one arytenoid cartilage and inserts into the opposite arytenoid cartilage. The interarytenoid muscle is divided into the transverse and oblique arytenoid muscles that are also known as the interarytenoid muscles (Choi et al., 1995). n The transverse arytenoid muscle originates from the posterior surface and muscular process of the arytenoid cartilage and inserts into the opposite cartilage. It is innervated by the vagus nerve (CN X) and adducts the arytenoid cartilages. When contracted, it pulls the arytenoids together and results in adducted vocal folds (Choi et al., 1995). n The oblique arytenoid muscles are superficial to the transverse arytenoid muscle. The oblique arytenoid muscles cross each other and course from the base of one cartilage to the tip of the opposite cartilage by crossing over each other like the letter X. It narrows the laryngeal inlet by contracting the distance between the arytenoid cartilages. It is innervated by the vagus nerve (CN X). Along with the aryepiglottic muscle, the transverse arytenoid, and the thyroarytenoid, it acts like a sphincter to close the larynx during coughing and swallowing (Choi et al., 1995). n The lateral cricoarytenoid muscles course from the cricoid cartilage to the muscular process of the arytenoid cartilage. These muscles adduct and rotate the arytenoid cartilages from the inside and increase medial compression (Yin & Zhang, 2014). They

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serve to protect the airway. These muscles also narrow the rima glottidis resulting in the modulation of the volume of speech and they act antagonistically to the posterior cricoarytenoid muscles. n The thyroarytenoid muscles are thin and broad muscles that form the main body of the vocal folds. They arise from the bottom half of the thyroid cartilage and the middle cricothyroid ligament and insert into the anterior and base of the arytenoid cartilage. Located within the thyroarytenoid muscles are deeper triangular band of fibers that insert into the vocal process of the arytenoid cartilage. The thyroarytenoid muscles function to shorten and relax the vocal folds as well as lower pitch (Yin & Zhang, 2014). n The cricothyroid muscle (lengthens and tenses the vocal folds) has two separate muscle bellies that are located on the external surface of the laryngeal cartilages. The pars obliqua courses obliquely from the superior arch of the cricoid cartilage and inserts into the inferior cornu. The pars recta is the more vertical portion of the muscle belly. It arises laterally from the superior edge of the cricoid cartilage and inserts into the inferior border of the thyroid cartilage. When this muscle contracts, the cricoarytenoid joints and the posterior cricoid lamina lengthen, tighten, and thin the vocal folds. The cricothyroid space is narrowed anteriorly, resulting in vocal fold adduction (Yin & Zhang, 2014). n

Respiratory muscles (permit the vocal folds to move during breathing): n

The posterior cricoarytenoid muscle (abduct the vocal folds; rotate the arytenoid cartilages from the outside) is the only muscle that is involved in opening the vocal folds for normal breathing (Chhetri et al., 2014). If there is injury to these muscles or bilateral damage to the RLN that supplies these muscles, it may result in an inability to abduct the vocal folds with a resultant risk of having breathing difficulties.

Extrinsic Muscles of the Larynx

FIGURE 4–30.  Extrinsic laryngeal muscles (suprahyoid), anterior view. Reproduced with permission from Anatomage.

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Extrinsic Muscles of the Larynx:  Suprahyoid (Figure 4–30, Table 4–3)

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Extrinsic

TABLE 4–3.

Extrinsic Laryngeal Muscles (Suprahyoid)

Muscle

Origin

Insertion

Innervation

Function

Digastric (Suprahyoid)

Anterior belly originates from the digastric fossa of the mandible; posterior belly originates from the mastoid process of the temporal bone

Two bellies connected by an intermediate tendon that is attached to the hyoid bone by a fibrous sling

Anterior belly is innervated by the inferior alveolar nerve that is a branch of the mandibular nerve of the trigeminal nerve (CN V); posterior belly is innervated by the digastric branch of CN VII (facial nerve)

Elevates the larynx; elevates the hyoid bone and depresses the mandible

Geniohyoid (suprahyoid)

Inferior mental spine of the mandible

Courses inferiorly and posteriorly and attaches to the hyoid bone

Fibers of the first cervical nerve (C I) roots that run within the hypoglossal nerve (CN XII)

Elevates the larynx; elevates the hyoid bone and depresses the mandible

Mylohyoid (suprahyoid)

Mylohyoid line of the mandible

Attaches onto the hyoid bone

Inferior alveolar nerve, a branch of the mandibular nerve (derived from CN V— the trigeminal nerve)

Elevates the larynx; elevates the floor of the mouth, tongue, and the hyoid bone

Stylohyoid (suprahyoid)

Styloid process of the temporal bone

Lateral part of the hyoid bone

Stylohyoid branch of CN VII — facial nerve arises proximally to the parotid gland

Elevates the larynx; initiates a swallow by pulling the hyoid bone posteriorly and superiorly

Digastric (Figure 4–31): n

n

Origin n

Anterior belly originates from the digastric fossa of the mandible

n

Posterior belly originates from the mastoid process of the temporal bone

Insertion n

n

The two bellies are connected by an intermediate tendon that is attached to the hyoid bone by a fibrous sling.

Innervation n

n

CN V (trigeminal nerve) — Anterior belly is innervated by the inferior alveolar nerve, which is a branch of the mandibular nerve of CN V. CN VII (facial nerve) — Posterior belly is innervated by the digastric branch of CN VII.

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Function n

Elevates the larynx

n

Elevates the hyoid bone

n

Depresses the mandible

Geniohyoid (Figure 4–32): Origin n

Inferior mental spine of the mandible

FIGURE 4–31.  Digastric muscle, lateral view. Reproduced with permission from Anatomage.

FIGURE 4–32.  Geniohyoid muscle, lateral view. Reproduced with permission from Anatomage.

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n

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

n

Insertion n Courses inferiorly and posteriorly and attaches to the hyoid bone

n

Innervation n Fibers of the first cervical nerve (C1) roots that run within the hypoglossal nerve (CN XII)

n

Function n Elevates the larynx n Elevates the hyoid bone n Depresses the mandible

Mylohyoid (Figure 4–33): n

Origin n Mylohyoid line of the mandible

n

Insertion n Attaches to the hyoid bone

n

Innervation n Inferior alveolar nerve, a branch of the mandibular nerve (derived from CN V)

n

Function n Elevates the larynx n Elevates the floor of the mouth n Elevates the tongue n Elevates the hyoid bone

Stylohyoid (Figure 4–34): n

Origin n Styloid process of the temporal bone

FIGURE 4–33.  Mylohyoid muscle, lateral view. Reproduced with permission from Anatomage.

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FIGURE 4–34.  Stylohyoid muscle, lateral view. Reproduced with permission from Anatomage.

n

Insertion n

n

Innervation n

n

Lateral part of the hyoid bone CN VII (facial nerve) — Stylohyoid branch of CN VII; facial nerve arises proximally to the parotid gland

Function n

Elevates the larynx

n

Initiates a swallow by pulling the hyoid bone posteriorly and superiorly

FIGURE 4–35.  Extrinsic laryngeal muscles (infrahyoid), lateral view. Reproduced with permission from Anatomage.

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Extrinsic Muscles of the Larynx: Infrahyoid (Figure 4–35, Table 4–4)

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

TABLE 4–4.

Extrinsic Laryngeal Muscles (Infrahyoid)

Muscle

Origin

Insertion

Innervation

Function

Omohyoid (infrahyoid)

Inferior belly of the omohyoid arises from the scapula (shoulder blade)

Superior belly via an intermediate tendon and attaches to the hyoid bone

Branch of the cervical plexus, the ansa cervicalis. The inferior belly is innervated by cervical nerves (C1, C2, C3).

Depresses the hyoid bone and larynx; draws the larynx down during phonation; active during the end phase of swallowing

Extrinsic

Courses superomedially and passes behind the sternocleido­ mastoid muscle Thyrohyoid (infrahyoid)

Oblique line on the lamina of the thyroid cartilage

Lower border of the greater cornu of the hyoid bone

Anterior ramus of C1 (cervical nerve), carried within the hypoglossal nerve (CN XII).

Depresses the hyoid; elevates the thyroid gland

Sternohyoid (infrahyoid)

Sternum and sternoclavicular joint

Hyoid bone

Anterior rami of cervical nerves C1, C2, C3, carried by a branch of the ansa cervicalis

Depresses the hyoid and larynx

Sternothyroid (infrahyoid)

Posterior surface of the manubrium of the sternum

Oblique line on the lamina of the thyroid cartilage

Anterior rami of cervical nerves C1, C2, C3, carried by a branch of the ansa cervicalis

Depresses the thyroid cartilage and the larynx

Omohyoid (Figure 4–36): n

n

Origin n

Inferior belly of the omohyoid arises from the scapula (shoulder blade)

n

Courses superomedially and passes behind the sternocleidomastoid muscle

Insertion n

n

n

Superior belly via an intermediate tendon and attaches to the hyoid bone

Innervation n

Branch of the cervical plexus, the ansa cervicalis

n

The inferior belly is innervated by cervical nerves (C1, C2, C3).

Function n

Depresses the hyoid bone

n

Depresses the larynx during phonation

n

Active during the end phase of swallowing 160

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FIGURE 4–36.  Omohyoid muscle, anterior view. Reproduced with permission from Anatomage.

To check the functioning of the omohyoid muscle, place the fingers in the front and middle of the neck and swallow. During swallowing, the neck should move up and down. The neck moves down because the omohyoid muscles are active. Thyrohyoid (Figure 4–37): Origin n Oblique line on the lamina of the thyroid cartilage

n

Insertion n Lower border of the greater cornu of the hyoid bone

n

Innervation n Anterior ramus of cervical nerve C1, carried within the hypoglossal nerve (CN XII)

n

Function n Depresses the hyoid n Elevates the thyroid gland

Anatomy of Phonation

n

Sternohyoid (Figure 4–38): n

Origin n Sternum and sternoclavicular joint

n

Insertion n Hyoid bone 161

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FIGURE 4–37.  Thyrohyoid muscle, ante­ rior view. Reproduced with permission from Anatomage.

n

Innervation n

n

FIGURE 4–38.  Sternohyoid muscle, ante­ rior view. Reproduced with permission from Anatomage.

Anterior rami of cervical nerves C1, C2, C3, carried by a branch of the ansa cervicalis

Function n

Depresses the hyoid

n

Depresses the larynx

Sternothyroid (Figure 4–39): n

Origin n

n

Insertion n

n

Oblique line on the lamina of the thyroid cartilage

Innervation n

n

Posterior surface of the manubrium of the sternum

Anterior rami of cervical nerves C1, C2, C3, carried by a branch of the ansa cervicalis

Function n

Depresses the thyroid cartilage

n

Depresses the larynx The sternothyroid muscle is important for swallowing and chewing. Since this muscle helps with depressing the thyroid cartilage, it may affect volume, pitch, and vocal range. If there is damage to this muscle, a person may have trouble eating or talking.

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FIGURE 4–39.  Sternothyroid muscle, anterior view. Reproduced with permission from Anatomage.

The human larynx mainly functions to convert the air received from the lungs into acoustic energy via a process called phonation. For voicing to occur, air from the lungs passes through the glottis. The vocal folds consist of two horizontally stretched mucous membranes. The vocal folds are covered by a superficial layer of squamous epithelium that provides the shape of the vocal folds. A discussion of the larynx should include the hyoid bone. It is a U-shaped bone that is part of the axial skeleton and resides in the anterior of the neck. It is not directly attached to any other bone in the skeleton and is not part of the laryngeal framework. The larynx is often called the voice box and is essential for sound production. The larynx is located at the superior portion of the trachea. The larynx is made up of six cartilages: three paired — arytenoid, corniculate, and cuneiform cartilages; and three unpaired — thyroid, cricoid, and epiglottis as well as intrinsic and extrinsic muscles. The larynx includes either intrinsic or extrinsic laryngeal membranes. Several membranes and ligaments connect the laryngeal cartilages with other structures outside the larynx. These are called extrinsic laryngeal membranes and ligaments and include the hyoepiglottic ligament, the paired lateral thyrohyoid ligament, the cricotracheal membrane, and the thyrohyoid membrane. Intrinsic laryngeal membranes mostly originate from the elastic membrane — a broad sheet of connective tissue that lines most of the interior of the larynx. The lower part of this membrane is called the conus elasticus, and the upper part is called the quadrangular membrane. These membranes have attachments that lie within the cartilaginous larynx and include the aryepiglottic folds, the conus elasticus, and the quadrangular membranes.

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➤ Chapter Summary

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

There are also intrinsic and extrinsic muscles of the larynx. The intrinsic muscles include the arytenoid, cricothyroid, lateral cricoarytenoid, thyroarytenoid, and the posterior cricoarytenoid muscles. The intrinsic muscles are housed within the larynx. The extrinsic muscles include suprahyoid (digastric, geniohyoid, mylohyoid, stylohyoid) and infrahyoid (omohyoid, thyrohyoid, sternohyoid, sternothyroid) muscles. They have one attachment outside the larynx and for the most part have one attachment on the hyoid bone. The main purpose of these muscles is to support the larynx in a fixed position.

➤ References Amatoury, J., Kairaitis, K., Wheatley, J. R., Bilston, L. E., & Amis, T. C. (2014). Peripharyngeal tissue deformation and stress distributions in response to caudal tracheal displacement: Pivotal influence of the hyoid bone? Journal of Applied Physiology, 116(7), 746–756. https://doi.org/10.1152/ japplphysiol.01245.2013 Burdett, E., & Mitchell, V. (2011). Anatomy of the larynx, trachea, and bronchi. Anaesthesia and Intensive Care Medicine, 12(8), 335–339. https:// doi.org/10.1016/j.mpaic.2008.06.005 Chhetri, D. K., Neubauer, J., & Sofer, E., (2014). Posterior cricoarytenoid muscle dynamics in canines and humans. Laryngoscope, 124(10), 2363–2367. https://doi.org/10.1002%2Flary.24742 Choi, H. S., Ye, M., & Berke, G. S. (1995). Function of the interarytenoid (IA) muscle in phonation: In vivo laryngeal model. Yonsei Medical Journal, 36(1), 58–67. https://doi.org/10.3349/ ymj.1995.36.1.58 Eckel, H. E., Sittel, C., Zorowka, P., & Jerke, A. (1994). Dimensions of the laryngeal framework in adults. Surgical and Radiological Anatomy, 16(1), 31–36. https://doi.org/10.1007/bf01627918 Gray, S. D., Pignatari, S. S., & Harding, P. (1994). Morphologic ultrastructure of anchoring fibers in normal vocal fold basement membrane zone. Journal of Voice, 8(1), 48–52. https://doi.org/10.1016/ s0892-1997(05)80318-2 Joshi, M., Joshi, S., & Joshi, S. (2011). Morphometric study of cricoid cartilages in Western India. Australasian Medical Journal, 4(10), 542–547. https://doi.org/ 10.4066/AMJ.2011.816 Jowett, A., & Shrestha, R. (1998). Mucosa and taste buds of the human epiglottis. Journal of Anatomy,

193(4), 617–618. https://doi.org/10.1046%2Fj​ .1469-7580.1998.19340617.x Matsuo, K., & Palmer, J. B. (2008). Anatomy and physiology of feeding and swallowing — Normal and abnormal. Physical Medicine and Rehabilitation Clinics of North America, 19(4), 691–707. https://doi.org/10.1016%2Fj.pmr.2008.06.001 Moon, J., & Alipour, F. (2013). Muscular anatomy of the human ventricular folds. Annals of Otology, Rhinology, and Laryngology, 122(9), 561–567. https:// doi.org/10.1177%2F000348941312200905 Nawka, T., & Hosemann, W. (2005). Surgical procedures for voice restoration. GMS Current Topics in Otorhinolaryngology Head and Neck Surgery, 4, 14. Reidenbach, M. M. (1996). The attachments of the conus elasticus to the laryngeal skeleton: Physiologic and clinical implications. Clinical Anatomy, 9(6), 363–370. https://doi.org/10.1002/(sici)​ 1098-2353(1996)9:6%3C363::aid-ca1%3E3​ .0.co;2-c Reidenbach, M. M. (1998). Aryepiglottic fold: Normal topography and clinical implications. Clinical Anatomy, 11(4), 223–235. https://doi.org/10.10​ 02/(sici)1098-2353(1998)11:4%3C223::aidca1%3E3.0.co;2-s Sagiv, D., Mansour, E. A., Nakache, G., Wolf, M., & Primov-Fever, A. (2016). Novel anatomic characteristics of the laryngeal framework: A computed tomography evaluation. Otolaryngology and Head and Neck Surgery, 154(4). 674–678. https://doi​ .org/10.1177/0194599815627781 Sawatsubashi, M., Umezaki, T., Kusano, K., Tokunaga, O., Oda, M., & Komune S. (2010). Agerelated changes in the hyoepiglottic ligament: Functional implications based on histopathologic

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study. American Journal of Otolaryngology, 31(6), cer. Oncology Letters, 10(2), 637–640. https://doi​ 448–452. https://doi.org/10.1016/j.amjoto​.2009​ .org/10.3892/ol.2015.3362 .08.003 Wilson, I., Stevens, J., Gnananandan, J., NabeebacSingha, P., Grindler, D. J., & Haughey, B. H. (2014). cus, A., Sandison, A., & Hunter, A. (2017). TriA pain in the neck: Lateral thyrohyoid ligament ticeal cartilage: The forgotten cartilage. Surgical syndrome. Laryngoscope, 124(1), 116–118. https://​ and Radiological Anatomy, 39(10), 1135–1141. doi.org/10.1002/lary.24419 https://doi.org/10.1007%2Fs00276-017-1841-z Sone, M., Nakashima, T., & Yanagita, N. (1996). Yin, J., & Zhang, Z. (2014). Interaction between the Laryngotracheal separation under local anaesthyroarytenoid and lateral cricoarytenoid muscles thesia for intractable salivary aspiration: Criin the control of vocal fold adduction and Eigen coidectomy with fibrin glue support. Journal of frequencies. Journal of Biomechanical Engineering, Laryngology and Otology, 110(1), 72–74. https:// 136(11), 1110061–1110061. https://doi.org/10​ doi.org/​10.1017/s0022215100132761 .1115/1.4028428 Thiagarajan, B. (2015). Anatomy of the larynx. Oto- Young, N., Abdelmessih, M. W., & Sasaki, C. (2014). laryngology Online Journal, 5(1.5), 1–12. Hajek revisited: A histological examination of Wei, B., Shen, H., & Xie, H. (2015). Laryngeal the quadrangular membrane. Annals of Otology, function reconstruction with hyoid osteomuscuRhinology, and Laryngology, 123(11), 765–768. lar flap in partial laryngectomy for laryngeal canhttps://doi.org/10.1177/0003489414538398

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➤ Learning Objectives Upon completion of this chapter, students will be able to: n

Describe and understand the biological functions of the larynx that do not relate to phonation.

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Define prominent theories of phonation: the myoelasticaerodynamic theory, body-cover theory, and nonlinear source-filter coupling theory.

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Learn the acoustic aspects of phonation, including but not limited to pitch, fundamental frequency, and harmonics.

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Learn the linguistic aspects of phonation, such as prosody, intonation, and stress.

➤ Nonspeech (Biological) Functions Although the larynx is mostly known for its role as the “voice box,” it serves four other main purposes within the body, known as the biological functions of the larynx. These include n breathing n

abdominal fixation

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protection during the swallow reflex

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throat clearing and coughing

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Breathing The larynx is considered part of the lower respiratory system and is involved in the process of respiration, or breathing. The adduction of the vocal folds and closure of the larynx inhibit air from exiting the lungs and protect the lungs from foreign substances entering them.

Abdominal and Thoracic Fixation Have you ever lifted a heavy box? If you have, you may have noticed something happening at the level of the larynx. Air will not escape through the nose or mouth; most likely, your mouth will be closed. Breathing will stop because the vocal folds adduct, but you feel like you are trying to exhale. Why does this happen? The larynx is considered a valve, and when this valve is closed, it helps to generate adequate abdominal pressure required for heavy lifting. This is known as abdominal fixation. This feeling of a powerful exhale that occurs when the glottis is closed, allowing no air to escape from the mouth or nose, is known as the Valsalva maneuver (as discussed in Chapter 2). In addition to heavy lifting, the Valsalva maneuver helps to generate abdominal pressure for pushing or pulling, childbirth, and bowel movements. There would not be enough pressure to perform these actions without the closure of the laryngeal valve.

Protection During the Swallow Reflex The larynx serves as a protective mechanism during the swallow. Without proper functioning of the larynx, it is likely that food or liquid may “go down the wrong way.” In other words, liquid or food may enter the laryngeal vestibule (penetration) or pass beneath the vocal folds to enter the airway (aspiration). When the swallow reflex is triggered, the hyoid bone is drawn upward and anteriorly, thus pulling the larynx with it in the same direction. This is known as hyolaryngeal excursion. Inversion of the epiglottis as well as hyolaryngeal excursion of true and false vocal fold closure helps to protect the airway and prevent penetration or aspiration.

Throat Clearing and Coughing The larynx serves as a protective mechanism during breathing and swallowing. If, for a variety of reasons, a foreign substance accidentally enters the larynx, trachea, or lungs, the larynx helps to eject the substance through throat clearing and coughing. A healthy cough reflex is stimulated when food or liquids come into contact with the vocal folds. Coughing starts with a deep inhalation through abducted vocal folds followed by the tight adduction of the vocal folds and elevation of the larynx.

➤ Phonation Phonation, or the production of voice, is a complex process. For voicing to occur, three subsystems need to work together to produce sound. These subsystems include n

a power source

n

oscillators (source)

n

resonance chambers (filter) These three coordinative structures are also commonly known as the power, source, and filter of vocal fold vibration (Figure 5–1).

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Coordinative Structures of Voice Power Airflow from the lungs generates the power (or power source) for voice. The diaphragm, chest, abdominal muscles, and chest cavity work together to exhale air from the lungs and move the airstream to the trachea. The air then passes through the vocal folds, causing them to vibrate and produce sound.

Source The larynx is the oscillator, also known as the source because it is the location of vocal fold vibration. Housed within the larynx are the vocal folds. For voice production to occur, air passes through the vocal folds and causes them to vibrate (about 100–1,000 cycles per second) to produce a buzzing sound (e.g., a mouthpiece of a trumpet). The analogy of a mouthpiece of a trumpet and the buzzing sound of the vocal folds is often used to explain how human voice production works. In a trumpet, the mouthpiece is responsible for converting the player's breath into a buzzing sound, which then travels through the instrument and creates a musical tone. Similarly, in the human voice, the vocal folds act as the "mouthpiece" that converts the airflow from the lungs into a buzzing sound, which is then shaped and resonated by the vocal tract to create speech or singing. Without the vocal folds, air would flow freely and unimpeded from the lungs to the oral cavity.

Filter The resonators (or filter) include all the structures above the vocal folds. These include the sinuses, mouth, nose, and pharynx. The buzzing sounds that are generated when air passes through the vocal folds are modified and shaped by these resonating structures and result in the voices we hear when someone speaks or sings. Each individual has a unique vocal tract shape. At the level of the vocal folds, the sound produced is just a buzzing sound; it is this individualized shape of the vocal tract that creates a person’s distinct vocal quality as vibrations pass through it.

FIGURE 5–1. Power, source, filter. Reproduced with permission from Anatomage.

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➤ Theories of Phonation There are several theories of phonation: the myoelastic-aerodynamic theory, the body-cover theory, and the nonlinear source-filter coupling theory.

Myoelastic-Aerodynamic Theory Though this theory has been discussed since the mid-1800s, it was thoroughly detailed by van den Berg in 1958. The basis of the myoelastic-aerodynamic theory (Table 5–1) of voice production is that vibration of the vocal folds is dependent on n

muscle action

n elasticity n pressure n airflow

The action of two key intrinsic laryngeal muscles, the lateral cricoarytenoid and thyroarytenoid (Figure 5–2), is used to approximate the vocal folds so that they are nearly adducted. During this closed phase of vocal fold vibration, air pressure from the lungs builds up underneath the vocal folds (known as subglottic pressure). When the subglottic pressure gets too great, it forces the vocal folds open. The vocal folds open from the bottom to the top (the bottom edges of the vocal folds come apart before the upper edges). At this point, the subglottic pressure is greater than the pressure above the vocal folds, which separates the medial edges of the vocal folds, and air passes upward through the glottis (pressure always travels from areas of high pressure to low pressure). This is known as the open phase of vibration. The open phase is controlled by air pressure from the lungs. The Bernoulli effect, an aerodynamic principle, plays a major role in this theory. The Bernoulli effect states that as air passes through a point of constriction (the glottis), the velocity of airflow increases, resulting in a decrease in pressure. This increase in velocity of airflow through the glottis combined with negative pressure sucks the vocal folds back together. Just as the vocal folds open from the bottom to the top, they also close from the bottom to the top; the bottom edges come back together before the top edges (Figure 5–3). The elastic property of the vocal folds also helps to return the vocal folds to their

TABLE 5–1.

Elements of Myoelastic-Aerodynamic Theory Myoelastic-Aerodynamic Theory

Myo (muscle)

Vocal folds are adducted due to contraction of the intrinsic muscles of the larynx; excluding the posterior cricoarytenoid.

Elastic

The elastic properties of the vocal folds return them to their original shape after being stretched, compressed, and deformed.

Aerodynamic

Force of pressure and resulting flow as the air passes through the glottis. The Bernoulli effect is also part of the aerodynamic process.

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closed phase, which allows this vibratory process to continue in a cyclical pattern (as long as adequate pressure is maintained). The minimum amount of pressure necessary to sustain vibration of the vocal folds is known as the phonation threshold pressure (Chan et al., 1997; Titze et al., 1995). The rapid opening and closing of the vocal folds occur in a cyclical manner because of the airstream. This is referred to as the mucosal wave (Figure 5–3). The air that escapes is converted to sound and is modified by the vocal tract. The Bernoulli effect (Figure 5–4) can be further explained in the following way: Have you ever seen a car pass a truck on the road? The phenomenon includes velocity (V) and absolute pressure (P). When the car is passing the truck, the air that passes between the car and the truck moves in a narrow passage and must increase its speed (V2 > V1). This causes the pressure between them to drop (P1 < P0 ). The pressure is greater on the outside and subsequently pushes the car and truck together. The similar phenomenon occurs for vocal fold opening and closing.

FIGURE 5–2.  Lateral cricoarytenoid and thyroarytenoid. Reproduced with permission from Anatomage.

FIGURE 5–3.  Mucosal wave.

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FIGURE 5–4.  Bernoulli effect.

Body-Cover Theory The general idea of the body-cover theory of phonation is that the structure of the vocal folds plays a role in their vibration. Vahabzadeh-Hagh et al. (2018) revisited this theory, proposed by Hirano (1974) and further investigated by Story and Titze (1995), and concluded that the vocal folds have a n

cover that vibrates and includes the epithelium and superficial layer of the lamina propria (Figure 5–5)

n

transition zone that includes the vocal ligament (Figure 5–5)

n

body called the thyroarytenoid muscle that is made up of two muscle bellies (thyrovocalis and thyromuscularis) (Figure 5–5)

The nature of vibration of the cover is a wavelike pattern that travels from the bottom to the top in different sections. When the different sections of the cover vibrate, it creates different areas of airflow that come together (converge) and separate (diverge) as air flows through the glottis. The convergent airflow has greater air pressure than the divergent airflow, creating a vertical phase difference between sections of the cover. According to this theory, it is the vertical phase difference that maintains the oscillations of the vocal folds. To summarize voice production, there are several steps that are involved. The myoelastic-aerodynamic theory (which includes the Bernoulli effect) and the body-cover theory are involved in voice production. The abdominal muscles, thoracic muscles, diaphragm, and rib cage move air from the lungs toward the vocal folds. The vocal folds subsequently are set in motion and vibrate because of the action of laryngeal muscles, cartilages, and nerves. This vibratory cycle occurs repeatedly as the air from the lungs opens the bottom of the vocal folds and then moves to open the top of the vocal folds. As a result of the

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FIGURE 5–5.  Thyroarytenoid muscle.

fast-moving air that opens the vocal folds, low pressure forms at the tail of the air column and produces the Bernoulli effect. This results in the closure of the bottom of the vocal folds and then closure of the top of the vocal folds. The cycle repeats itself with a puff of air released during each vibratory cycle, which results in voicing (buzzing sound). The sound is then modified and amplified by the resonators in the vocal tract and results in the sound that we hear perceptually.

Nonlinear Source-Filter Coupling Theory Traditionally, the relationship between the source and filter was considered linear — the source (vocal folds and their vibration) was considered to be independent of the filter (the vocal tract). Titze (2008), however, describes a nonlinear relationship between the source and the filter, called the nonlinear source-filter coupling theory. The theory indicates that pressure changes in the filter influence the production of frequencies by the source. This means that positive feedback from above and below the level of the vocal folds can affect how they vibrate. This theory attempts to explain how the source (vocal fold vibration) can be affected by changes in the filter (vocal tract). According to the theory, our vocal tracts act as a vibrating chamber that will vibrate at specific frequencies, which are called resonant frequencies. The resonant frequencies of the vocal tract are referred to as formant frequencies (Lammert & Narayanan, 2015). As the buzzing sound from the vocal folds travels through the vocal tract, the frequencies that most closely match the vocal tract’s formant frequencies will be amplified, while others will be attenuated. In the traditional linear source-filter theory, the vocal tract filters the source frequency but does not play a role in how it is produced. As long as the source frequency is below that of the formant frequencies, the source will be only slightly influenced by the filter, which is why it was long believed that an interaction between the source and filter was linear. Recent literature, however, indicates that human voices can follow either a linear or nonlinear path of interaction. Maxfield et al. (2017) showed that variations in the vocal tract, or filter, influence the fundamental frequency and harmonics — both products of the source.

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➤ Parameters of Voice Parameters of voice are the ways the vocal folds, larynx, and structures of the vocal tract move and influence different characteristics of phonation.

Elasticity, Stiffness, and Inertia The vocal folds are matter; therefore, they are subject to different properties of matter. The properties we are most concerned with are elasticity, stiffness, and inertia because of their role in vocal fold vibration: n

Elasticity is a material’s ability to return to its original size and shape when a distorting force is removed. The simplest example of this property is a rubber band’s ability to return to its original size and shape after it has been stretched out. Vocal folds rely on their elastic property to come back together during phonation.

n

Stiffness is the degree to which a material resists a deforming force. Glass has a high stiffness because it can break easily, but it cannot be as easily bent and deformed. Regarding phonation, as the vocal folds are lengthened, there is an increase in tension and stiffness — mainly in the epithelial layer. Increasing vocal fold stiffness contributes to a faster vibratory rate, which is then perceived as a higher-pitched voice.

n

Inertia refers to the tendency for an object in motion to stay in motion or an object at rest to stay at rest unless acted upon by an outside force. These properties play a large part in the myoelastic-aerodynamic theory of phonation.

Because voicing is a balance between pressure, airflow, and acoustics, there are several different parameters that contribute to vocal quality. These parameters can generally be divided into aerodynamic and acoustic parameters.

Acoustic Parameters When you hear the word “acoustics,” what do you think of? Words like “acoustic guitar” may pop into your head. Acoustics is the branch of physics that deals with the properties of sound.

Fundamental Frequency The number of vibratory cycles that occur per second (cycles per second) is known as the frequency of vocal fold vibration, and it is measured in hertz (Hz). For example, if the vocal folds complete 100 vibratory cycles per second, the frequency is 100 Hz. If the vocal folds vibrate 350 cycles per second, the frequency is 350 Hz. A full vibratory cycle for the vocal folds is one open phase and one closed phase; therefore, a frequency of 100 Hz would mean the vocal folds are completing the open and closed cycle 100 times per second. On average, men, women, and children have different vocal fold vibratory cycles when they speak: n

men:  110 to 180 cycles per second or hertz

n

women:  180 to 220 cycles per second or hertz

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children:  300 cycles per second or hertz

Fundamental frequency (F0 ), also called the fundamental, is the lowest frequency of a vibrating body and is the primary frequency of vibration of the vocal folds. Various aspects impact fundamen174

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tal frequency, such as the size, length, and tension of the vocal folds. From the fundamental we get harmonics, which are whole-number multiples of the fundamental (e.g., 2 × F0, 3 × F0, 4 × F0, . . .). If the fundamental is 200 Hz, then the harmonics would be 400 Hz, 600 Hz, 800 Hz, and so on. Fundamental is a property of the source — the vocal folds. To change the fundamental, a person needs to change the frequency of the open and closed phase cycle: n

frequency:  vibratory cycles per second

n

fundamental frequency (fundamental): lowest and primary frequency of vibration of the vocal fold

n

harmonics: whole-number multiples of the fundamental frequency

n pitch

The perceptual correlate of frequency is pitch (Figure 5–6). Pitch is not a wholly objective physical property since the way a person perceives pitch can differ from person to person; however, if frequency increases or decreases, so does pitch. It is the subjective property people use to judge whether a sound is “high” or “low.” As the vocal folds vibrate at a faster rate, the frequency is higher and results in the perception of a higher pitch (Brackett, 1947; Hollien, 1960; Moore, 1937). There are many mechanisms of pitch change (Figure 5–7), including lengthening and tensing the vocal folds. n

Pitch range (fundamental frequency range) is the difference between the highest and lowest frequencies produced by a specific set of vocal folds. Healthy vocal folds (Figures 5–8 and 5–9) are able to undergo a fundamental frequency change of approximately two octaves. Pitch range can be either shortened due to pathologies, such as vocal nodules, polyps (Figure 5–10), or

FIGURE 5–6.  Pitch. In the image, A is at a lower (male) fundamental frequency, and B is at an increased (female) fundamental frequency, which would be perceived as a higher pitch. The arrow indicates the increase of pitch from A to B for /e/.

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FIGURE 5–7.  Mechanisms of pitch change.

Reinke edema (Figure 5–11) that change the anatomy or physiology of the vocal folds, or expanded through training of the vocal mechanism. Hemorrhagic vocal polyps are common benign lesions of the vocal fold. They are usually located on the anterior two thirds of the vocal folds and appear more often in men than in women. Hemorrhagic polyps mainly occur because of chronic or acute mechanical phonotrauma to the superficial layer of lamina propria. Capillary bleeding within the superficial layer of the lamina propria may be caused by a hyperfunctional voice disorder and may result in rupture of the neovascularized mass. Hemorrhagic polyps are surgically removed. n

Optimal pitch or frequency refers to the ideal frequency of vocal fold vibration that requires the least amount of effort for an individual. It is the frequency that is the most efficient and natural for the anatomical and physiological aspects of a larynx. Optimal pitch is a function of vocal fold mass and elasticity and varies by age and gender. An adult female will generally have a higher optimal pitch than an adult male because of a difference in vocal fold mass and length. As a male child goes through puberty, the larynx grows considerably, causing the vocal folds to increase in mass. The vocal folds lengthen and thicken with a subsequent deeper voice when speaking. 176

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FIGURE 5–8.  Healthy vocal folds — open. Anterior commissure denotes the anterior portion of the larynx. Source: Thomas L. Carroll, MD.

FIGURE 5–9.  Healthy vocal folds — closed. Anterior commissure denotes the anterior portion of the larynx. Source: Thomas L. Carroll, MD.

n

Habitual pitch should not be mistaken for optimal pitch. Habitual pitch is the frequency of vibration that is used most regularly and often by an individual. It would be ideal if the habitual pitch was the same as the optimal pitch; however, this may not always be the case because of conscious or unconscious reasons. Although a habitual pitch that is higher or lower than an optimal pitch may not necessarily be indicative of, or the cause of, a voice disorder, it can still negatively influence efficiency and effort of phonation. More effort is required as the vocal folds 177

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FIGURE 5–10. Hemorrhagic polyp: interoperative view. Anterior commissure denotes the anterior portion of the larynx. Source: Thomas L. Carroll, MD.

FIGURE 5–11. Reinke edema: interoperative view. Anterior commissure denotes the anterior portion of the larynx. Source: Thomas L. Carroll, MD.

are pushed to the boundaries of their range. This extra effort results in less efficient phonation and greater vocal fold fatigue. n

Pitch is the perceptual correlate of frequency. It is the subjective property of how “high” or “low” a sound is perceived.

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Pitch range is the difference between the highest and lowest frequencies for a specific set of vocal folds. 178

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Reinke Edema The medical term edema means “swelling.” Reinke edema, also known as polypoid corditis, polypoid degeneration, or diffuse polyposis, occurs when the superficial layer of the lamina propria (the “Reinke space”) becomes filled with fluid due to trauma or prolonged exposure to such irritants as cigarette smoke (Dewan et al., 2022). Perceptual signs of Reinke edema include a lowered pitch as a consequence of increased vocal fold mass and hoarseness. Reinke edema is sometimes more noticeable in women due to an apparent lowered voice. Other symptoms may include breathlessness because of the swelled vocal folds partially blocking the airway.

n

Optimal pitch is the most efficient and natural frequency for the anatomical and physiological features of an individual’s larynx.

n

Habitual pitch is the frequency of vibration that is most regularly used by an individual.

Amplitude and Intensity When you want to speak to a friend in a busy restaurant, you will most likely try to make your voice louder. Increasing the loudness of your voice feels natural in these types of settings; however, the term “loudness” is based on multiple vocal fold processes: n

Amplitude is the degree or magnitude of displacement of a particle from its mean position or resting state. Figure 5–12 depicts amplitude. In the case of sound waves, we are specifically dealing with air particles, or how much an air particle is displaced. While pitch is the perceptual correlate of vocal fold frequency, amplitude is perceptually experienced as loudness. A sound is perceived as louder if amplitude is increased and softer if amplitude is decreased. Amplitude of vibration refers to the degree of lateral excursion of the vocal folds from the midpoint.

n

Sound intensity is the amount of power transferred by sound waves per unit area in a direction perpendicular to that area. Power is energy per second. The decibel (dB) is the unit used to measure intensity of a sound wave. The energy of a wave is proportionally related to amplitude; therefore, the intensity of a wave is also proportionally related to amplitude. If amplitude increases, so will intensity. If intensity decreases, amplitude will decrease. If intensity is increased or decreased, loudness will also be increased or decreased. Loudness, then, is the perceptual correlate of both amplitude and intensity:

FIGURE 5–12. Amplitude.

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Vocal Fold Movement and Intensity Changes An increase in medial compression of the vocal folds, or how tightly they are pushed together, will increase subglottic pressure. If there is more pressure below the vocal folds, it will result in an increase in sound intensity. This increase in medial compression can be achieved through contraction of the muscles of adduction, such as the interarytenoid and lateral cricoarytenoid muscles. When the vocal folds are more tightly compressed, more force is required to blow them open. They also close quicker and have a tendency to stay closed for a longer period because they are so tightly compressed. The amount of force required to retain this state is greater; therefore, when the vocal folds are released from this state, during the open phase, the sound that is produced is stronger.

n

amplitude:  the magnitude of displacement of a particle from its resting place

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amplitude of vibration:  the degree of lateral displacement of the vocal folds from the midline

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sound intensity:  the amount of power transferred by sound waves per unit area in a direction perpendicular to that area

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decibel (dB):  the unit of measurement for sound intensity

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loudness:  the perceptual correlate of amplitude and intensity

Aerodynamic Parameters The aerodynamic aspects of phonation deal with the properties of gas in motion as well as the interactions between the gas in motion and solid bodies moving through it. The term aerodynamics is commonly used when discussing airplanes; however, you read earlier in the chapter that the Bernoulli effect is a major aerodynamic principle that is involved in speech production. Aerodynamics in relation to phonation can be divided into airflow and air pressure, but it is the relationship between the two that allows for phonation to be possible.

The Bernoulli Effect and Venturi Tube Effect Named after the Swiss mathematician and physicist, Daniel Bernoulli, the Bernoulli effect (Figure 5–13) states that an increase in the speed of a fluid, such as air, occurs simultaneously with a decrease in the fluid’s pressure. The Italian physicist Giovanni Battista Venturi later applied the Bernoulli effect to fluid flowing through a constriction. As fluid flows through a constriction in a tube, its speed increases, which in turn decreases its pressure. We experience these effects as we speak; however, unlike the glass tube Venturi experimented with, our tube is our vocal tract, and one of the points of contraction is at the level of our vocal folds. As air passes through our glottis, it speeds up, which decreases the pressure. This negative pressure that is created then sucks the vocal folds back together. The blue dots in Figure 5–13 represent molecules of air; when molecules of air are closer together, they move slower; when molecules of air are farther apart, they move faster (lower pressure). When air

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FIGURE 5–13.  Bernoulli effect.

moves faster through the glottis, the air molecules are farther apart, and subsequently, there is less force exerted on the vocal folds.

Airflow When we talk about airflow during phonation, we are referring to the air that blows through the vocal folds. How much air we allow to escape through the glottis will determine the sound of our voice. If glottal closure is incomplete, perhaps due to polyps, the voice may sound breathier because of an excess in airflow. Airflow originates from the lungs; as such, if a person has respiratory problems, it will negatively affect phonation.

Subglottic Air Pressure Before phonation can occur, a buildup of pressure below the level of the vocal folds is needed. The area below the level of the vocal folds is known as the subglottic space (Figure 5–14). Pressure is created by airflow from the lungs and adduction of the vocal folds. First, the muscles of respiration cause a flow of air from the lungs to the larynx. Then, the lateral cricoarytenoid and interarytenoid muscles adduct the vocal folds to the midline. This adduction of the vocal folds creates a barrier to the airflow so that it becomes trapped in the subglottic space. As airflow builds up in the subglottic space, it generates pressure against the inferior surface of the vocal folds, which is known as subglottal pressure. This subglottic pressure blows open the vocal folds during phonation. Proper regulation of subglottic pressure is dependent on sufficient control of lung volume and muscle activity (Traser et al., 2020).

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FIGURE 5–14.  Subglottic space.

➤ Variations in Vocal Fold Closure Patterns, Mucosal Wave, and Periodicity of Vibration In the case of many voice disorders, there may be differences in vocal fold closure patterns, the movement of the mucosal wave, and the periodicity of vibration. It is important, therefore, to examine what is considered “normal” vocal fold vibration as well as what is considered “abnormal.”

Vocal Fold Closure In the case of normal, healthy vocal folds, there is an even amount of closure when the vocal folds are adducted. In the case of vocal fold lesions (i.e., polyps, cysts, vocal fold nodules, etc.), however, the vocal folds may not be able to evenly adduct because of the gap created by the lesion. These abnormal closure patterns can be anterior gaps, posterior gaps, hourglass shaped, or spindle shaped. There is an anterior gap in the vocal fold closure pattern if there is a gap near the anterior commissure of the vocal folds (toward the vocal folds’ attachment with the thyroid cartilage). The vocal folds only close posteriorly, usually due to a posterior lesion. In Figure 5–15, the large vocal fold granuloma prevents the vocal folds from meeting anteriorly, creating an anterior gap. If there is an anterior gap, excess air will escape through the glottis during phonation, creating a breathy voice quality. There is a posterior gap in the vocal fold closure pattern if there is a gap near where the vocal folds attach to the arytenoid cartilages at the vocal process. A lesion on the anterior portion of the vocal folds may create a posterior gap. As with an anterior gap, there is also a breathy voice quality because air will escape through the glottis during phonation. In Figure 5–16, the vocal fold polyp creates a posterior gap. An hourglass shape is created when there are both anterior and posterior gaps; therefore, there is only medial vocal fold closure. The best example of an hourglass closure pattern is seen with vocal nodules 182

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FIGURE 5–15. Granuloma. Anterior commissure denotes the anterior portion of the larynx. Source: Thomas L. Carroll, MD.

FIGURE 5–16.  Vocal fold polyp: interoperative view. Anterior commissure denotes the anterior portion of the larynx. Source: Thomas L. Carroll, MD.

(Figure 5–17), which are bilateral, symmetrical, and formed in the middle/anterior two thirds of the vocal folds. Air will also escape through the glottis during phonation, resulting in a breathy voice quality. Figure 5–17 depicts an hourglass-shaped gap. A spindle shape occurs when there is incomplete vocal fold closure (Figure 5–18) along the entire length of the vocal folds. The spindle shape is usually associated with vocal fold atrophy and bowing. Figure 5–18 shows a spindle-shaped gap. 183

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FIGURE 5–17.  Vocal nodules: interoperative view. Anterior commissure denotes the anterior portion of the larynx. Source: Thomas L. Carroll, MD.

FIGURE 5–18.  Incomplete vocal fold closure. Anterior commissure denotes the anterior portion of the larynx. Source: Thomas L. Carroll, MD.

Movement of the Mucosal Wave The mucosal wave is the lateral, longitudinal, and vertical wavelike displacement, also known as a traveling wave, of the superficial tissue of the vocal folds during phonation. The lower edges of the vocal folds open first, followed by the upper edges, and air passes through. The mucosal wave is dependent 184

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on vocal fold structure; therefore, any modifications to that structure can cause mucosal wave abnormalities (Krausert et al., 2011). The mucosal wave can be described as being full, partial, or absent. Healthy vocal folds will produce a full mucosal wave, while abnormalities may cause a decrease or absence of the mucosal wave. There may be variations in the mucosal wave even in healthy individuals. An absent mucosal wave may be caused by stripping of the superficial lamina propria, severe scarring, or other pathologies. The mucosal wave is best observed through a form of high-speed image capture. One type of highspeed image capture technology is digital laryngostroboscopy. Through laryngostroboscopy, the larynx is imaged with a strobe light. The strobe light flashes at a rate of 5 microseconds and captures images of the vocal folds. For example, older Disney movies had animations similar to laryngostroboscopy. An animation is created from separate images flipped through quickly to make one smooth motion. Laryngostroboscopy is similar; however, thousands of images of the vocal folds are captured and combined and played like a slow-motion video. Videokymography is another type of digital recording technique that uses a reference line that is transverse to the glottis and allows high-speed sampling up to 8,000 frames per second. The purpose of videokymography is to visualize vibratory cycles of vocal fold vibration. With this technique, it is possible to observe propagation of mucosal waves, the motion of the upper and the lower margins of the vocal folds, as well as left–right asymmetries. High-speed digital videoendoscopy is another type of digital recording technique for viewing vocal fold vibration that allows sampling rates up to 2,000 to 4,000 frames per second (Hertegård, 2005). Unlike laryngostroboscopy, which is only an impression of continuous vibration, high-speed digital videoendoscopy allows for real-time viewing of both periodic and aperiodic vocal fold vibration. High-speed videoendoscopy is the only technique that captures the true intracycle vibratory patterns via a sequence of full-frame images of the vocal folds.

Regularity and Periodicity of Vibration Vibration is periodic (Figure 5–19), which means it repeats itself each cycle. Earlier, you read about frequency (i.e., how often something happens), whereas period is the time it takes for something to happen. The time it takes to complete one cycle of vibration is period of vibration. Vibration is periodic so long as the time it takes to complete each cycle repeats itself, and the pattern of vibration remains the same. The human voice is quasi-periodic — meaning that the pattern of vibration is similar but not identical from cycle to cycle. Conversely, if vibration is aperiodic (Figure 5–20), the time it takes to complete each cycle is inconsistent.

FIGURE 5–19.  Periodic vibration.

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FIGURE 5–20.  Aperiodic vibration.

Whether a vibration is regular or irregular depends on the motion of the vocal folds. For example, vocal folds with irregular vibration may still be periodic if the time it takes to complete a cycle of vibration stays the same and the irregular pattern of motion is consistently repeated. Both periodicity and regularity of vocal fold vibration can be affected by different pathologies. Phonation considered aperiodic or irregular is often associated with voice disorders.

Perturbation, Jitter, and Shimmer (Acoustic Parameters of Voice) Perturbation is a disturbance in the regularity of a waveform and correlates to a harsher vocal quality. Perturbations are a variability in an otherwise periodic waveform. Jitter is a measurement of frequency instability (variability) in cycle-to-cycle fundamental frequency. Shimmer is the measurement of amplitude instability. A normal voice has a small amount of both jitter and shimmer; however, an excess of either can be indicative of a voice disorder.

Vocal Register There are multiple definitions that have been proposed for a vocal register. In 1840, Manuel García defined vocal registers as a series of succeeding sounds of equal quality on a scale from low to high, produced by the application of the same mechanical principle. Hollien (1974) suggested that a vocal register is a series or range of consecutive phonated frequencies that can be produced with nearly identical voice quality, and the mechanism is laryngeal in action. Vocal registers derive from the laryngeal mechanism that includes the mode of vibration. The mode of vocal fold vibration is a precise pattern that the vocal folds can move during a vibratory cycle and is usually restricted within a particular pitch range. If phonation goes outside the limits of the range, the mode or pattern of vibration will be altered to adapt to the following range. Some consider this

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Countertenors and Castrati Anthony Roth Costanzo is a countertenor, which means he sings in a high voice (i.e., a woman’s range); however, he can produce low notes as well (e.g., baritone). Countertenors are trained to only bring a portion of the vocal folds together and leave a part that does not vibrate — this results in a rich operatic sound. In contrast, a castrato (castrati) has only a high-sounding voice. These castrati maintained their high voices because they were castrated before puberty to prevent their voices from deepening and changing. Their resonating chambers were similar to an adult, but the vocal folds were akin to a boy soprano. Since the larynx is a hormone-dependent organ, in teenage boys, an increase in the production of testosterone results in the thickening and lengthening of the vocal folds. Castration before puberty, however, resulted in a decrease in testosterone so that the high voices of these castrati were maintained. References to castrati first appeared in the Vatican chapel choir books in 1599. This coincided with the advent of the first operas that were written for them by Verdi, Handel, Vivaldi, and other composers. The castrati brought opera to the public in 1624 in Venice, and for the next 100 years, the castrati were the best-paid singers in Europe — ensuring the success of operas. The practice of castrating boys so that they could be exploited to sing was banned by the papal states in 1870.

alteration in the mode of vibration to be another definition of vocal register. Commonly referred to registers include n

modal register n pulse register or glottal fry n falsetto

Modal Register The modal register or modal phonation pattern of vocal fold vibration produces a fundamental frequency used most often during everyday speech. It is considered the “normal mode” of vocal fold vibration, and during this pattern, the vocal folds are neither relaxed nor stretched. As pitch rises in this register, the vocal folds become less compliant as they become elongated, stiffer, and their edges thinner. A wide range of both frequencies and intensities are possible in this register; these ranges vary among individuals.

Pulse Register Pulse register or glottal fry is produced on the lower end of the frequency scale (approximately between 30 and 80 Hz) and has a crackling quality similar to what popcorn or frying bacon sounds like. It has higher airflow values than a modal register (Blomgren et al., 1998) and has a longer closed phase of vibration. During the production of a pulse register, Timcke et al. (1958) found the vocal folds to open and close twice in rapid succession and then remain closed for a long period. This pattern of vibration is known as “syncopated rhythm.” When producing this register, the lateral portion of the vocal folds is tensed, resulting in good medial compression and short, thick vocal folds. The majority of the vocal fold moves very little, with mainly the flaccid glottal margins moving in a floppy manner. Pulse register is usually the pattern likened to a rough or harsh voice quality.

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Whistle Register If you ever heard singers produce a sound similar to that of the upper notes of a flute or even a whistle, they may have been using whistle register. This register produces a fundamental frequency higher than falsetto register and is more a product of turbulence rather than a patterned mode of vibration. It can occur at frequencies as high as 2500 Hz and is typically produced by females. With vocal training, male tenors and countertenors may also be able to phonate in the whistle register.

Falsetto Falsetto register is produced with thin, tense vocal folds on the higher end of the frequency scale. Falsetto register is above the modal register but also overlaps it by approximately one octave. The perception of falsetto register is a high-pitched, breathy, and flutelike voice. Compared to modal register, the degree or amplitude of vocal fold movement is reduced. Contact is made briefly between the vocal folds, and vibration occurs mainly on the edges.

Sustained Phonation and Attack Phonation is accomplished through three steps or adjustments of the vocal mechanism. The onset of vibration requires the vocal folds to approximate, or adduct, and move into the stream of airflow. This action is referred to as vocal attack or onset. After this, the vocal folds may remain in a fixed position during phonation. Sustained phonation is phonation that is steadily held out for a relatively long duration at a specific tone. Sustained phonation can be used during voice evaluations to detect vocal tremors and other types of instability in phonation. Vocal fold termination or offset is then achieved by abducting the vocal folds once more. There are three types of vocal attacks or vocal onsets: simultaneous vocal attack, breathy vocal attack, and glottal vocal attack. During simultaneous vocal attack or onset, adduction of the vocal folds and the initiation of expiration occur simultaneously. A simultaneous vocal attack produces a smoother onset of phonation. Breathy vocal attack or onset occurs when airflow begins prior to adducting the vocal folds. This type of attack can be as obvious as hearing a distinct /h/ sound before phonation, as in the name “Harry,” or as subtle as hearing a slight trace of the /h/ sound in the word “why.” The breathy vocal attack is considered breathier and lighter. The third type of vocal attack is glottal vocal attack or onset. During this attack, the vocal folds are adducted prior to the initiation of airflow. This type of attack can be produced when saying “Ah.” You may even be able to feel your vocal folds open. All three vocal attacks may be used in everyday speech. Vocal attacks, however, can also be misused by putting too much force into glottal attacks and causing vocal fold damage.

Linguistic Aspects of Phonation Just as important as the acoustic and aerodynamic features of phonation are the linguistic aspects. Messages are not only conveyed through the ability to speak but also through the use of stress and intonation. 188

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The suprasegmental properties of speech, also referred to as prosody, include pitch, duration, and variations in loudness to convey meaning. These aspects of speech belong to a syllable or a word and cannot be analyzed as discrete segments. Stress is an emphasis given to a word or syllable in a phrase or sentence through the use of an increase in fundamental frequency, intensity, and duration. Intonation refers to the changes in pitch during an utterance to communicate meaning. As an example of how important the linguistic aspects of speech are, consider the phrase “You will want some cake.” If you said that phrase with an increase in stress on “You,” it may indicate that part of the phrase is especially important. However, if you increased stress on “will,” the phrase may sound more like a demand rather than a simple remark. The linguistic aspects of speech not only help convey further meaning to utterances, but they also add to the ultimate naturalness of speech. Consider someone with a monoloud voice, without variations in loudness, or monopitch, without variations in pitch. Monopitch speech is highly correlated to decreased speech naturalness (Anand & Stepp, 2015). These aspects can occur in people with motor speech disorders such as spastic or flaccid dysarthria. Although these speakers are able to articulate all the words, there is something missing in the voice. Speech is considered natural to a listener so long as it follows the listener’s standards for linguistic features such as rate, rhythm, intonation, stress, and patterning along with syntactic structure (Yorkston et al., 1999).

➤ Chapter Summary The larynx, which is considered a part of the lower respiratory system and is involved in the process of respiration, is known as the “voice box”; however, it serves many biological functions as well, including breathing, abdominal fixation, protection during the swallow reflex, throat clearing, and coughing. Abdominal fixation and the Valsalva maneuver both occur to generate adequate pressure required for heavy lifting, as well as to generate abdominal pressure for pushing or pulling, childbirth, and bowel movements. Hyolaryngeal excursion occurs when the swallow reflex is triggered; the hyoid bone is drawn upward and anteriorly resulting in the larynx moving in the same direction, which helps prevent penetration or aspiration. If penetration or aspiration were to happen, the vocal folds help to eject the substance through throat clearing and coughing. Aside from these biological functions, phonation, or the production of voice, occurs when three subsystems work together: a power source, oscillators (source), and resonance chambers (filter). These three subsystems work together to produce voice. The power is generated from the lungs, the source is the location of vocal fold vibration, and the filter encompasses all of the structures above the vocal folds (i.e., sinuses, mouth, nose, pharynx). The air from the lungs passes through the vocal folds causing them to vibrate, and this vibration is then shaped and modified by the resonating structures to create voice. There are several theories of phonation: the myoelastic-aerodynamic theory, the body-cover theory, and the nonlinear source-filter coupling theory. The myoelastic-aerodynamic theory states that the vibration of the vocal folds is dependent on muscle action, elasticity, pressure, and airflow. Two important intrinsic laryngeal muscles within this theory are the lateral cricoarytenoid and thyroarytenoid that are responsible for the movement to approximate the vocal folds. The Bernoulli effect is an important aerodynamic principle in this theory as well. The body-cover theory states that the structure of the vocal folds plays a role in their vibration. The nonlinear

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source-filter coupling theory states that pressure changes in the filter influence the production of frequencies by the source. There are a few acoustic parameters of voice: fundamental frequency, pitch, and amplitude and intensity. Frequency is the number of cycles per second that occur during vocal fold vibration; the perceptual correlate of frequency is pitch. Harmonics are multiples of the fundamental frequency. A person’s optimal pitch is the vocal fold frequency that requires the least amount of effort for an individual, while the habitual pitch, which may be different, is the pitch used most regularly by an individual. The amplitude of vocal fold vibration refers to the degree of lateral excursion from the midpoint, and intensity is the amount of power transferred by a sound wave. Both amplitude and intensity are perceived as loudness. The aerodynamic parameters deal with the properties of gas in motion and interactions between gas and motion and solid bodies moving through it. Airflow refers to how much air escapes through the vocal folds; the higher the airflow, the breathier the voice will sound. A buildup of pressure, called subglottic pressure, is needed to blow open the vocal folds during phonation, creating sound. When vocal fold closure is affected (such as by lesions including polyps, cysts, vocal fold nodules, etc.), abnormal closure patterns can be created. These include an anterior gap, posterior gap, hourglass shape, or spindle shape. The mucosal wave, or traveling wave, is the superficial tissue of the vocal folds that can vibrate laterally, longitudinally, or vertically. This can be either full, partial, or absent, and can be observed by laryngostroboscopy or videoendoscopy. The period of vibration is the time it takes to complete one cycle of vibration; this can be periodic (consistent) or aperiodic (inconsistent). The mode of vocal fold vibration is a precise pattern that vocal folds can move during a vibratory cycle, and this creates the vocal register. The modal register is used during everyday speech, where the vocal folds are neither relaxed nor stretched. Pulse register, or glottal fry, sounds crackly; falsetto register has a high frequency and sounds breathy. Whistle register has an even higher frequency than falsetto and sounds similar to a flute. Vocal attack refers to the onset of vibration of the vocal folds. Sustained phonation, or phonation that is steadily held for a long duration, occurs after the vocal attack. There are three types of vocal attacks: breathy vocal attack, glottal attack, and simultaneous attack. A breathy attack occurs when airflow begins prior to adducting vocal folds, a glottal attack occurs when vocal folds are adducted prior to the initiation of airflow, and a simultaneous attack occurs when adduction and initiation of airflow occur simultaneously. The suprasegmental properties of speech include pitch, prosody, intonation, and variations of loudness. Stress is the emphasis on words or syllables, intonation is the change in pitch, and prosody refers to speech’s stress and intonation pattern. Someone with a monopitch would not have variations in pitch, just as someone with a monoloud voice would not have variations in loudness. Speech is to be considered natural to a listener so long as it follows the listener’s standards for these patterns.

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➤ References Anand, S., & Stepp, C. E. (2015). Listener perception of monopitch, naturalness, and intelligibility for speakers with Parkinson’s disease. Journal of Speech, Language, and Hearing Research, 58(4), 1134–1144. https://doi.org/10.1044%2F2015_ JSLHR-S-14-0243 Blomgren, M., Chen, Y., Ng, M. L., & Gilbert, H. (1998). Acoustic, aerodynamic, physiologic, and perceptual properties of modal and vocal fry registers. Journal of the Acoustical Society of America, 130(5), 2649–2658. https://doi.org/10.1121/​1.422785 Brackett, I. (1947). An analysis of the vibratory action of the vocal folds during the production of tones at selected frequencies (PhD dissertation). Northwestern University. Chan, R. W., Titze, I. R., & Titze, M. R. (1997). Further studies of phonation threshold pressure in a physical model of the vocal fold mucosa. Journal of the Acoustical Society of America, 101(6), 3722– 3727. https://doi.org/10.1121/1.418331 Dewan, K., Chhetri, D. K., & Hoffman, H. (2022). Reinke’s edema management and voice outcomes. Laryngoscope Investigative Otolaryngology, 7(4), 1042–1050. https://doi.org/10.1002/lio2.840 García, M. (1840). The art of singing. Oliver Ditson. Hertegård, S. (2005). What have we learned about laryngeal physiology from high-speech digital videoendoscopy? Current Opinions of Otolaryngology– Head and Neck Surgery, 13(3), 152–156. https:// doi.org/10.1097/01.moo.0000163451​.98​079.ba Hirano, M. (1974). Morphological structure of the vocal cord as a vibrator and its variations. Folia Phoniatrica et Logopaedica, 26(2), 89–94. https:// doi.org/10.1159/000263771 Hollien, H. (1960). Some laryngeal correlates of vocal pitch. Journal of Speech and Hearing Research, 3, 52–58. https://doi.org/10.1044/jshr.0301.52 Hollien, H. (1974). On vocal registers. Journal of Phonetics, 2, 125–143. https://doi.org/10.1016/ S0095-4470(19)31188-X Krausert, C. R., Olszewski, A. E., Taylor, L. N., McMurray, J. S., Dailey, S. H., & Jiang, J. J. (2011). Mucosal wave measurement and visualization techniques. Journal of Voice, 25(4), 395–405. https://doi.org/10.1016%2Fj.jvoice.2010.02.001 Lammert, A. C., & Narayanan, S. S. (2015). On shorttime estimation of vocal tract length from formant

frequencies. PLOS ONE, 10(7), e0132193. https:// doi.org/10.1371/journal.pone.0132193 Maxfield, L., Palaparthi, A., & Titze, I. R. (2017). New evidence that nonlinear source-filter coupling affects harmonic intensity and fo stability during instances of harmonics crossing formants. Journal of Voice, 31(2), 149–156. https://doi.org/​ 10.1016/j.jvoice.2016.04.010 Moore, P. (1937). Vocal fold movement during vocalization. Speech Monographs, 4, 44–55. https://doi​ .org/10.1080/03637753709390051 Story, B. H., & Titze, I. R. (1995). Voice simulation with a body-cover model of the vocal folds. Journal of the Acoustical Society of America, 97(2), 1249–1260. https://doi.org/10.1121/1.412234 Timcke, R., Von Leden, H., & Moore, G. P. (1958). Laryngeal vibrations: Measurements of the glottic wave: Part I. The normal vibratory cycle. Archives of Otolaryngology, 68, 1–19. https://doi​ .org/10.1001/archotol.1958.00730020005001 Titze, I. R. (2008). Nonlinear source-filter coupling in phonation: Theory. Journal of the Acoustical Society of America, 123(5), 2733–2749. https:// doi​.org/10.1121%2F1.2832337 Titze, I. R., Schmidt, S. S., & Titze, M. R. (1995). Phonation threshold pressure in a physical model of the vocal fold mucosa. Journal of the Acoustical Society of America, 97(5 Pt. 1), 3080–3084. https://doi.org/10.1121/1.411870 Traser, L., Burk, F., Özen, A. C., Burdumy, M., Bock, M., Blaser, D., . . . Echternach, M. (2020). Respiratory kinematics and the regulation of subglottic pressure for phonation of pitch jumps — a dynamic MRI study. PLOS ONE, 15(12), e0244539. https://doi.org/10.1371/journal.pone.0244539 Vahabzadeh-Hagh, A. M., Zhang, Z., & Chhetri, D. K. (2018). Hirano’s cover-body model and its unique laryngeal postures revisited. Laryngoscope, 128(6), 1412–1418. https://doi.org/10.1002​%2​ Flary.27000 van den Berg, J. (1958). Myoelastic-aerodynamic theory of voice production. Journal of Speech and Hearing Research, 1(3), 227–244. https://doi.org/​ 10.1044/jshr.0103.227 Yorkston, K. M., Beukelman, D. R., Strand, E. A., & Bell, K. (1999). Management of motor speech disorders in children and adults (2nd ed.). Pro-Ed.

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6 Anatomy of Articulation, Swallowing, and Resonance

➤ Learning Outcomes Upon completion of this chapter, students will be able to: n

Identify the bones that make up the face and understand how they articulate with one another.

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Identify the bones of the skull and understand how they articulate with one another.

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Identify the divisions and anatomy of the vocal tract.

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Understand the gross anatomy of the tongue, velum, and pharynx.

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Understand the varying types and numbers of teeth, gross anatomy of teeth, as well as general timeline of eruption of deciduous and permanent teeth.

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Identify the muscles of the face, the muscles of the tongue, the muscles of mastication, the muscles of the velum, and the muscles of the pharynx, as well as their origins, insertions, innervations, and possible functions.

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➤ Introduction An in-depth knowledge of the anatomy of the structures responsible for articulation of speech, swallowing, and resonance for the speech-language pathologist is extremely important. More often than not, even a child’s simple articulation disorder cannot be appropriately addressed by a clinician without a clear understanding of the child’s underlying anatomy. This knowledge is foundational for a student’s understanding of most if not all speech, swallowing, and resonatory disorders. This chapter begins by covering the underlying bones of the face and skull that provide the structural bases on which are found the many muscles we use for articulation of speech, mastication, deglutition, and resonance.

➤ Bones of the Face Mandible Commonly referred to as the jawbone, the mandible is a large U-shaped bone of the face containing the lower dental arch (Figure 6–1). At birth, the mandible presents as two bony halves that fuse at midline before the child becomes a year old, thus giving rise to the adult mandible that is regarded as a single, unpaired bone: n

The point of fusion of the two halves of the mandible is referred to as the mental symphysis (Figure 6–2). The suture of the mental symphysis begins at the mandible between the front lower incisors and runs inferiorly.

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The mental symphysis divides near the base of the chin to form a medial bony projection known as the mental protuberance (Figure 6–2).

FIGURE 6–1.  Bones of the face. Reproduced with permission from Anatomage.

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FIGURE 6–2.  A. Mandible in context with skull. B. Mandible in isolation. Reproduced with permission from Anatomage.

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The mental protuberance is characterized by a depression at midline with raised bony projections on either side known as the mental tubercles (Figure 6–2).

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The curved portion of the mandible creating the framework for the lower dental arch is the body of the mandible.

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Posterior to the lower dental arch, the mandible reaches superiorly to articulate with the skull. This perpendicular/vertical portion of the mandible is referred to as the rami (singular: ramus) of the mandible (Figure 6–2).

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The point at which the body of the mandible meets the rami is the angle of the mandible (Figure 6–2).

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The rami each have two superior bony projections separated by the semilunar notch (Figure 6–2). The anterior of these is the coronoid process. The coronoid process (Figure 6–2) is a large, triangle-shaped projection with the primary function to provide an inferior point of attachment for the temporalis muscle, which pulls superiorly on the coronoid process during contraction for raising the mandible.

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The more posterior of these two projections is the condylar process. The condylar processes are smaller than the coronoids, and the primary function of the condylar process is that it provides a point of articulation with the skull. They are vertically continuous with the posterior-most edge of the mandible and are composed of the condylar neck (Figure 6–2) reaching and expanding to the condylar head (Figure 6–2).

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Disorders of Mandibular Development Mandibular hypoplasia, also known as micrognathia (Figure 6–3), is a small and underdeveloped mandible. It does occur with otherwise normal infants and is often corrected during normal development with the normal growth of the mandible. Mandibular hypoplasia also is congenital as a part of chromosomal disorders that create syndromes of abnormal traits. Some of these are cri du chat, Marfan, trisomy 13, and Treacher Collins. If the mandible is small enough, the tongue can obstruct the airway and interfere with breathing (Figure 6–3B) and feeding and later with speech (Becking, 2000; Cooper-Brown et al., 2008).

FIGURE 6–3. Micrognathia.

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On the superior surface of the mandible are sockets in which the teeth of the lower dental arch are held in place. These sockets are known as dental alveoli.

Maxillae Aside from the mandible, the maxillae (singular: maxilla) are the largest facial bones and form what is commonly thought of as the upper jaw (Figure 6–4). These are paired bones of the face that form the upper dental arch, roof of the mouth, the base of and lateral portions of the nasal cavity, as well as a small portion of the orbital cavity. Due to the maxillae largely forming the boundaries of the oral and nasal cavity, the maxillae are important for appropriate speech, mastication, and deglutition: n

The maxillae are very much within the middle of the face. As such, they articulate with nine other bones on the perimeter of the face and skull. Each maxilla articulates with palatine bones, lacrimal bones, nasal bones, the zygomatic bones, the frontal bone, the ethmoid, the inferior nasal conchae, the vomer, and the maxilla on the opposite side. 196

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FIGURE 6–4.  Maxillae. Reproduced with permission from Anatomage.

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Major divisions of the maxillae include the corpus (body) and four other major processes. These major processes are the alveolar, zygomatic, frontal, and palatine processes: The alveolar processes of the maxillae make up the U-shaped portion of these bones that house the dental alveoli for the upper dental arch (Figure 6–4). The alveolar processes of the maxillae are superior to and oppose the lower dental arch of the maxillae. n The zygomatic processes of the maxillae are lateral protrusions above the alveolar processes reaching out to articulate with zygomatic bones (Figure 6–4), the bones of your cheek. If you press your finger on the underside of one of your cheekbones (zygomatic bone) and without moving your finger change the pressure more medially toward your nose, you will be touching the zygomatic process of that maxilla. n The frontal processes of the zygomatic bones reach superiorly above the nasal cavity to articulate with the frontal bone (the bone of your forehead) superiorly and also with the nasal bones (Figure 6–4). The frontal processes can be felt by placing your finger on the lateral side of your nose just medial to your eye. n The portion of the maxillae creating the anterior two thirds of the hard palate (the roof of the mouth) is the palatine processes (Figure 6–5). n

Anatomy of the Hard Palate With the maxillae constituting the anterior two thirds of the hard palate, the last one third of the hard palate is composed of the palatine bones that the maxillae articulate with via the palatine processes (Figure 6–5): n

Each of the paired maxilla fuse with the opposite maxilla’s palatine process at a midline suture known as the intermaxillary suture (Figure 6–5).

n

Just posterior to the upper central incisors, the intermaxillary suture expands into the incisive foramen (Figure 6–5), a small hole in the hard palate through which blood vessels and nerves pass to serve nasal tissues. 197

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FIGURE 6–5.  Hard palate. Reproduced with permission from Anatomage.

n A

premaxillary suture is between each lateral incisor and cuspid and runs posteriorly to meet medially at the incisive foramen (Figure 6–5).

n

The premaxillary sutures create the division of the hard palate known as the premaxilla (Figure 6–5).

Etiologies for cleft lip and palate (Figure 6–6) are numerous, but it often occurs as a simple failure in prenatal development of the embryo, resulting in a lack of fusion of the lips or bone along the premaxillary or intermaxillary suture. Cleft lip and cleft palate are conditions that negatively affect normal feeding and the development of normal speech (Shkoukani et al., 2014) and as such are extremely important points of study for speech-language pathologists. In the most developed countries, cleft lip and palate is repaired surgically at a very young age. However, the baby must successfully take a bottle and feed prior to the surgery, and it is the role of the speech-language pathologist to evaluate the child and provide appropriate interventional strategies to allow the infant to seal the lips/oral cavity around a bottle or the mother’s breast and orally transfer milk or formula posteriorly to the pharynx for swallowing.

Cleft Palate The premaxilla is an important structure for the speech-language pathologist because clefting of the lip and anterior hard palate most often occurs along the premaxillary sutures. Cleft lips occur in the soft tissue anterior to the premaxillary sutures (Figure 6–6C). If the cleft continues into the hard palate, it occurs along a premaxillary suture unilaterally for a unilateral cleft (Figure 6–6D) or bilaterally for a bilateral cleft (Figure 6–6E). Clefting of the lip does occur at midline, but it is very rare. Clefts of the premaxillary sutures are referred to as clefts of the anterior palate. If the cleft continues along the intermaxillary suture, it is known as a cleft of the posterior palate. Posterior palate cleft can occur in isolation without anterior clefting of the lip or premaxilla (Figure 6–6B).

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Anatomy of Articulation, Swallowing, and Resonance FIGURE 6–6.  A. Unilateral cleft of lip. B. Posterior cleft of palate. C. Unilateral cleft lip with posterior cleft of palate. D. Full Unilateral cleft lip and cleft palate. E. Bilateral cleft lip and palate.

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Zygomatic Bones The zygomatic bones are the bones of the face that we think of as our cheekbones (Figure 6–7). These bones are small and paired: n

The zygomatic bones are roughly square in shape with a corpus (body) and four processes where they articulate with other bones. These processes are the frontosphenoidal, maxillary, temporal, and orbital processes: n

n

n

n

n

The frontosphenoidal processes of the zygomatic bones reach superiorly to form the lateral portion of the orbital cavities (Figure 6–7). The maxillary processes reach medially to fuse with the maxillae at the zygomatic processes of the maxillae (Figure 6–7). The temporal processes proceed laterally to fuse with the temporal bones at the zygomatic processes of the temporal bones (Figure 6–7). This junction between the zygomatic and temporal bones forms the structure of the cheekbones and is known as the zygomatic arch. The orbital processes of the zygomatic bones reach posteriorly from the superior portion of the zygomatic bones to form the anterior floor plate of the orbital cavities (Figure 6–7).

The zygomatic bones articulate with the maxillae, frontal bones, sphenoid, and temporal bones.

Nasal Bones The nasal bones are two narrow and long bones that are fused at midline to create the bridge of the nose (Figure 6–8). These bones articulate superiorly with the frontal bone, posteriorly with the perpendicular plate of the ethmoid bone, and inferiorly with the maxillae (Figure 6–8).

FIGURE 6–7.  Zygomatic bones. Reproduced with permission from Anatomage.

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FIGURE 6–8.  Nasal bones. Reproduced with permission from Anatomage.

Palatine Bones The palatine bones are complex, small bones on the posterior of the maxillae forming the posterior portions of walls of the nasal cavity, part of the orbital cavity, and the posterior one third of the hard palate (Figure 6–9A): n

The palatine bones are characterized by horizontal plates and perpendicular plates. n The horizontal plates of the palatine bones are the posterior one third of the hard palate. These are fused anteriorly with the palatine processes of the maxillae. Posteriorly, the horizontal plates of the palatine bones provide a point of attachment and anchor for the soft palate. Run your tongue posteriorly back along the roof of your mouth until you feel the hard portion give way. That is where the posterior of the horizontal plate of the palatine bones give way to the soft palate. n Proceeding vertically from the horizontal plates are the perpendicular plates of the palatine bones (Figure 6–9B). n At the peak of each perpendicular plate is the orbital process that forms part of the orbital cavity (Figure 6–9B).

Inferior Nasal Conchae The lateral walls of the nasal cavity are created by small, scroll-shaped bones that articulate anteriorly with the maxillae and posteriorly to the palatine bones and are known as the inferior nasal conchae (pronounced: con shay) (Figure 6–10): n

Along with the middle and superior nasal conchae of the ethmoid, these bones are also referred to as the turbinates.

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B A FIGURE 6–9.  A. Palatine bones in context with other facial bones; B. Palatine bones in isolation. Reproduced with permission from Anatomage.

FIGURE 6–10.  Inferior nasal conchae. Reproduced with permission from Anatomage.

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The three sets of nasal conchae reach and curl into the nasal cavity. The nasal conchae are covered in highly vascularized mucosal linings that air contacts during inspiration and expiration. As inspiratory air passes over these warm and wet mucosal linings of the nasal conchae, the inspiratory air is warmed and humidified to condition it for the lungs.

Vomer

Lacrimal Bone The lacrimal bones are situated medially and anteriorly within the orbital cavity (medial to your eyes) and are named due to their proximity to the tear ducts and other soft tissue structures involved in the production of tears (Figure 6–12): n

These are the smallest bones of the face, and it is often said they are so delicate in appearance as to resemble fingernails.

n

The lacrimal bones articulate superiorly with the frontal bone, inferiorly with the maxilla and inferior nasal conchae, and posteriorly with the ethmoid.

n

These bones form an anterior medial portion of the orbital cavity.

FIGURE 6–11.  Vomer. Reproduced with permission from Anatomage.

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The vomer is a thin, unpaired triangle of bone resting medially and vertically on the floor of the posterior nasal cavity (Figure 6–11). This bone forms the posterior and inferior section of the nasal septum that divides the nasal cavity into left and right halves at midline.

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 6–12.  Lacrimal bones. Reproduced with permission from Anatomage.

➤ Bones of the Skull All the bones discussed to this point have been bones underlying the structure of the face, which holds the mandible, teeth, and eyes. The bones that fuse and articulate with one another to form the cranium, the cavity that holds the brain, are the bones of the skull (Figure 6–13). These include the ethmoid, sphenoid, frontal bone, parietal bones, occipital bone, and temporal bones.

Ethmoid Deep to the maxillae is a complex, unpaired bone at midline known as the ethmoid (Figure 6–14). The ethmoid is a difficult bone to visualize because it is largely situated behind the maxillae. If one were to remove the maxillae, the ethmoid would be remaining deep to where the nasal bones and frontal processes of the maxillae were: n

The ethmoid forms a boundary between the nasal cavity and the cranium. It forms an inferior anterior portion of the cranium, a posterior superior boundary of the nasal cavity, and medial posterior portions of the orbital cavities.

n

The ethmoid is deep and central, articulating with many bones of the face as well as bones of the skull. The ethmoid articulates with the maxillae, palatines, vomer, nasal bones, inferior nasal conchae, lacrimal bones, frontal bones superiorly, and sphenoid posteriorly.

n

The ethmoid has four primary anatomical divisions (Figure 6–14B): the crista galli, the perpendicular plate, the ethmoidal labyrinths, and the horizontal plate, also known as the cribriform plate: n n

Superiorly at midline, the crista galli protrudes into the cranial space (Figure 6–14B). The perpendicular plate projects inferiorly at midline to articulate with the vomer and form the anterior superior bony nasal septum (Figure 6–14B). 204

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FIGURE 6–13.  Bones of the skull. Reproduced with permission from Anatomage.

A

B

FIGURE 6–14.  Ethmoid bone. Reproduced with permission from Anatomage.

n

n

Branching off superiorly from the perpendicular plate are the ethmoidal labyrinths (Figure 6–14B). Portions of these structures are the winglike middle and superior nasal conchae. The horizontal plate forms the horizontal process from which the crista galli projects superiorly into the cranium (Figure 6–14B). The horizontal plate of the ethmoid has tiny foramen through which pass the olfactory nerve on its way from the olfactory sensory receptors in the nose to the brain. 205

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Frontal Bone The frontal bone is a large, unpaired bone that makes up the forehead and the anterior superior portion of the cranium (Figure 6–15): n

The frontal bone overlays the frontal lobes of the brain.

n

At birth, the frontal bone is divided into two bones by a midline suture known as the frontal suture or metopic suture that helps the baby’s head fit through the birth canal and then solidifies into bone with age.

n

The frontal bone consists of three major sections: squamous, nasal, and orbital portions: n

n n

The squamous section is the portion that makes up the forehead (Figure 6–15): n Inferiorly, the squamous portion is characterized by the superciliary arches that form the superior bony portion of the orbital cavities. n Following the superciliary arches laterally, the frontal bone proceeds inferiorly with zygomatic processes that articulate with the zygomatic bone. The nasal portion constitutes the superior bony portion of the nose (Figure 6–15). The orbital portion makes up the superior portion of the orbital cavities holding the eyes (Figure 6–15).

Parietal Bones Posterior to the frontal bone are the paired parietal bones that are medially fused to form the majority of the roof of the cranium (Figure 6–16): n

The paired parietal bones overlay the paired parietal lobes of the brain.

n

The parietal bones articulate with the frontal bones, occipital bones, temporal bones, and sphenoid (Figure 6–16).

FIGURE 6–15.  Frontal bones. Reproduced with permission from Anatomage.

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FIGURE 6–16.  Parietal bones. Reproduced with permission from Anatomage.

n

The medial suture fusing the parietal bones together is known as the sagittal suture (Figure 6–16). Posteriorly, the parietal bones fuse with the occipital bone at the lambdoidal suture (Figure 6–16).

n

Inferiorly, the parietal bones articulate with the squamous portion of the temporal bones and sphenoid at the squamosal suture.

Temporal Bones Inferior to the parietal bones, forming a lateral inferior portion of the cranium are the temporal bones (Figure 6–17). The temporal bones overlay the temporal lobes of the brain: n

The temporal bones are composed of four sections: mastoid process, squamous portion, petrous portion, and tympanic portion (Figure 6–17): n

n

n

n

The mastoid process is the posterior inferior-most section of the temporal bone (Figure 6–17). If you put your finger behind your earlobe, you will feel the mastoid process. The mastoid process provides an attachment point for many muscles and has foramen through which arteries and veins pass. The squamous portion fans superiorly to form the portion of the cranium you may know as your temple (Figure 6–17). The squamous portion fuses superiorly with the parietal bone, anteriorly with the sphenoid, and posteriorly with the occipital bone (Figure 6–17). The petrous portion of the temporal bone is seen interiorly within the cranium. It is a triangular/pyramid-shaped portion of bone housing the cochlea and semicircular canals within. The petrous portion also makes up part of the base of the skull that is known as the endocranium and is an extremely dense and hard bone. The tympanic portion of the temporal bone lies inferior to the squamous portion and forms the bony walls of the external auditory meatus (the ear canal) (Figure 6–17). 207

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FIGURE 6–17.  Left temporal bone.Reproduced with permission from Anatomage.

n

Other features of the temporal bone are the zygomatic process, styloid process (Figure 6–17), and mandibular fossa: n

n

n

The zygomatic process of the temporal bone is a thin piece of bone that articulates with the temporal process of the zygomatic bone to form the zygomatic arch (Figure 6–17). The styloid process is a sharp inferior projection providing a point of attachment for muscles (Figure 6–17). The mandibular fossa is the point of articulation on the temporal bone between the condylar head of the mandible and the temporal bone comprising the temporomandibular joint (Figure 6–17).

Occipital Bone The occipital bone makes up the inferior posterior rounded portion of the cranium and overlays the occipital lobes of the brain (Figure 6–18): n

The occipital bone is primarily characterized by the foramen magnum (Figure 6–18), a large hole in the base of the occipital bone through which the medulla passes connecting the rest of the brainstem above to the spinal cord below.

n

The occipital bone articulates with the parietal bones, temporal bones, and the sphenoid (Figure 6–18).

n

On either side of the foramen magnum are the condylar fossa (Figure 6–18). These are two indentations in the occipital bone, each about the size of the pad of your thumb. When the head is tilted backward, the superior facets of the first cervical vertebra, the atlas, come to rest in the condylar fossa.

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FIGURE 6–18.  Occipital bone. Reproduced with permission from Anatomage.

Sphenoid The sphenoid is a large, unpaired bone of the base of the skull (Figure 6–19). It comprises inferior and anterior portions of the cranium and is deep to the ethmoid: n

The location of the sphenoid is difficult to imagine without a model or a visual (Figure 6–19). Imagine the maxillae and zygomatic bones are removed from a skull revealing the ethmoid. If the ethmoid is then removed, it reveals a clear coronal view of the sphenoid.

n

This coronal view reveals the gross anatomy of the sphenoid: the corpus medially and the greater and lesser wings laterally, the lateral and medial pterygoid processes inferiorly (Figure 6–19): n

n

The corpus of the sphenoid is the primary portion of the bone located medially behind the ethmoid from which other structures of the sphenoid project (Figure 6–19). The greater wings of the sphenoid are the largest of the sphenoid projections and extend superiorly and laterally to form a medial inferior portion of the floor of the cranium (Figure 6–19). The greater wings also form the lateral posterior portion of the orbital cavities.

n

The lesser wings of the sphenoid are located superior to the greater wings and are flat, thin, triangles extending from the corpus (Figure 6–19). Superiorly, the lesser wings provide structural support for the frontal lobes of the brain. Inferiorly, they comprise a portion of the posterior orbital cavities.

n

Extending inferiorly from the lateral portions of the corpus are the paired pterygoid processes (Figure 6–19). Each pterygoid process has a lateral and a medial pterygoid plate. The pterygoid processes provide points of attachment for the lateral and medial pterygoid muscles that play a role in mastication.

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FIGURE 6–19.  Sphenoid; in context with skull. Sphenoid; in isolation. Reproduced with permission from Anatomage.

➤ Muscles of the Face The movement of the structures of the face, specifically the lips, allows appropriate articulation, feeding, swallowing, and nonverbal communication via facial expression. A strong knowledge of the muscles of the face and the muscles associated with the lips is, therefore, integral in speech-language pathology. These muscles are innervated by the seventh cranial nerve — the facial nerve. The size and strength of facial muscles vary among individuals based on age and gender. Many of the fibers of these muscles insert directly into the skin, allowing certain muscles to pull discrete creases into the skin upon contraction and resulting in expressions appearing on the face.

Historical Perspective: Duchenne de Boulogne and Facial Expression in Man Any discussion of the facial muscles is not complete without a mention of one of the founders of neurology who took a special interest in identifying the functions of the muscles of the face in expression — Dr. Duchenne de Boulogne. Born in 1806, Duchenne believed that facial expression was the truest way to discern the inner emotions of a person and believed facial expression to be a language of the divine soul given to man by God. Pairing his pioneering work in electrostimulation of muscles with his interest in facial expressions, Duchenne re-created emotional expressions of the face by identifying the facial muscles responsible for producing these movements. Toward this end, Duchenne is well known for electrically stimulating the facial muscles in a handful of his patients to elicit the necessary muscular contractions for the production of emotional facial expres-

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sions (Figure 6–20) (Parent, 2005). Using a then recent invention — the photograph — Duchenne was able to electrically stimulate the muscles of the face and document the expressions produced in his patients. The most well known of these photographs are of a toothless man who had no sensation in his face, so the man felt no pain from the electric currents being delivered (Figure 6–20). Duchenne’s early work underlies much of our knowledge of facial expressions in man.

FIGURE 6–20.  Duchenne de Boulogne. Public domain.

The facial muscles are largely concerned with movement of the lips. Many of the muscles of the face insert into the muscle tissue underlying the lips — the orbicularis oris — contributing to their movements (Figure 6–21). The orbicularis oris is the sphincterlike muscle circling the mouth. All the other muscles of the face associated with the orbicularis oris are categorized according to their direction of insertion into the orbicularis oris.

Historical Perspective:  Facial Expression from Darwin to Ekman Charles Darwin believed that human facial expressions were universal across all ethnicities and cultures (Darwin, 1998 [reprint]). However, Margaret Mead was unsure if Darwin was correct and believed that expressions and emotions varied by culture. Paul Ekman, professor emeritus of psychology at University of California San Francisco and co-discoverer of microexpressions conducted several experiments and concluded that Darwin was indeed correct. Humans all over the world share their emotions using the same facial expressions. In fact, Ekman found that the face displays subtle and even subconscious emotional cues (Ekman, 2003). He developed the Facial Action Coding System (FACS) to interpret which of the muscles of the face were active even when the person who experiences an emotion is unaware of them. These emotions include fear, disgust, sadness, contempt, anger, surprise, and happiness (Ekman & Friesen, 1978).

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FIGURE 6–21.  Muscles of the face. Reproduced with permission from Anatomage.

The muscles of the face contribute to articulation of speech and to feeding through movement of the lips. The facial muscles, however, also permit the display of overt emotions through facial expressions. These muscles allow for the portrayal of inner, even subconscious emotions through involuntary microexpressions (fast, intense expressions of hidden emotions that are less than a quarter of a second long). The major contributions of these muscles to articulation, deglutition, and facial expression are noted in the following discussion of the muscles of the face. The muscles of the face are categorized as the orbicularis oris, and the remaining muscles of the face are categorized by their orientation and action on the lips during contraction. These are the transverse muscles whose fibers course transversely (buccinator, risorius), the elevators that elevate the upper lip or corner of the mouth (levator labii superioris, levator labii superioris alaeque nasi, zygomatic minor, zygomatic major, levator anguli oris), the depressors that depress the lower lip or corner of the mouth (depressor labii inferioris, depressor anguli oris, mentalis), and finally, the parallel muscles with fibers that run parallel to the orbicularis oris (incisivus labii superior, incisivus labii inferior).

The lips are not only mechanical but are also cosmetic to the face. The shape and pigmentation of the lips are frequently noted as a source of social attraction between humans — important for mating. Darwin believed the lips play a vital role as a focal point of perceived beauty of the face and consequent sexual attraction between humans and that this appreciation of the lips is related to our hominid ancestors’ love of brightly colored fruits. Recent research bears this out that humans, apes, and monkeys initially developed the red/green color vision necessary to see the red pigmentation of the lips for the purposes of foraging for food. However, once developed, this ability then doubled with social purposes in selection of mates (Fernandez & Morris, 2007).

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Orbicularis Oris

n

Origin n Corners of the lips

n

Innervation n Cranial nerve VII (facial nerve) mandibular marginal branch n Cranial nerve VII (facial nerve) lower buccal branch

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Course n Each portion of the orbicularis oris courses from one corner of the lips to the other.

n

Insertion n Other facial muscles insert into the orbicularis oris.

n

Function n Contracts for the purposes of sealing off the oral cavity (i.e., closing the mouth during speech or deglutition) or puckering the lips n Producing labial phonemes n Serves as attachment point for other muscles of the face

FIGURE 6–22.  Orbicularis oris. Reproduced with permission from Anatomage.

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Often characterized as a sphincter muscle that is located within the lips, the orbicularis oris comprises oval-shaped fibers that circle the mouth (Figures 6–21 and 6–22). This muscle is made up of intrinsic and extrinsic muscle fibers. The orbicularis oris is responsible for puckering the lips and closing the mouth, such as when sealing the lips around a straw. The orbicularis oris has a superior portion, the orbicularis oris superior, which underlies the upper lip, and an inferior portion, the orbicularis oris inferior, which underlies the lower lip. The points at which the orbicularis oris inferior and orbicularis oris superior meet laterally to form the corners of the mouth are angles of orbicularis oris:

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Transverse Muscles Buccinator The buccinator muscles are the primary muscles of the cheeks (Figure 6–23). They are transverse muscles because they course laterally and insert into the angles of the orbicularis oris (Figure 6–21). The mass of the right and left buccinator makes up much of the mass of the cheeks themselves. They are the deepest of the facial muscles. They are covered by the masseter muscle posteriorly as well as other facial muscles that insert into the orbicularis oris. Contraction of the buccinators prevents food being masticated from falling into the space between the teeth and inside of the cheeks, the buccal cavities.

The buccinators are important muscles for those who play the bugle and are hence sometimes known as the bugler’s muscle. The bugle is a simple brass instrument with no valves or devices that change pitch. The bugler needs to adjust pitch by varying embouchure (adjusting the facial muscles, cheeks, and lips to the mouthpiece). Proper embouchure, specifically using the buccinators appropriately, will produce a clear tone without any strain or damage to the buccinators.

n

Origin n

Originates at a band of ligament coursing between the sphenoid bone and the mandible known as the pterygomandibular raphe/ligament

FIGURE 6–23.  Buccinator. Reproduced with permission from Anatomage.

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Mandible — near the last molars

n

Lateral area of the alveolar process of the maxilla

Innervation n

n

n

From the pterygoid plate of the sphenoid to the internal surfaces of the mandible (mylohyoid line) Horizontally anterior to enter and merge with muscle fibers of the orbicularis oris

Insertion n

n

Cranial nerve VII (facial nerve) buccal branch

Course n

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Angles of the orbicularis oris

Function n

Compression of the cheeks and lips against the teeth to prevent food debris (stasis) from entering the buccal cavities

n

Allows for sucking action important for infant feeding

n

Laterally draw the corners of the mouth

n

Constricts oropharynx

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Mastication

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Holds food between the teeth while chewing

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Forcefully expels air from the mouth

Risorius The risorius muscles are associated with the cheek of the face (Figure 6–24). They are smaller and more narrow than the buccinators. The risorius muscles are important for transverse retraction of the corners of the mouth, which comes into place for smiling: n

Origin n

n

Innervation n

n

n

n

Posterior area of the face along the fascia covering the masseter muscle Buccal branch of cranial nerve VII (facial nerve)

Course n

Anterior/horizontal

n

Fibers run superficial to the buccinator muscle.

n

Fibers run parallel to the buccinator muscle.

Insertion n

Angles of the orbicularis oris

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Merge with muscle fibers of the lower lip

Function n

Retraction of the lips at the corners

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Facial expressions of smiling and laughter

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B

FIGURE 6–24.  A. Risorius anterior view. B. Risorius lateral view. Reproduced with permission from Anatomage.

To test the theory that contraction of the risorius is associated with smiling and that contraction of this muscle may even predispose one to laughter and the underlying emotions associated with laughter, Strack et al. (1988) asked participants in a study to hold a pen in their mouths in two ways (in the lips, which uses the orbicularis oris muscle, or in the teeth, which uses the risorius muscle). A control group only held the pen in their hands. All three groups watched a cartoon and were asked to respond about whether or not they thought the cartoon was funny. Those in the teeth group who were watching the cartoon with the risorius contracted reported that they found the cartoon funnier than the other two groups who did not have their risorius contracted while watching the cartoon. These results suggested that the contraction of the risorius is associated with priming the emotions associated with smiling and laughter. Other studies reported similar results about the risorius muscle (Hager, 1982). These results help explain why, when humans hear and see each other laugh, we often tend to laugh as well. This was the impetus for an Indian physician Dr. Madan Kataria to begin the first laughter yoga club in 1995. Laughter yoga uses volitional smiling and laughter to induce positive emotions. What began as a small club with a few people getting together to laugh has morphed into over 6,000 clubs in 60 countries.

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Elevators Levator Labii Superioris The levator labii superioris course inferiorly toward the upper lip at an angle from above (Figures 6–21 and 6–25). These muscles elevate the upper lip and are also utilized during smiling and laughter:

n

Origin n

Lower margin of the orbit

n

Fibers arise from the maxilla and zygomatic bone.

Innervation n

n

Course n

n

n

Cranial nerve VII (facial nerve) buccal branches Inferiorly

Insertion n

Upper lip between the levator labii superior alaeque nasi and levator anguli oris

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Mid-lateral region of the upper lip

Function n

Elevates the upper lip

Levator Labii Superioris Alaeque Nasi The levator labii superioris alaeque nasi insert medially into the cartilage of the nose and the upper lip at a sharp, almost vertical, angle from above (Figures 6–21 and 6–26). These muscles elevate the upper lip and are also responsible for some movements associated with smiling and also more negative facial expressions:

FIGURE 6–25.  Levator labii superioris. Reproduced with permission from Anatomage.

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FIGURE 6–26.  Levator labii superioris alaeque nasi. Reproduced with permission from Anatomage.

n

Origin n

n

Innervation n

n

Inferiorly and laterally; divides into two slips

Insertion n

n

Cranial nerve VII (facial nerve) buccal branches

Course n

n

Frontal process of the infraorbital margin of the maxilla

Cartilage of the nose and the orbicularis oris superioris

Function n

Elevates the upper lip

n

Opens the nostrils

n

Snarl

n

Facial expressions of disgust, contempt, and disdain When translated from Latin, levator labii superioris alaeque nasi literally means “lifter of the upper lip and the wing of the nose.” Interestingly, it has the longest name of any muscle in the human body. The snarling of the lips and nostrils performed by the contraction of this muscle is associated with the facial expressions of disgust, contempt, and disdain. It is also nicknamed the Elvis muscle because of his elevated upper lip when he sang.

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Zygomatic Minor The zygomatic minor course inferiorly from the zygomatic bones to insert into the lateral portion of the orbicularis oris superioris (within the upper lip) from above (Figures 6–21 and 6–27). These muscles elevate the upper lip and can contribute to the movements of the mouth during smiling: Origin n

n

Innervation n

n

Inferiorly and medially

Insertion n

n

Cranial nerve VII (facial nerve) buccal branches

Course n

n

Facial surface of the zygomatic bone (zygomaticomaxillary suture)

Lateral portions of orbicularis oris superioris (upper lip)

Function n

Elevates the upper lip

n

Facial expression of smiling and laughter

Zygomatic Major The zygomatic major course inferiorly to insert into angles of the orbicularis oris (Figures 6–21 and 6–28). These muscles are largely responsible for the action of retracting the corners of the mouth posteriorly and superiorly for smiling. According to Ekman (2003), when a person has a fake smile, only the zygomatic major moves. Dimples may also occur when there are variations in this muscle:

FIGURE 6–27. Zygomatic minor. Reproduced with permission from Anatomage.

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FIGURE 6–28. Zygomatic major. Reproduced with permission from Anatomage.

n

Origin n

n

Innervation n

n

Obliquely inferior (down) and medially

Insertion n

n

Cranial nerve VII (facial nerve) buccal branches

Course n

n

Lateral to the zygomatic minor on the zygomatic bone

Angles of the orbicularis oris

Function n

Elevates and retracts the corners of the mouth

n

Facial expression of smiling and laughter

Levator Anguli Oris The levator anguli oris (Figure 6–29) course inferiorly to insert into the corners of the orbicularis oris from above. These muscles squeeze the corners of the mouth medially and superiorly together: n

n

Origin n

Canine fossa of the maxilla

n

Lateral to the rim of the nostrils

Innervation n

n

Cranial nerve VII (facial nerve) superior buccal branch

Course n

Inferiorly 220

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FIGURE 6–29.  Levator anguli oris. Reproduced with permission from Anatomage.

n

Insertion n Angles of the orbicularis oris n Function n Raises the corners of the mouth up and medially n Helps in closing the mouth (draws the lower lip up)

Depressors Depressor Labii Inferioris The depressor labii inferioris originate at the oblique line of the mandible near the mental foramen. These muscles insert into the lower lip and depress the lower lip (Figures 6–21 and 6–30). They also help retract the lower lip inferiorly and laterally: n

Origin n Mandible (oblique line) near the mental foramen n Innervation n Cranial nerve VII (facial nerve) mandibular branch n Course n Superiorly and medially n Insertion n Lower lip n Function n Depresses the lower lip n Pulls lower lip down and laterally n Plays a part in the facial expression of frowning 221

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FIGURE 6–30.  Depressor labii inferioris. Reproduced with permission from Anatomage.

Depressor Anguli Oris The depressor anguli oris course superiorly from the mandible to insert into the angles of the orbicularis oris from below (Figures 6–21 and 6–31). These muscles squeeze the corners of the mouth medially and inferiorly, thereby depressing the corners of the mouth. n

Origin n Oblique line — lateral margins of the mandible n Innervation n Cranial nerve VII (facial nerve) mandibular branch n Course n Fanlike vertically superior n Insertion n Upper lip corner and angles of orbicularis oris n Function n Depresses the corners of the mouth n Brings upper and lower lips together n Plays a part in the facial expression of frowning These muscles are associated with frowning — in most cultures, the frown has a negative connotation (Russel, 1994). In 1982, Carnegie Mellon professor Scott Fahlman was the first to use the colon with the left parenthesis to represent the frowning face on the Internet. When the cheeks are involved with a frown, it usually represents an unpleasant reaction (Pope & Smith, 1994).

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FIGURE 6–31.  Depressor anguli oris. Reproduced with permission from Anatomage.

Mentalis The mentalis courses superiorly from the medial portion of the mandible to insert into the inferior lip from below (Figures 6–21 and 6–32). These muscles push the lower lip out and wrinkle the chin. This muscle is often associated with pouting. Interestingly, the mentalis is even active during sleep: n

Origin n

n

Innervation n

n

Inferiorly

Insertion n

n

Cranial nerve VII (facial nerve) mandibular branch

Course n

n

Incisive fossa of the jaw

Skin of the chin (below)

Function n

Raises the lower lip

n

Pulls out the lower lip

n

Wrinkles the chin

n

Plays a part in facial expression of pouting the lip

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FIGURE 6–32.  Mentalis. Reproduced with permission from Anatomage.

Parallel Muscles: Incisivus Labii Superior and the Incisivus Labii Inferior These are other superficial muscles of the integument (skin) in the region of the mouth. They are also known as parallel muscles. The incisivus labii superior originate in the maxilla just above the canine teeth. They are innervated by the lower zygomatic, buccal, and mandibular branches of the facial nerve. Their course is parallel to the transverse fibers of the orbicularis oris of the upper lip and insert laterally to the angle of the mouth. They draw the corners of the mouth up and medially, pucker and round the lips to help with compression and protrusion of the upper lip. The incisivus labii inferior originate in the incisive fossa of the mandible in the region of the lateral incisors. They are innervated by the lower zygomatic, buccal, and mandibular branches of the facial nerve. The course is parallel to those of the transverse fibers of the orbicularis oris of the lower lip and insert into the orbicularis oris. They draw the corners of the mouth downward and medially to help with compression and protrusion of the lower lip.

➤ Supplementary Muscles of Facial Expression There are several supplementary muscles associated with facial expression (Figure 6–33). The epicranius is subdivided into the occipitalis muscle that is involved with wrinkling the forehead and the frontalis muscle that is involved in raising the eyebrows and wrinkling the forehead (to provide expression) (Figure 6–33). The orbicularis oculi consists of the palpebral portion that gently closes the eyelids when blinking, the orbital portion that firmly closes the eyelids when winking, and the lacrimal portion that draws tears to the eyes (Figure 6–33). The corrugator is responsible for wrinkling the forehead during a frown (Figure 6–33). The procerus wrinkles the root of the nose when you smell something bad (Figure 6–33). The platysma is typically considered to be a neck muscle (Figure 6–34). It is broad, flat, and thin and covers a majority of the anterior and lateral areas of the neck and comes into play for many facial expressions: 224

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FIGURE 6–33. Supplementary muscles of facial expression. Reproduced with permission from Anatomage.

FIGURE 6–34. Platysma. Reproduced with permission from Anatomage.

n

Origin n

n

Fascia overlying the deltoid (shoulder) muscles and pectoralis major (chest)

Innervation n

Cranial nerve VII (facial nerve) cervical branch 225

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n

Course n

n

n

Superiorly

Insertion n

The skin near the masseter

n

The corner of the mouth

n

Lower areas of the mandible

n

Under the mental symphysis

Function n

Contracts voluntarily and depresses the mandible

n

Is active when smiling

n

Draws down the lower lip

n

Tenses skin of the neck

n

Helps form expressions of surprise or fright

n

Assists in forced inspiration during high physical exertion.

➤ Cavities of the Vocal Tract The vocal tract is a series of cavities within the neck and head within which voice is produced (Figure 6–35). The human voice is then filtered through the cavities of the vocal tract and is manipulated by structures such as the velum and tongue that act as valves and articulators for the production of speech (Figure 6–35). The vocal tract is important as a pathway for air for the process of respiration but is also important for the production of speech and resonance as well as the process of hydration and nutritional intake (mastication and deglutition). The vocal tract includes the oral cavity, buccal cavities, nasal cavity, pharynx, and larynx (Figure 6–35).

The Oral Cavity The most familiar and visible part of the vocal tract is the oral cavity. This is what most individuals label as their mouth. It is the beginning of the alimentary canal — the digestive and upper respiratory tract that allows our bodies to interact with the environment for the purposes of respiration, hydration, and nutrition. Speech-language pathologists work a great deal providing therapy to those with structural or physiological deficits of the structures in the oral cavity. This therapy is provided for those with difficulty articulating phonemes for speech with oral structures as well as those having difficulty manipulating food or liquids prior to swallowing.

Anatomical Boundaries of the Oral Cavity The oral cavity is considered to begin anteriorly at the lips or front teeth. The lateral boundaries of the oral cavity are the dental arches between which rests the tongue. Superiorly, the oral cavity is bounded by the hard palate and soft palate (velum). Inferiorly, the muscles that make up the floor of the oral cavity, on which the tongue rests, such as the mylohyoid, constitute the inferior boundary of the oral cavity. Posteriorly, the boundary of the oral cavity is demarcated by posterior faucial pillars that are bands of soft tissue on either side of the posterior walls of the oral cavity created by the palatopharyngeus muscles. 226

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FIGURE 6–35.  Vocal tract cavities.

Structures of the Oral Cavity The oral cavity consists of many structures involved in the production of speech, resonance, and mastication. Many of these structures have roles both in the act of speaking and mastication such as the tongue and the teeth that are used during speech for the production of many phonemes but are also used for the manipulation and crushing of food prior to swallowing. Structures of the oral cavity include the tongue, salivary glands, teeth, alveolar ridge, hard palate, velum, anterior faucial pillars, posterior faucial pillars, and palatine tonsils. Tongue.  The tongue is known as a muscular hydrostat, which means it is a mobile structure composed

primarily of muscle tissue (i.e., no bones). The tongue has taste buds that are sensory receptors for taste and allows the perception of bitter, sour, sweet, and salty. In addition to the sense of taste, the tongue is among the most important structures for the production of speech, mastication, and swallowing.

Anatomy of the Tongue n

Gross divisions of the tongue include the apex, dorsum, and base (Figure 6–36): n

n

The apex is the tip of tongue. The apex plays a very active role in the articulation of speech and during mastication, during which it is highly involved in the manipulation of food and liquid in the oral cavity. The dorsum is the portion posterior to the apex of the tongue. The dorsum of the tongue is also known as the blade, and it is located within the oral cavity. 227

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FIGURE 6–36.  Subdivisions of the tongue. Reproduced with permission from Anatomage.

n

The base of the tongue, also called the root, is within the pharyngeal cavity and constitutes the anterior pharyngeal wall.

n

Running lengthwise down the tongue at midline is a crease known as the medial sulcus, or longitudinal medial sulcus, that marks the division between the right and left sides of the tongue (Figure 6–37).

n

A V-shaped groove in the tongue made where the dorsum meets the lingual tonsils is known as the sulcus terminalis. The sulcus terminalis divides the dorsum of the tongue, from the base of the tongue (Figure 6–37).

n

Anterior to the sulcus terminalis are smaller bumplike structures on the tongue known as circumvallate papillae, or vallate papillae, that give the tongue a rough texture and house taste buds and temperature receptors (Figure 6–37).

n

Posterior to the sulcus terminalis on the base of the tongue, are large bumplike structures of lymphoid tissue known as the lingual tonsils. As lymphoid tissue, they have immunological functions (Figure 6–37).

n The

lingual frenulum is a band of epithelial tissue that runs from the underside of the tongue to the floor of the oral cavity (Figure 6–38).

When a child’s lingual frenulum is too short and is attached to the apex of the tongue it can restrict the superior movement of the tongue. This condition is known as ankyloglossia or colloquially as tongue-tie (Figure 6–38). It can affect a child’s articulation of lingual phonemes or feeding but often does not. It can be recognized during an oral motor evaluation when the child protrudes their tongue, and the sides of the tongue are able to protrude more than the tip, where the lingual frenulum is attached, thereby causing the tongue to display a distinctive heart shape on protrusion (Figure 6–38). Anecdotally, it is often mentioned that these children will not enjoy eating peanut butter since it sticks to the roof of the mouth. This is because if the lingual frenulum is tight enough to keep the apex of the tongue from reaching up to articulate with the alveolar ridge for the production of speech, then the apex of the tongue will be unable to retract along the alveolar ridge to scrape off any peanut butter that may be stuck to the roof of the mouth (hard palate).

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FIGURE 6–37.  Anatomy of the tongue. Public domain.

FIGURE 6–38. Ankyloglossia.

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Salivary Glands.  Salivary glands are tissues that produce saliva in the oral cavity for the oral preparation of food prior to a swallow and to maintain appropriate oral hygiene. There are three sets of paired salivary glands: sublingual, submandibular, and parotid (Figure 6–39). Each salivary gland has its own duct that communicates saliva to the oral cavity. The sublingual salivary glands exist beneath the tongue. The submandibular salivary glands are inferior to the posterior of the sublingual salivary glands (Figure 6–39) and produce the majority of saliva for the oral cavity. The parotid glands are large glands located at and wrapped around the ramus of the mandible (Figure 6–39) and are closely associated with cranial nerve VII, the facial nerve. Dentition.  Humans have two sets of teeth that develop, erupt from the gums, and are used through the life span. Our teeth are used for the purposes of mastication and as articulatory surfaces during speech for linguadental phonemes and labiodental phonemes. Dental Arches.  Our teeth are held and housed within the dental arches (Figure 6–40). The upper dental arch is the horizontal curvature of the inferior maxillae in which the upper teeth are located. The lower dental arch is the horizontal curvature of the superior surface of the mandible in which the lower teeth are located. Teeth are held in place within the upper and lower dental arches by the dental alveoli (Figure 6–40), which are the sockets from which the teeth grow and are secured. Anatomy of a Tooth.  The basic anatomy of a tooth consists of the crown, the neck, and the root. The

gums are referred to as the gingiva. The point on the tooth where it meets the gingiva is referred to as the gingival line or colloquially as the gum line: n The

crown of the tooth is the portion of the tooth projecting above the gingiva (the gums) (Figure 6–41). The crown is coated in a hard white substance composed almost entirely of minerals known as enamel.

n The

root of the tooth is the inferior bony projections of the tooth (Figure 6–41) that reach beneath the gingival line into the dental alveolus and secure the tooth in place. The root is coated in a substance known as cementum, which holds the tooth in place.

FIGURE 6–39.  Salivary glands.

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FIGURE 6–40.  Dental arches. Reproduced with permission from Anatomage.

FIGURE 6–41.  Tooth anatomy. Reproduced with permission from Anatomage.

n The n

neck of the tooth is the point at which the crown and root of the tooth meet (Figure 6–41).

Within the tooth is the pulp, which contains associated soft tissue such as blood vessels and nerves.

Types of Teeth n

Humans have four different categories of teeth, each with a specific function. From anterior to posterior, these are incisors, cuspids, bicuspids, and molars: 231

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Incisors are elongated, thin, and quadrilateral with a sharp edge (Figure 6–42). They are used primarily for cutting into food. Incisors are the most anterior and medial teeth on the dental arches. Imagine you were going to bite into an apple, you would place the apple at your open mouth for a bite. This would be anteriorly between the upper and lower dental arches where, upon raising the mandible, your incisors would cut out a bite of the apple. n Lateral to the incisors are the cuspids, also known as the canines. Cuspids are easily distinguishable by their single triangular point (Figure 6–43). Cuspids are used for gripping and tearing food with the teeth. Imagine you were going to take a bite out of a tough steak but lacked a fork and knife. In this case, you probably would not place the steak so much medially to use the incisors, but you would center the steak more laterally between the cuspids, and then, pulling the steak away from your mouth with your hands, rip a bite off. n Bicuspids, also known as premolars (Figure 6–44), are used for grinding food once a portion of food suitable for mastication is in the mouth. n Molars (Figure 6–45) are the primary grinders of food. These are the largest of the teeth with a great deal of surface area between the lower and upper molars used for grinding and chewing food prior to swallowing. n

Deciduous and Permanent Teeth n

The first set of teeth, the deciduous teeth (Figure 6–46), colloquially known as one’s baby teeth, or milk teeth, begin to develop prior to birth and begin the process of erupting from the gums at 8 to 12 months and continue until around 2-and-a-half years of age. The first deciduous teeth to erupt are usually the lower incisors followed by the frontal incisors. n Humans have a total of 20 deciduous teeth. This includes 10 on the upper dental arch and 10 on the lower dental arch (Figure 6–46). There are four incisors, two cuspids, and four molars on each dental arch. n The deciduous teeth tend to erupt in the general order of anterior to posterior beginning with the eruption of the central incisors at around 8 or 9 months and ending with second molars around 2 to 2-and-a-half years of age.

FIGURE 6–42.  Incisors. Reproduced with permission from Anatomage.

FIGURE 6–43.  Cuspids. Reproduced with permission from Anatomage.

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FIGURE 6–44.  Bicuspids. Reproduced with permission from Anatomage.

FIGURE 6–45.  Molars. Reproduced with permission from Anatomage.

FIGURE 6–46.  Deciduous teeth.

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n

The permanent teeth begin the process of erupting and replacing the deciduous teeth around 6 years of age, lasting around 7 years, and the process is complete at around age 11 or 12 years. n The period of time during which a child has a mixture of deciduous and permanent teeth is the mixed dentition stage. n Humans have a total of 32 permanent teeth (Figure 6–47). This includes 16 on the upper dental arch and 16 on the lower dental arch (Figure 6–47). The upper and lower dental arch each has four incisors, two cuspids, four bicuspids (or premolars), and six molars (Figure 6–47). n Humans have more permanent teeth than deciduous teeth. This is because the mandible and maxillae of older and more developed individuals are larger and able to accommodate larger and more teeth. n Most permanent teeth have deciduous analogues they are replacing, but many do not. Permanent teeth that have deciduous analogues, such as the four incisors on each deciduous dental arch and four incisors on each permanent dental arch, are successional teeth. Permanent teeth that do not have deciduous analogues and are entirely new, such as the bicuspids, are superadded teeth. Dental Surfaces.  Different teeth have a varying number of surfaces for which we have to be able to refer: n The

occlusal surface is the surface where the teeth of the upper and lower dental arches come into contact with one another when the mandible is raised. n The surface of the teeth that comes into contact with the tongue is known as the lingual surface.

FIGURE 6–47.  Permanent teeth. Reproduced with permission from Anatomage.

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n

The surface of the anterior-most teeth, the incisors and cuspids, that contacts the inside of the lips is the labial surface.

n

For those teeth more posterior on the dental arch, the buccal surface contacts the inside of the cheeks.

n

For teeth that are side by side on the dental arch, their surfaces in contact with one another are referred to as the approximal surfaces.

use of the teeth is for the process of mastication. For mastication to occur, the teeth of the upper and lower dental arches must be brought together to cut and grind food. The act of raising the mandible to bring the upper teeth into contact with the lower teeth is occlusion. How and to what degree the teeth may be occluded varies according to the specific location and orientation of an individual’s teeth. The differing ways in which the teeth of the upper and lower dental arches meet during occlusion are referred to as the types or patterns of occlusion. Types of occlusion are roughly divided into three categories: Class I, Class II, and Class III. Class I occlusion is considered normal. Classes II and III are known as malocclusions, meaning that the occlusion is imperfect for the act of appropriate mastication. Malocclusion can negatively affect an individual’s ability to masticate but can also negatively affect speech and speech development: n

Class I occlusion (seen in A on Figure 6–48), also known as normal occlusion, is the most appropriate for mastication and is considered the most appropriate relationship between the upper and lower teeth. During Class I occlusion, the upper cuspids are a half tooth’s length behind the lower cuspid, and the upper incisors are just anterior and overlapping the lower incisors.

n

Class II is a malocclusion (seen in B on Figure 6–48) and is characterized by upper cuspids that are directly in line with lower cuspids. During Class II malocclusion, there is often significant overjet of the upper incisors. Overjet is when the maxillary incisors are well anterior to the mandibular incisors.

n

Class III is a malocclusion (seen in C on Figure 6–48), also called prognathism, that is characterized by the first mandibulary molar being anterior to the first maxillary molar. During

FIGURE 6–48.  Types of malocclusions.

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Types of Occlusion.  Although humans use the teeth as an immobile articular during speech, the main

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Class III malocclusion, there is often significant underbite. Underbite is when the mandibular incisors are far anterior to the maxillary incisors. Hard Palate and Velum.  The oral cavity also contains the hard palate that is made up of portions of

maxillae and palatine bones: n

The hard palate anteriorly and the velum posteriorly form the superior boundary of the oral cavity.

n The

hard palate plays a significant role in allowing appropriate mastication of food, provides articulatory surfaces for speech for both alveolar phonemes and velar phonemes and also allows for normal oral resonance.

n

The anterior hard palate has a series of small ridges known as the palatal rugae.

n

Posterior to the hard palate, the soft palate is composed of muscle and soft tissues. The primary role of the velum is to act as a valve to seal off the nasal cavity during deglutition, to keep anything being swallowed from inadvertently ending up in the nasal cavity. The velum also seals off the nasal cavity for appropriate resonance, specifically regulation of nasality during speech to establish nasal and nonnasal phonemes.

n

Posteriorly, the velum ends in a medial fleshy projection that is the uvula. The uvula hangs off the posterior of the velum in the back of the throat and is usually apparent during an oral exam.

Alveolar Ridge.  Immediately posterior to the maxillary incisors is a small protuberance of the anterior-

most section of the hard palate (Figure 6–49) that is the alveolar ridge. If you put the tip of your tongue behind your front teeth at the point where your front teeth meet the roof of your mouth, that is the alveolar ridge. The alveolar ridge is important for appropriate articulation because it is the structure that the tongue contacts during the production of alveolar phonemes such as /t/ and /d/.

FIGURE 6–49.  Structures of the oral cavity.

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Tonsillitis occurs when the palatine tonsils are infected (Figure 6–50). When infected, the palatine tonsils can present as white or red and maybe inflamed and swollen. In severe cases, the swelling of the tonsils can be so great as to threaten occlusion of the posterior oral cavity and create difficulty breathing and swallowing.

FIGURE 6–50. Tonsillitis.

Anterior and Posterior Faucial Pillars.  Posteriorly on the lateral walls of the oral cavity are two columns

of tissue known as the anterior faucial pillars and posterior faucial pillars (Figure 6–49): n

The anterior faucial pillars are the most anterior of these two structures. The anterior faucial pillars are formed by the palatoglossus muscle. This muscle connects the velum to the lateral portions of the tongue.

n

The posterior faucial pillars are commonly considered the posterior boundary of the oral cavity. The posterior faucial pillars are formed by the palatopharyngeal muscle that connects the velum to the pharynx.

n

Between the anterior and posterior faucial pillars are the palatine tonsils (Figure 6–49). The palatine tonsils are pink, fleshy masses of lymphoid tissue on either side of the posterior oral cavity wall.

Buccal Cavities Sometimes considered a part of the oral cavity, the buccal cavities are the spaces between the lateral dental arches, the posterior teeth, and the flesh of the cheeks on each side of the oral cavity. The buccal cavities are important in appropriate oral resonance. You can demonstrate this to yourself by pulling your checks away from your teeth, thereby enlarging the buccal cavities, and producing speech. The 237

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buccal cavities are also important in that the muscles of the cheeks, primarily the buccinators, need to be tensed for the appropriate production of high-pressure labial consonants during speech (/p/, /b/). If the tension in the cheeks is too loose, it makes building up appropriate pressure for production of /p/ and /b/ difficult if not impossible. Appropriate tension to hold the cheeks against the teeth is required during mastication or food will fall inappropriately into the buccal cavities.

Nasal Cavity The nasal cavity extends from the nares, the anterior opening of the nasal cavity at the face, to the nasal choanae, which is the point at which the nasal cavity opens into the pharynx posteriorly (Figure 6–35, p. 227). Laterally, the vertical processes of the maxillae and palatine bones form the walls of the nasal cavity. The floor of the nasal cavity is formed by the horizontal processes of the maxillae and palatine bones. Medially, the nasal cavity is divided into right and left halves by the nasal septum. The nasal cavity has mucosa-lined walls to warm and humidify the inspired air, and the hairs within the anterior portion of the nasal cavity just posterior to the nares assist in filtering the inspired air. For the speech purposes of producing nasal phonemes, the air and sound of phonation are allowed to pass through the nasal cavity by depressing the velum, thereby opening the nasal cavity to the pharynx.

Pharynx The pharynx is a muscular tube commonly called the throat that exists posterior to the nasal cavity and oral cavity (Figure 6–35). Superiorly, the pharynx begins at the base of the skull and extends inferiorly until the level of the lower cervical vertebrae. The diameter of the pharynx is larger superiorly than inferiorly giving it the shape of an inverted cone. The muscular walls of the pharynx constrict during deglutition. The pharynx has three primary regions that extend from the nasal cavity above to the epiglottis and esophagus below. From superior to inferior, these are the nasopharynx, oropharynx, and laryngopharynx: n

Nasopharynx (Figure 6–35) n The nasopharynx is the superior-most portion of the pharynx located behind the nasal cavity and above the velum. n On the posterior wall of the nasopharynx are located masses of lymph tissue known as the adenoids or pharyngeal tonsils. n The eustachian tubes open into the nasopharynx allowing air pressure to equalize between the middle ear and the environment and to also circulate fresh air to the middle ear to prevent infection.

n

Oropharynx (Figure 6–35) n The oropharynx is the section of the pharynx posterior to the oral cavity. n The oropharynx is bounded superiorly by the velum, and the inferior boundary of the oropharynx is at the level of the hyoid bone. n The oropharynx opens anteriorly to the oral cavity. Below the oral cavity, the anterior wall of the oropharynx is the base of the tongue, while the posterior boundary of the oropharynx is the posterior pharyngeal wall, which is visible when you look into the back of your mouth with a flashlight. n The base of the tongue is within the oropharynx as is the vallecula, which is the concave cuplike space that exists between the base of the tongue and the epiglottis. 238

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Hypopharynx or Laryngopharynx (Figure 6–35) n

n

n

n

The most inferior division of the pharynx, closely associated with the larynx, is the hypopharynx or laryngopharynx. The hypopharynx is bounded superiorly at the epiglottis and inferiorly at the level of the esophagus. The epiglottis (Figure 6–35) is a cartilaginous flap that descends to cover the opening to the larynx during a swallow to assist in preventing the aspiration or penetration of food or liquids into the airway. At the base of the hypopharynx is the esophagus (Figure 6–35), which is the collapsed muscular tube, posterior to the trachea, that conducts food and liquids being swallowed from the laryngopharynx to the stomach.

➤ Muscles of the Tongue The tongue is a symmetrical and muscular organ within the oral cavity with a vertical tissue coursing the length of the tongue at midline, called the lingual septum or medius fibrous septum. The lingual septum provides a medial point of attachment for muscles of the tongue. Directly beneath the mucosal layer of tissue on the tongue lies the submucous fibrous layer, which provides a superficial attachment point for muscles of the tongue. Due to the tongue being composed primarily of muscle, it is remarkably agile, and its role in speech, mastication, and swallowing cannot be understated. To fully understand the movements of the tongue, one needs to understand the anatomy of the tongue.

Intrinsic Muscles of the Tongue The muscles of the tongue are generally categorized as intrinsic and extrinsic. The intrinsic muscles of the tongue are the muscles that actually comprise the mass of the tongue (Figures 6–51 and 6–52). They originate within the tongue and terminate within the tongue. The intrinsic muscles of the tongue are responsible for changing the shape of the tongue and fine motor movement of the tongue, such as those movements largely utilized during articulation of speech. These include tongue apex elevation, apex retraction, deviation of the tongue, curling, uncurling, flattening, and narrowing of the tongue. The intrinsic muscles of the tongue include the superior longitudinal muscle, the inferior longitudinal muscle, the vertical muscle, and the transverse muscle (Figures 6–51 and 6–52).

Superior Longitudinal Muscle (Figure 6–51) n

Origin n

n

Insertion n

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The submucous fibrous layer near the epiglottis in the base of the tongue as well as from the lingual septum Into mucosal tissue laterally and at the apex of the tongue

Course n

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Runs the length of the tongue from the base to the tip and is the most superior layer of the muscle on the dorsum of the tongue Fibers course anteriorly and medially toward the lateral edges of the tongue. 239

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FIGURE 6–51.  Superior longitudinal, inferior longitudinal, and vertical muscles of the tongue.

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Innervation n

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The intrinsic muscles of the tongue are all innervated by cranial nerve XII, the hypoglossal.

Function n n

Bilateral contraction elevates the apex of the tongue (Figure 6–51). Unilateral contraction of the tongue will push the apex of the tongue toward the side of contraction.

Inferior Longitudinal Muscle (Figure 6–51) n

Origin n

n

Insertion n

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Into mucosal tissue laterally and at the apex of the tongue

Course n n

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The submucous fibrous layer near the epiglottis in the base of the tongue as well as from the lingual septum

The length of the tongue from the base of the tongue to the apex of the tongue. This muscle resides in the underside of the tongue with fibers of the transverse and vertical muscles between it and the superior longitudinal muscle.

Innervation n

The intrinsic muscles of the tongue are all innervated by cranial nerve XII, the hypoglossal. 240

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Function n Largely opposes the action of the superior longitudinal muscle by pulling the apex of the tongue inferiorly (Figure 6–51). n Like the superior longitudinal muscle, unilateral contraction of the inferior longitudinal will deviate the apex of the tongue to the side of the contraction. n If co-contracting with the superior longitudinal muscle, the inferior longitudinal will assist in retracting the tongue.

Vertical Muscle (Figure 6–51) n

Origin n Superiorly within the dorsum of the tongue on the submucosal fibrous layer n Insertion n At the mucosal layer on the inferior portions of the tongue n Course n From the dorsum of the tongue inferiorly n Innervation n The intrinsic muscles of the tongue are all innervated by cranial nerve XII, the hypoglossal. n Function n Generally opposing the transverse muscle, the vertical muscle pulls inferiorly, thereby flattening and widening the tongue (Figure 6–51).

Transverse Muscle (Figure 6–52) n

Origin n At the lingual septum n Insertion n Into the submucosal tissue in the lateral portions of the tongue n Course n From the lingual septum, the fibers of the transverse muscle course laterally and horizontally to the edge of the tongue. n Innervation n The intrinsic muscles of the tongue are all innervated by cranial nerve XII, the hypoglossal. n Function n When contracted, pulls the lateral portions of the tongue medially, thereby narrowing the tongue (Figure 6–52)

Extrinsic Muscles of the Tongue Whereas the intrinsic muscles of the tongue both originate and insert into the tongue itself, the extrinsic muscles of the tongue originate elsewhere and course to and insert into the tongue (Figure 6–53). 241

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The fibers of the transverse and vertical muscles of the tongue exist within the same space and location. Their fibers interweave with the transverse muscle fibers coursing horizontally, while the fibers of the vertical muscle course between those fibers running vertically.

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 6–52.  Transverse muscle contracts, pulling lateral edges of tongue medially and narrowing tongue.

The extrinsic muscles of the tongue are responsible for gross movement of the tongue. Often, the extrinsic muscles of the tongue can act as a mover of the tongue as well as a mover of the structure of their origin. The extrinsic muscles of the tongue include the genioglossus, hyoglossus, styloglossus, and palatoglossus.

Genioglossus (Figures 6–53 and 6–54) n

Origin n

n

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Insertion n

Superior fibers insert into the dorsum and near the apex of the tongue.

n

Inferior fibers insert at the hyoid.

Course n

n

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On the inner surface of the mandible, behind the chin

Fibers of the superior portion course superiorly from the inner mandibular surface to insert into the dorsum and near the apex of the tongue. Inferior fibers course down to insert into the hyoid.

Innervation n

By cranial nerve XII, the hypoglossal 242

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FIGURE 6–53.  Extrinsic muscles of the tongue. Reproduced with permission from Anatomage.

FIGURE 6–54. Genioglossus. Reproduced with permission from Anatomage. n

Function n The genioglossus is known as the largest and strongest extrinsic muscle of the tongue. It is the primary mover of the tongue. n When the inferior fibers of this muscle contract, it pulls the base of the tongue anteriorly, thereby protruding the apex of the tongue (like when you stick your tongue out). n When the superior fibers of the genioglossus are contracted, they perform the opposite function and work to retract the tongue into the mouth. 243

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When both superior and inferior fibers are contracted simultaneously, they depress the body of the tongue within the oral cavity.

Hyoglossus (Figures 6–53 and 6–55) n

Origin n

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Insertion n

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The hyoglossus courses superiorly, and it reaches upward from the hyoid to insert into the back dorsum of the tongue.

Innervation n

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The submucosal tissue of the sides of the tongue on the posterior half of the dorsum

Course n

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The hyoid bone

Cranial nerve XII, the hypoglossal

Function n

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When used as a mover of the tongue, the contraction of the hyoglossus pulls the tongue downward toward the hyoid; therefore, it pulls the tongue inferiorly and posteriorly. The hyoglossus can also assist in elevating the hyoid.

Styloglossus (Figures 6–53 and Figure 6–56) n

Origin n

n

Styloid process of the temporal bone

Insertion n

The inferior of the sides of the dorsum of the tongue

FIGURE 6–55.  Hyoglossus. Reproduced with permission from Anatomage.

FIGURE 6–56.  Styloglossus. Reproduced with permission from Anatomage.

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Course n The styloglossus courses inferiorly and anteriorly from the styloid process to reach the tongue.

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Innervation n Cranial nerve XII, the hypoglossal

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Function n One can see that by virtue of the location and orientation of the styloglossus that, upon contraction, it pulls the tongue posteriorly and superiorly. In this way, the styloglossus directly opposes and is an antagonist of the genioglossus.

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Origin n Palatal aponeurosis of the velum (discussed later)

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Insertion n The posterior dorsum of the tongue into the sides of the tongue

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Course n Inferiorly from the velum to the back edges of the tongue

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Innervation n The pharyngeal plexus of cranial nerve X, the vagus. n The palatoglossus is the only muscle of the tongue not innervated by cranial nerve XII, the hypoglossal nerve.

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Function n Courses inferiorly along the lateral posterior of the oral cavity to form the anterior faucial pillars n When used as a mover of the tongue, elevates the back of the tongue

FIGURE 6–57.  Palatoglossus. Reproduced with permission from Anatomage.

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Palatoglossus (Figure 6–57)

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➤ Muscles of Mastication Mastication is the process of chewing food. It is the mandible that holds the lower teeth and is able to move these teeth against the upper teeth of the immobile maxillae for this action. Therefore, the muscles of mastication are those muscles associated with the movement of the mandible (Figure 6–58). The mandible can be raised, lowered, protruded and retracted, and lateralized for the purposes of grinding food. The muscles that facilitate these movements are the masseter, temporalis, medial pterygoid, lateral pterygoid, digastricus, mylohyoid, and geniohyoid (Figure 6–58).

Masseter (Figures 6–58 and 6–59) n

Origin n Zygomatic arch of the zygomatic bone n Insertion n Inferior posterior boundary of the ramus of the mandible n Course n This muscle courses inferiorly at a slightly posterior angle from the zygomatic arch to the back of the ramus of the mandible. n Innervation n Mandibular branch of the cranial nerve V, the trigeminal n Function n This muscle is the most superficial of the muscles of mastication. n If you clench your teeth, you can feel the bulk of the flexed masseter behind your check superficial to the ramus of your mandible.

FIGURE 6–58.  Muscles of mastication. Reproduced with permission from Anatomage.

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FIGURE 6–59.  Masseter. Reproduced with permission from Anatomage.

n

Upon contraction, this muscle elevates the mandible, bringing the dental arches in contact with one another and to a lesser degree can also act to protrude the mandible.

Temporalis (Figures 6–58 and 6–60) n

Origin n This muscle originates in a fanlike shape along the side of the skull on an indentation known as the temporal fossa. n Insertion n Coronoid process of the mandible n Course n This muscle courses inferiorly from the side of the skull, beneath the zygomatic arch, to the coronoid process of the mandible. n Innervation n Cranial nerve V, the trigeminal n Function n The temporalis lies deep to the masseter. n Posterior transverse fibers work to retract the mandible. n Anterior vertical fibers function to elevate the mandible.

Medial Pterygoid (Figure 6–61) n

Origin n The medial pterygoid process of the sphenoid 247

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FIGURE 6–60.  Temporalis. Reproduced with permission from Anatomage.

FIGURE 6–61.  Medial pterygoid. Reproduced with permission from Anatomage.

n

Insertion n

n

Ramus of the mandible

Course n

This muscle courses from the medial pterygoid process posteriorly and inferiorly to insert on the medial side of the ramus of the mandible (Figure 6–61). 248

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Innervation n

n

n

Mandibular branch of the cranial nerve V, the trigeminal

Function n

Elevates and protrudes the mandible

n

Unilateral contraction facilitates lateralization for grinding of food during mastication.

Lateral Pterygoid (Figure 6–62) Origin n

n

Insertion n

n

The lateral pterygoid courses posteriorly from the sphenoid to the condylar process (Figure 6–62).

Innervation n

n

Condyloid process of the mandible

Course n

n

Greater wing of the sphenoid and the lateral pterygoid process of the sphenoid

Mandibular branch of the cranial nerve V, the trigeminal

Function n

Works primarily to protrude the mandible

n

Also assists in depressing the mandible

n

Unilateral contraction acts to protrude the mandible in a lateral direction, and this combined with action of the medial pterygoid muscles facilitates a rotary mastication during mastication.

FIGURE 6–62.  Lateral pterygoid. Reproduced with permission from Anatomage.

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Digastricus (Figures 6–58 and 6–63) The digastricus, or the digastric muscle, has two individual portions, known as the anterior belly and posterior belly. Each belly has separate origins, but both insert into an intermediate tendon that joins both to the hyoid. n

n

Origin n

Anterior belly:  Posterior surface of the mandible behind the mental symphysis

n

Posterior belly:  Mastoid process of the temporal bone

Insertion n

n

Course n

n

n

Anterior belly:  The anterior belly courses from its origin behind the mental symphysis posteriorly to the hyoid. Posterior belly:  The posterior belly courses from the mastoid process of the temporal lobe anteriorly and inferiorly to the hyoid.

Innervation n

n

Both the anterior and posterior belly of the digastricus insert into an intermediate tendon connecting both to the hyoid.

Cranial nerve VII, the facial nerve

Function n

Lowers the mandible

FIGURE 6–63.  Digastricus. Reproduced with permission from Anatomage.

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Mylohyoid (Figures 6–58 and 6–64) n

Origin n The inside surface of the mandible

n

Insertion Anterior fibers insert into a medial tendon known as the mylohyoid raphe.

n

Posterior fibers insert directly into the hyoid.

Course n

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Innervation n

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The fibers course medially from the inside surface of the mandible medially and posteriorly to insert into the mylohyoid raphe and the hyoid. Mandibular branch of the cranial nerve V, the trigeminal

Function n

This flat, sheetlike muscle is deep to the anterior belly of the digastricus and forms the floor of the oral cavity.

n

Assists in depressing the mandible

n

Can also assist in raising the hyoid

Geniohyoid (Figures 6–53 and 6–58) n

Origin n

Inner surface of the mandible posterior to the mental symphysis

FIGURE 6–64.  Mylohyoid. Reproduced with permission from Anatomage.

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Insertion n The body of the hyoid n Course n Posteriorly from the back of the chin to the hyoid bone n Innervation n Cervical plexus accompanied by hypoglossal n Function n Assists in depressing the mandible n Can also assist in raising the hyoid The platysma was covered earlier as a muscle of the face, but it can also assist during mastication.

Platysma (Figure 6–34, p. 225) n

Origin n Fascia of the superior thorax n Insertion n The inferior border of the mandible and inferior skin of the face n The platysma is a cutaneous muscle, meaning it is inserted directly into the skin under which it courses. n

Course n From the anterior superior thorax along either side of the neck to the mandible n Innervation n Cranial nerve VII, the facial nerve n Function n A wide, sheetlike anterior and superficial muscle of the neck n Plays a role in facial expression n Assists in depressing the mandible

➤ Muscles of the Velum The velum, also known as the soft palate, is a muscular projection off the posterior hard palate. The function of the velum is to elevate and seal off the nasal cavity from the pharynx during deglutition and nonnasal speech sounds. The muscles of the velum can be thought of as elevators or depressors of the velum. The elevators of velum consist of the levator veli palatini, musculus uvula, and tensor veli palatini, while the depressors of the velum are the palatoglossus and palatopharyngeus. Notice in Figure 6–65 that elevators of the velum originate superiorly and course inferiorly to insert at the velum to be able to elevate it (excluding the musculus uvula). In contrast, those muscles responsible for depressing the velum originate below the velum and course superiorly to insert at the velum to be able to pull down on it. Many of these muscles attach at the velum on a piece of tendinous fibrous tissue arising from the posterior hard palate and coursing through the length of velum, known as the palatal aponeurosis. It is largely through muscular attachments to the palatal aponeurosis that the velum is elevated and depressed. 252

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FIGURE 6–65.  Muscles of the velum.

Elevators of the Velum Levator Veli Palatini (Figure 6–65) n

Origin n Petrous portion of the temporal bone and cartilage of the eustachian tube n Insertion n Palatal aponeurosis of the velum n Course n Inferiorly from its origin to insert into the velum n Innervation n Pharyngeal plexus of cranial nerve X, the vagus n Function n Primary elevator of the velum that makes up much of the mass of the velum

Musculus Uvulae (Figure 6–65) n

Origin n Palatal aponeurosis and posterior nasal spine n Insertion n Mucosal tissue of the velum 253

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n

Course n

n

Innervation n

n

The fibers of the musculus uvula course lengthwise from the origin near the hard palate toward the terminus of the velum. Pharyngeal plexus of cranial nerve X, the vagus

Function n

Shorten and elevate the velum

Tensor Veli Palatini (Figure 6–65) n

Origin n

n

Insertion n

n

Inferiorly and anteriorly from the sphenoid and eustachian tube to the velum

Innervation n

n

Palatal aponeurosis

Course n

n

Medial pterygoid process of the sphenoid and the cartilage of the eustachian tube

Mandibular branch of cranial nerve V, the trigeminal

Function n

Dilates the eustachian tube for aeration of the middle ear

n

Tenses and assists in elevation of the velum

Depressors of the Velum Palatoglossus (Figure 6–65) The palatoglossus runs between the tongue and the velum. As such, it is spoken of as being both a muscle of the velum and a muscle of the tongue. Due to its two attachments, it can function to depress the velum in addition to elevating the tongue. The palatoglossus was also covered earlier as a muscle comprising the anterior faucial arch: n

Origin n

n

Insertion n

n

Inferiorly from the velum to the back edges of the tongue

Innervation n

n

The posterior dorsum of the tongue into the sides of the tongue

Course n

n

Palatal aponeurosis of the velum

The pharyngeal plexus of cranial nerve X, the vagus. The palatoglossus is the only muscle of the tongue not innervated by cranial nerve XII, the hypoglossal nerve.

Function n

In regard to the velum, the palatoglossus depresses the velum. 254

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Palatopharyngeus (Figure 6–65) This muscle runs from the velum to the pharynx and is spoken of as both a muscle of the velum and as a muscle of the pharynx. The palatopharyngeus forms the posterior faucial pillars: Origin n Posterior hard palate and palatal aponeurosis n Insertion n Thyroid cartilage and blends with fibers of superior pharyngeal constrictor n Course n From the velum inferiorly to the pharynx n Innervation n Pharyngeal plexus of cranial nerve X, the vagus n Function n In relation to the velum, this muscle is a depressor of the velum.

➤ Muscles of the Pharynx The pharynx has many structures and functions important for speech, resonance, and swallowing in particular, as the pharynx is the link between the oral cavity and esophagus. The pharynx is also vitally important to the process of respiration, as it is the link between both the nasal and oral cavities and dedicated airway that begins with the larynx. An understanding of the muscles of the pharynx allows for a greater understanding of the function of the pharynx itself. The muscles of the pharynx are divided into the constrictors and the longitudinal muscles.

Pharyngeal Constrictors The pharyngeal constrictor muscles form the lateral and posterior walls of this structure (Figure 6–66). These are the superior, middle, and inferior pharyngeal constrictors, which fit into and are continuous with one another. These muscles form largely the posterior and lateral walls of the pharynx as the anterior of the structure is composed of the epiglottis, the base of the tongue, and the opening of the oral and nasal cavities (Figure 6–66). Working together, these constrictor muscles are responsible for pharyngeal constriction. This is the contraction of the pharynx during swallowing, pharyngeal peristalsis, to assist in safely propelling food and water through the pharynx into the esophagus. The constrictors all insert into a fibrous ligament tissue at the posterior midline on the pharynx known as the pharyngeal raphe. The pharyngeal raphe runs the vertical length of the pharynx.

Superior Pharyngeal Constrictor (Figures 6–66 and 6–67) n

Origin n Pterygoid process of the sphenoid, the inside of the posterior mandible, as well as along a pterygoid-mandibular raphe that provides the point of origin between the pterygoid and mandible bones n Insertion n Pharyngeal raphe 255

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FIGURE 6–66.  Pharyngeal constrictors. Source: Figure 1.13 from Advance Review of SpeechLanguage Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition, (p. 20), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

FIGURE 6–67.  Superior pharyngeal constrictor. Reproduced with permission from Anatomage.

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n

Course n From the sphenoid and mandible posteriorly to the pharyngeal raphe n Innervation n Pharyngeal plexus of cranial nerve X, the vagus n Function n To constrict and narrow the pharynx during deglutition to direct food into the esophagus

Middle Pharyngeal Constrictor (Figures 6–66 and 6–68) Origin n Hyoid n Insertion n Pharyngeal raphe n Course n From the hyoid posteriorly and superiorly to the pharyngeal raphe n Innervation n Pharyngeal plexus of cranial nerve X, the vagus n Function n To constrict and narrow the pharynx during deglutition to direct food into the esophagus

Inferior Pharyngeal Constrictor (Figures 6–66 and 6–69) The inferior pharyngeal constrictor muscle has two primary components reflecting the differing points of origin of the muscle: the thyropharyngeal muscle, also known as the thyropharyngeus, and the cricopharyngeal muscle, also known as the cricopharyngeus.

FIGURE 6–68. Middle pharyngeal constrictor. Reproduced with permission from Anatomage.

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FIGURE 6–69.  Inferior pharyngeal constrictor/thyropharyngeus. Reproduced with permission from Anatomage.

Thyropharyngeal Muscle/Thyropharyngeus (Figures 6–66 and 6–69) n

Origin n

n

Insertion n

n

Inferiorly from the pharyngeal raphe to the thyroid

Innervation n

n

Pharyngeal raphe

Course n

n

Thyroid

Pharyngeal branch of cranial nerve X, the vagus

Function n

To constrict and narrow the pharynx during deglutition to propel food into the esophagus

Cricopharyngeal Muscle/Cricopharyngeus (Figure 6–66) n

Origin n

n

Insertion n

n

Pharyngeal raphe

Course n

n

Cricoid

Inferiorly from the pharyngeal raphe to the cricoid

Innervation n

Pharyngeal branch of cranial nerve X, the vagus 258

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Function n The cricopharyngeal muscle is the ringlike muscle at the top of the esophagus also known as the upper esophageal sphincter (UES). n Remains constricted most of the time to close off the esophagus and prevent gastroesophageal reflux n Relaxes only to allow the esophagus to open and accept food or liquid being swallowed

The group of muscles known as the longitudinal muscles of the pharynx course vertically within the pharynx and function to elevate the pharynx during deglutition (Figure 6–70). The action of elevating the pharynx, larynx, and UES during deglutition allows for the effective sealing off of the airway by the epiglottis, and also for shortening the distance between the oral cavity and the UES to maximize the speed of transitioning food and liquid from the oral cavity, through the pharynx, into the esophagus.

Palatopharyngeus (Figures 6–70 and 6–71) n

Origin n Posterior hard palate and palatal aponeurosis n Insertion n Thyroid cartilage and blends with fibers of superior pharyngeal constrictor n Course n From the velum inferiorly to the pharynx n Innervation n Pharyngeal plexus of cranial nerve X, the vagus

FIGURE 6–70.  Longitudinal muscles of the pharynx. Reproduced with permission from Anatomage.

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Longitudinal Muscles of the Pharynx

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FIGURE 6–71. Palatopharyngeus. Reproduced with permission from Anatomage.

n

Function n In relation to the pharynx, this muscle is an elevator of the pharynx.

Salpingopharyngeus (Figures 6–70 and 6–72) n

Origin n Eustachian tube n Insertion n Fibers of the palatopharyngeus n Course n Vertically from the nasopharynx to blend with the fibers of the palatopharyngeus at the laryngopharynx n Innervation n The pharyngeal plexus of cranial nerve X, the vagus n Function n Elevates the lateral walls of the pharynx during deglutition

Stylopharyngeus (Figures 6–70 and 6–73) n

Origin n Styloid process of the temporal bone n Insertion n Laterally into the walls of the pharynx n Course n At a sharp vertical angle from the styloid to the inferior pharynx 260

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FIGURE 6–72.  Salpingopharyngeus. Reproduced with permission from Anatomage.

FIGURE 6–73. Stylopharyngeus. Reproduced with permission from Anatomage.

n

n

Innervation n

Cranial nerve IX, the glossopharyngeal

n

This is the only muscle of the pharynx not innervated by the vagus nerve.

Function n

Elevates the pharynx 261

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➤ Chapter Summary Several bones of the face articulate with one another to provide the underlying structure required for processes of speech, mastication, and deglutition. The mandible is the jawbone. Features of the mandible include the mental symphysis, mental protuberance, mental tubercles, body of the mandible, the rami, and the semicircular notch. The temporomandibular joint is where the mandible articulates with the temporal bone of the skull providing the joint responsible for elevating and depressing the mandible. Mandibular hypoplasia is a congenital condition featuring a small, underdeveloped mandible. Mandibular hypoplasia can interfere with breathing, feeding, and speech. The maxillae are paired bones of the face that form the upper dental arch, the roof of the mouth, the base, the lateral portions of the nasal cavity, and also a small portion of the orbital cavity. The four major processes of the maxillae are the alveolar, zygomatic, frontal, and palatine processes. The premaxilla is the anterior-most division of the hard palate formed by the maxillae. Clefting of the lip and hard palate often occurs along the premaxillary sutures, left or right, sometimes bilaterally. Clefting of the lip and palate affects normal feeding and speech and requires a surgical repair. The zygomatic bones, or cheekbones, are paired bones containing the frontosphenoidal, maxillary, temporal, and orbital processes. The nasal bones are two narrow and long bones that are fused at midline to create the bridge of the nose. The palatine bones are complex small bones on the posterior of the maxillae. These bones form the posterior portion of the lateral walls of the nasal cavity, part of the orbital cavity, and the posterior one third of the hard palate. The inferior nasal conchae are small, scroll-shaped bones extending from the lateral walls of the nasal cavity. The inferior nasal conchae articulate anteriorly with the maxilla and posteriorly with the palatine bones. The vomer is a thin, unpaired triangle of bone resting medially and perpendicularly on the floor of the posterior nasal cavity. The lacrimal bones are situated medially within the orbital cavity and are named due to their proximity to the tear ducts and other soft tissue structures involved in the production of tears. In addition to the bones that make up the framework that holds the eyes, teeth, and mouth, there are several fused bones that make up the cranium, the skull. The ethmoid is an unpaired bone that forms a boundary between the nasal cavity and the cranium. The frontal bone is a large, unpaired bone that is the forehead and is the anterior and superior portion of the cranium. Posterior to the frontal bone are the parietal bones, which overlay the parietal lobes of the brain. The temporal bones are inferior to the parietal bones and form a lateral inferior portion of the cranium. The temporal bones overlay the temporal lobes of the brain. The sphenoid is a large, complex, unpaired bone of the base of the skull. It consists of the corpus, greater wing, and lesser wing, as well as the lateral and medial pterygoid processes, which are important points of connection for the muscles of mastication. The muscles of the face are important for communication via articulation of speech and facial expression. Several muscles insert into the orbicularis oris, which is the large muscle surrounding the lips. The buccinator and risorius are transverse muscles that course laterally. The buccinators are primarily responsible for compression of cheeks and the lips against the teeth. They help with articulation of pressure consonants such as /p/ and /b/, normal oral resonance, and keeping food out of the buccal cavity. The risorius helps with retraction of the lips at the corners to contribute to smiling as well as laughter. Major elevators of the orbicularis oris include levator labii superioris (elevation of the upper lip), levator labii superioris alaeque nasi (elevation of the upper lip, opening of the nostrils, asso-

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ciated with snarling of the lip seen in facial expressions of disgust), zygomatic minor (elevation of the upper lip), zygomatic major (elevation and retraction of the lips for smiling and laughter), and levator anguli oris (raising the corners of the mouth up and medially and closing the mouth (drawing the lower lip up). Major depressors of the orbicularis oris include depressor labii inferioris (depressing the lower lip and pulling the lips down and out, contributing to the facial expression of frowning) and depressor anguli oris (depressing the corners of the mouth and bringing the upper and lower lips together, contributing the facial expression of frowning). The mentalis is responsible for raising the lower lip and wrinkling the chin and is associated with the facial expression of pouting. The incisivus labii superior are superficial muscles that draw the corners of the mouth up and medially and pucker and round the lips to help with compression and protrusion of the upper lip. The incisivus labii inferior draw the corners of the mouth downward and medially to help with compression and protrusion of the lower lip. Supplementary muscles of facial expression include the epicranius that is involved in wrinkling the forehead and raising the eyebrows; the orbicularis oculi that aids in gently closing the eyelids when blinking, firmly closing the eyelids when winking, and drawing tears to the eyes; the corrugator muscle that is responsible for wrinkling the forehead; and the procerus that is involved with wrinkling the root of the nose. The platysma is a superficial cervical muscle that can act to depress the mandible. It is also active when smiling and draws the lower lip down and tenses the skin of the neck. The vocal tract is a series of cavities within the neck and head within which voice is produced; it includes the oral cavity, buccal cavities, nasal cavity, pharynx, and larynx. The oral cavity is the most familiar and visible part of the vocal tract. Various structures of the oral cavity have roles in both the act of speaking as well as mastication and deglutition. These structures include the tongue, teeth, alveolar ridge, hard palate, velum, anterior faucial pillars, posterior faucial pillars, and palatine tonsils. The hard palate plays a significant role in allowing appropriate mastication of food. The alveolar ridge of the hard palate is also important for appropriate articulation as the tongue contacts the ridge during the production of alveolar phonemes. The buccal cavities are the spaces between the lateral dental arches, the posterior teeth, and the flesh of the cheeks on both sides of the oral cavity; they are important for appropriate mastication and oral resonance. The nasal cavity extends anteriorly from the nares to the nasal choanae posteriorly. Air and the sound of phonation are passed through the nasal cavity to produce nasal phonemes. The pharynx is a muscular tube that is posterior to the nasal and oral cavity. It is divided into three primary regions: nasopharynx, oropharynx, and laryngopharynx. The tongue is composed primarily of muscle and plays a significant role in speech, mastication, and swallowing. It is composed of intrinsic and extrinsic muscles. The intrinsic muscles of the tongue comprise the mass of the tongue. They originate and terminate within the tongue and are responsible for changing the shape of the tongue and the execution of fine motor movements. These muscles include the superior and inferior longitudinal muscle, the vertical muscle, and the transverse muscle. The extrinsic muscles of the tongue originate elsewhere and insert into the tongue. These muscles are responsible for gross movement of the tongue. These muscles include the genioglossus, hyoglossus, styloglossus, and palatoglossus. The muscles of mastication are important for the movement of the mandible. The mandible can be elevated, depressed, protruded, retracted, and lateralized for the purposes of grinding food

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during mastication. These muscles include the masseter, temporalis, medial pterygoid, lateral pterygoid, digastricus, mylohyoid, and geniohyoid. The muscles of the velum either elevate or depress the velum. The function of the velum is to elevate and seal off the nasal cavity from the pharynx during deglutition and nonnasal speech sounds. Elevators of the velum include the levator veli palatini and the musculus uvulae with assistance from the tensor veli palatini whose primary role is dilation of the eustachian tube. Depressors of the velum include the palatoglossus and the palatopharyngeus. The pharynx is important for various functions, such as resonance during speech, swallowing, and respiration. It is the link between the oral cavity and esophagus, as well as between the nasal and oral cavities. The muscles of the pharynx are divided into the constrictors and the longitudinal muscles. The pharyngeal constrictor muscles constitute the walls of the pharynx and are responsible for pharyngeal constriction, particularly during a swallow. These muscles include the superior pharyngeal constrictor, the middle pharyngeal constrictor, and the inferior pharyngeal constrictor. The inferior pharyngeal constrictor is divided into the thyropharyngeal muscle and the cricopharyngeal muscle. The longitudinal muscles of the pharynx elevate the pharynx during deglutition and include the palatopharyngeus, salpingopharyngeus, and stylopharyngeus.

➤ References Becking, A. G. (2000). Distractieosteogenese van de mandibula als behandeling bij 2 kinderen met hogeluchtwegobstructie bij micrognathie, Nederlands tijdschrift voor geneeskunde, 144(44), 2111–2115. Cooper-Brown, L., Copeland, S., Dailey, S, Downey, D., Peterson, M.C., Stimson, C., & Van Dyke, D. C. (2008). Feeding and swallowing dysfunction in genetic syndromes. Developmental Disabilities Research Reviews, 14(2), 147–157. Darwin, C. (1998). The expression of the emotions in man and animals (3rd ed., Ed. P. Ekman). Harper Collins; Oxford University Press [Google Scholar]. Ekman, P. (2003). Emotions revealed. Henry Holt and Co. Ekman, P., & Friesen, W. (1978). Facial action coding system: A technique for the measurement of facial movement. Consulting Psychologists Press. Fernandez, A., & Morris, R. (2007). Sexual selection and trichromatic color vision in primates: Statistical support for the preexisting-bias hypothesis. The American Naturalist, 170(1), 10–20.

Hager, J. C. (1982). Asymmetries in facial expressions. In P. Ekman (Ed.), Emotion in the human face (2nd ed., pp. 318–352). Cambridge University Press. Parent, A. (2005). Duchenne de Boulogne: A pioneer in neurology and medical photography. Canadian Journal of Neurological Sciences, 32(3), 369–377. Pope, L., & Smith, C. (1994). On the distinct meanings of smiles and frowns. Cognition & Emotion, 8, 65–72. Russel, J.A. (1994). Is there a universal recognition of emotion from facial expression? A review of the cross-cultural studies. Psychological Bulletin, 115(1), 102-141. Shkoukani, M. A., Lawrence, L. A., Liebertz, D. J., & Svider, P. F. (2014). Cleft palate: A clinical review. Birth Defects Research: Part C, Embryo Today, 102(4), 333–342. Strack, F., Martin, L. L., & Stepper, S. (1988). Inhibiting and facilitating conditions of the human smile: A nonobtrusive test of the facial feedback hypothesis. Journal of Personality and Social Psychology, 54(5), 768–777.

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➤ Learning Objectives Upon completion of this chapter, students will be able to: n

Identify the function of relevant anatomical structures used as mobile and immobile articulators for speech.

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Describe how associated musculature lends movement to mobile articulators such as the tongue, lips, and velum.

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Understand mobile articulators move to contact or approximate immobile articulators for speech.

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Describe the role of the tongue in oral resonance.

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Understand resonance, resonant frequency, and the source-filter theory of vowel production.

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Identity differences in the production of consonants, vowels, and diphthongs.

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Explain the role of the velum in appropriate nasality of phonemes as well as hypernasality and hyponasality.

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➤ Introduction to Articulation and Resonance The understanding of the acts of articulation and resonance are central to the professional work of most speech-language pathologists. The structures of the vocal tract complete these complex actions quickly, fluidly, and usually with very little error. For the most part, most individuals complete these tasks in a highly automatic and overlearned fashion, rarely even considering the complex symphony of movements that allows them to accomplish normal articulation and resonance. However, problems do occur when normal articulation and/or resonation fail to arise in certain children, structural abnormalities interfere with these abilities, or disease or other etiologies negatively impact these important functions. When this occurs, it is the work of the speech-language pathologist to provide therapy for these difficulties. However, prior to understanding disorders of articulation and resonance, or therapy for these disorders, the student of speech-language pathology must first understand the physical processes of articulation and resonance.

➤ Physiology of Articulation and Resonance Articulation is the act of using the structures of the vocal tract to shape phonemes for speech production. The structures of the vocal tract involved in articulation of speech that move for production of speech are the mobile articulators. These include the lips, the mandible, the tongue, and the velum. The mobile articulators create different locations and degrees of constriction in the vocal tract to produce different phonemes. The vocal tract structures upon which the mobile articulators act for speech but which are themselves incapable of movement are the immobile articulators. These include the teeth, the alveolar ridge, and the hard palate. Resonance is how the human vocal tract reinforces and projects some frequencies of the voice (phonation), while inhibiting other frequencies. Articulation and resonance are intertwined and interrelated. It is through changing the resonance of the oral cavity by varying tongue position that different vowels are produced. It is by varying the degree of nasality in speech by varying the position of the velum that nasal and nonnasal phonemes are produced. If one’s resonance is abnormal, then appropriate articulation of speech sounds may also be negatively impacted. The student of speech-language pathology needs to fully appreciate the intricate processes of articulation and resonance in the production of speech. Speech is a highly coordinated and dancelike movement of mobile articulators against immobile articulators timed strictly with the respiratory process and rapid adduction/abduction of the vocal folds for the accurate production of voiced and voiceless phonemes. Next time you are speaking, try to pay conscious attention to the movement, range of motion, and speed of your articulators. When speaking, we average around four to five syllables per second (Jacewicz et al., 2009). If you break that statistic down from syllables per second into phonemes per second, you get a rate of around 10 phonemes per second produced during spontaneous speech. If you then begin to consider how many muscles across the body are simultaneously contracting to produce each phoneme at this speed, one begins to comprehend the true complexity of speech production. Furthermore, consider how rarely most of us make articulatory errors. It is a remarkable feat of the human motor system.

Role of the Lips in Articulation The lips are highly associated with many muscles of the face, which lends the mouth its agility and range of motion for the purposes of facial expression and eating and drinking. The lips are also important 266

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articulators for the production of speech and allow us to produce many specific phonemes. The lips are formed by a layer of transparent epithelial tissue, which reveals the red-colored vascular tissue beneath. Deep to this layer is the muscle of the lips, primarily the orbicularis oris. External features of the lips include the philtrum, philtral ridges, cupid’s bow, commissure, and vermilion zone (Figure 7–1): n The

philtrum is the medial and vertical indentation that runs from the nasal septum to the upper lip. On either side of the philtrum are raised vertical columns, which are the philtral pillars.

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The philtral pillars meet the upper lip at two peaks in the upper lip that form a curvature of the lip known as cupid’s bow due to its resemblance to the shape of the bow carried by cupid.

n The

vermilion border of the lips is the boundary between the paler skin of the face and the pinker or scarlet (vermilion) colored skin of the lips. commissure of the lips is where the vermilion border of the lower lip meets the vermilion border of the upper lip. This is commonly known as the corner of the mouth.

During the articulation of speech, the lips act as mobile articulators. The lower lip, being attached to the mandible, which is also highly mobile, moves more often, faster, and with a greater range of motion than the upper lip. In certain diseases like Parkinson disease, it can be observed that the upper lip can lose almost all movement, but if the lower lip retains a functional degree of movement, the articulation of phonemes involving the lips may not be negatively affected. The orbicularis oris is the primary muscle of the lips and constitutes much of the mass of the lips. The orbicularis oris is involved in fine movement of the lips and has many muscles of the face that insert into the orbicularis oris from different angles to give the lips a greater range of motion in the direction of their origin. The role of the orbicularis oris in articulation is as follows: n

The upper and lower lips are compressed together for the buildup of oral pressure to be held then suddenly released for bilabial stop-plosive phonemes (/p/, /b/). This is done via contraction of the superior and inferior orbiculares oris.

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For labiodental phonemes, the lower lip is pressed into the upper teeth, and the expiratory airstream is directed between them for the production of labiodental phonemes (/f/, /v/). This compression of the lower lip into the upper teeth is accomplished largely via the orbicularis oris inferior.

FIGURE 7–1.  Anatomy of the lips. Reproduced with permission from Anatomage.

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The lips are rounded and protruded for the production of labial phonemes (/w/, /hw/) and some low-back vowels (Figure 7–2). The rounding of the lips for these phonemes is accomplished via contraction of the mentalis and the orbicularis oris.

Role of the Tongue in Articulation The tongue is by far the most active mobile articulator during speech and comes into play for the articulation of most phonemes. It is directly responsible for most consonants, all vowels, and all diphthongs. The mobility and range of motion of the tongue are further increased by its relationship with the mandible. The tongue rests on the floor of the oral cavity, which is slung between the two horizontal arches of the mandible. As the mandible can be considered the foundation on which the tongue resides, the additional mobility of the mandible gives the tongue a greater range of movement for the purposes of speech, mastication, and deglutition. If the muscles of the mandible are bilaterally and severely weakened, the mandible cannot be raised at all, the tongue will not be able to approximate the palate and teeth for articulation, and speech will be negatively impacted.

Role of the Muscles of the Tongue in Articulation The tongue is able to assume many articulatory positions, and each position employs a complex combination of lingual muscles to move and stabilize the tongue. The muscles of the tongue are divided into intrinsic and extrinsic muscles. Although there is not a strict division in function of articulation between the intrinsic and extrinsic muscles, the intrinsic muscles are highly involved in the fine movement of the tongue used during articulation while the extrinsic muscles are more involved in the gross movement of the tongue, stabilization of the tongue, and positioning of the tongue within the oral cavity. A combination of these muscles is responsible for the wide range of motion and the many types of motion of which the tongue is capable. For production of consonants, the action of the tongue is that of articulating with various structures in varying ways to produce places and degrees of constriction in the vocal tract for production of differ-

FIGURE 7–2.  Lip position for /w/ phoneme.

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ent consonants with or without phonation present. For the production of vowels, an open vocal tract position, one with relatively less constriction, is assumed; then by changing the position of the tongue, oral resonance is changed, producing different vowels.

Role of the Tongue in Consonant Production n

In the case of linguadental consonants, /θ/, /ð/, the tip of the tongue elevates to the upper incisors, while the lateral edges of the tongue seal off and direct airflow between the tongue tip and the upper frontal incisors (Figure 7–3).

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For alveolar consonants such as /t/, /d/, /s/, /z/, /ʃ/, /tʃ/, /dʒ/, the tip of the tongue is raised to either contact the alveolar ridge as in the production of alveolar stops or affricates (/t/, /d/, /tʃ/, /dʒ/) or approximate the alveolar ridge and direct expiratory airflow as in the case of alveolar fricatives /s/, /z/, and /ʃ/.

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For velar stop consonants, /k/, /g/, the posterior dorsum of the tongue is raised to approximate the posterior hard palate to create a momentary seal and then release expiratory pressure to create these stop-plosives.

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In the case of the liquid consonant /r/, the posterior dorsum of the tongue is raised to approximate the velum. For the liquid consonant /l/, the tip of the tongue contacts the alveolar ridge while the lateral edges of the tongue are relaxed.

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The tongue is not involved in bilabial, labiodental, and glottal phonemes (/p/, /b/, /m/, /f/, /v/, /h/).

The tongue is responsible for appropriate production of all vowel sounds: n

The position of the tongue in the oral cavity largely dictates resonance of the oral cavity and therefore the vowel that is produced. The tongue changes the vowels produced by the vocal tract by acting as a valve and changing the length and volume of the oral cavity. By changing

FIGURE 7–3.  Lingual position for “th” phonemes (/θ/, /ð/).

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these physical characteristics of the oral cavity, the tongue changes the frequencies of the phonatory signal (the voice) that are either suppressed or propagated by the oral cavity. These changes, the suppression or propagation of varying frequencies of the phonatory signal, produce varying vowels. n

Changes in resonant characteristics of the oral cavity produce the varying vowels.

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Before getting into detail about how changes in tongue position produce different vowels, it is important to understand more about resonance. More specifically than mentioned earlier, resonance is the process by which an air-filled cavity, or a container of air, inhibits certain sound frequencies while reinforcing other frequencies based on physical properties of the container, such as volume and length.

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Consider when you blow across the open-mouth soda bottle and the soda bottle emits a tone (Figure 7–4). What is happening is that the air-filled cavity of that soda bottle is resonating. When you blow across the mouth of the bottle, you are introducing into that bottle many different frequencies of sound all mixed into a white noise that is the hiss of your airstream cutting across the rim of the mouth of the bottle. Based on the length and volume of the bottle, it will produce one single loud tone in response to you blowing across the mouth of the bottle. This tone produced by the bottle is the frequency it selected out of all the frequencies in the white noise that it most strongly responds to and vibrates with. This frequency of sound is referred to as the container’s resonant frequency. So, when all those random frequencies of sound (i.e., the white noise made at the mouth of the bottle) enter the bottle, it will select out of that noise its resonant frequency to vibrate with, thereby propagating its resonant frequency while inhibiting the frequencies that it does not resonate to.

FIGURE 7–4.  Blow across the mouth of a bottle to demonstrate the resonant frequency of an air-filled container.

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Source-Filter Theory of Vowel Production In the previous example, the bottle is acting as a filter for the raw sound source that is the hiss of the airstream blown across the mouth of the bottle. The resulting output hum of the bottle is the resonatory frequency of the bottle dictated by the container’s volume and shape. Expiratory airflow provides the power to create the sound source by expelling air forcefully across the open mouth of the bottle.

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If we apply these ideas to the vocal tract (Figure 7–5), we are able to understand that expiratory airflow provides the power for phonation by driving the vocal folds during phonation.

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Phonation is the sound source for vowels.

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The cavities of the vocal tract are interconnected chambers (Figure 7–5), each with its own resonant characteristics that all together act as filters for that sound.

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Now if we consider that the tongue is the primary structure that changes the volume and length of the oral cavity, then we can begin to understand that the tongue is, in this way, responsible for changing the resonatory characteristics of the oral cavity.

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As the base of the tongue is also the anterior wall of the pharyngeal cavity (Figure 7–5), movement of the tongue also changes the length and volume of the pharyngeal cavity, which results in changing resonatory characteristics of the pharyngeal cavity as well as the oral cavity.

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The lips also play a role in increasing or decreasing length and volume of the oral cavity, thus changing resonatory characteristics of the oral cavity. Protruding and rounding the lips increases

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FIGURE 7–5.  Cavities of the vocal tract.

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length and volume of the oral cavity. Retraction of the lips decreases length and volume of the oral cavity. n

This process of cavities of the vocal tract suppressing (or filtering out) certain frequencies of the raw phonatory signal while propagating other frequencies to produce the varying spectrum of possible vowels is known as the source-filter theory of vowel production.

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The raw phonatory signal, the unfiltered sound of the human voice, is a buzzing sound that sounds nothing like the human voice we are familiar with. However, when that raw spectrum of frequencies produced by the vocal folds is then projected through the vocal tract, where the volume and length of each cavity of the vocal tract suppresses some frequencies of the voice signal while allowing other frequencies to pass unimpeded, it creates what we understand as the human voice.

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Within the stepwise explanation for source-filter theory of vowel production presented earlier, one learns that it is primarily through the action of the tongue that the resonatory characteristics of the oral and pharyngeal cavities are varied to produce different vowels. Figure 7–6 depicts differing tongue positions used to produce four different vowels.

Vowel Quadrilateral So now that we understand why different positions of the tongue in the oral cavity will produce different phonemes, let us examine those varying tongue positions and resulting vowels: n

Vowels are, in fact, categorized by the position of the tongue in the oral cavity during production. Tongue positions during the production of vowels are categorized by two

FIGURE 7–6.  Tongue positions during vowel production.

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parameters: vertical (high, mid, and low) and sagittal (front, central, and back) (Figures 7–6 and 7–7). n

For example, the vowel /u/ is categorized as a high-back vowel (Figure 7–7). For the production of this vowel, the mass of the tongue would be positioned superiorly and posteriorly in the oral cavity, whereas the vowel /i/, which is a high-front vowel (Figure 7–7), requires a superior and anterior tongue position.

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High-front vowels include /i/, /ɪ/ (Figure 7–7). High-back vowels include /u/, /ʊ/ (Figure 7–7).

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Mid-front vowels include /e/, /ɛ/ (Figure 7–7). Mid-central vowels include /ə/, /ɝ/, /ɚ/, /ʌ/ (Figure 7–7). Mid-back vowels include /o/, /ɔ/ (Figure 7–7).

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Low-front vowels include /æ/ (Figure 7–7). Low-central vowels include /a/ (Figure 7–7). Low-back vowels include /ɑ/ (Figure 7–7).

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When we graph the relative position of the tongue during production of all the vowels, it produces a common image known as the vowel quadrilateral (Figure 7–7).

The Role of the Tongue in Diphthongs A diphthong is a vowel-like consonant that is produced with an open vocal tract and is characterized by a transition from one tongue position to another that produces a transition from one vowel sound to another within a single syllable. This is opposed to a monophthong that is a vowel sound with a single constant perceived quality due to an unchanging single tongue position: As the tongue is the primary articulator of diphthongs, the quick movement of the tongue from one position to a second position within a syllable is required for the production of a diphthong. Physiology of Articulation and Resonance

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FIGURE 7–7.  Vowel quadrilateral.

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The protrusion and retraction of the lips as well as the elevation and depression of the mandible during articulation to assist in the altering of resonatory characteristics of the vocal tract also contribute to the appropriate production of diphthongs.

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The phonetic symbols for diphthongs are the two vowels they are composed of.

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An example of a diphthong is the vowel in the word “cow” phonetically spelled /kaʊ/. When producing this diphthong, the initial oral position for the /a/ phoneme is with the lips retracted and the tongue positioned for the low-central vowel /a/. The lips then protrude and round while the tongue moves to a second position for production of the high-back vowel of /ʊ/.

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The eight diphthongs in English are (Table 7–1) /eɪ/, /aɪ/, /əʊ/, /aʊ/, /ɔɪ/, /ɪə/, /eə/, and /ʊə/.

TABLE 7–1.

The Eight Dipthongs in English

Dipthongs

Word

Phonetic Transcription

e͡ ɪ

say

/se͡ ɪ/

a͡ ɪ

live

/la͡ ɪv/

o͡ ʊ

dome

/do͡ ʊm/

a͡ ʊ

cow

/ka͡ ʊ/

ɔ͡ɪ

coin

/kɔ͡ɪn/

͡ɪə

fear

/f ͡ɪɚ/

e͡ ə

tear

/te͡ ɚ/

ʊ͡ə

sure

/ʃʊ͡ɚ/

Acquired Lingual Weakness Weakness of the tongue is perhaps most often acquired through damage to the nervous system by stroke or trauma. Acquired weakness of the tongue can be unilateral (one side affected) or bilateral (both sides affected), spastic or flaccid, and can negatively impact speech and swallowing. If weakness of the tongue negatively affects speech, it is dysarthria. If it negatively affects mastication or swallowing, it is dysphagia. Most often with a unilateral (one sided) weakness of the tongue, the range and force of lingual movement may be reduced, and articulation may be negatively impacted, but overall intelligibility of the individual’s speech is mostly preserved. This is because the intact side of the tongue is able to drag the weakened side of the tongue into, more or less, appropriate articulatory positions for speech. Unilateral weakness of the tongue is recognized during protrusion of the tongue as the tongue will deviate to one side (Figure 7–8). With unilateral weakness, the tongue will deviate toward the weakened side on protrusion. Usually, atrophy of the muscles of the tongue on the weakened side can be recognized by a shrunken, wrinkled appearance. Certainly, some articulatory slowness and/or mild distortions of phonemes are to be expected.

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FIGURE 7–8.  Tongue deviating to left indicating left unilateral lingual weakness.

Role of the Teeth in Articulation The teeth act as immobile articulators during articulation of speech. Primarily when we speak of the teeth as immobile articulators, we are speaking of the upper anterior teeth: n

The lower lip elevates to contact or closely approximate the upper central and lateral incisors for the production of the labiodental consonants (Figure 7–9).

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The labiodental consonants are /f/, /v/.

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The apex of the tongue elevates to contact or closely approximate the upper central and lateral incisors for the production of the linguadental phonemes.

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The linguadental consonants are /θ/, /ð/.

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With moderate and severe bilateral weakness of the tongue, there is no intact side to pull the weakened side along. Bilateral weakness of the tongue can be recognized by reduced capability of tongue protrusion and by a bilateral shrunken and wrinkled appearance of both sides of the tongue, reflecting atrophy on both sides of the tongue. Force and range of movement of the tongue can be more substantially reduced with bilateral weakness of the tongue than unilateral weakness. The negative impact on speech of bilateral weakness can be profound if the tongue has too little capability for movement. In the scenario of weakness of the tongue, it is the role of the speech-language pathologist to teach compensatory strategies for speech and swallowing while working to increase the strength of the tongue.

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 7–9.  Oral position of /f/, /v/.

the dental arches that inhibit functional approximation of the lips and tongue to the upper incisors will negatively impact articulation.

Role of the Mandible in Articulation As mentioned previously, as the mandible supports the lower lip and the tongue, it is highly important for appropriate articulation. If you place your hand on your chin while you speak, you will feel the motion of the mandible as it assists in articulation. During articulation, the motion of the mandible is primarily in the vertical dimension (up and down). However, it is capable of lateralization and protrusion and retraction, which are used less during speech than in the process of mastication. The mandible is important for assisting in the elevation of the lower lip to the upper lip for the production of bilabial phonemes and for elevation of the lower lip to the upper teeth for the production of labiodental phonemes. As the mandible cradles the tongue on the floor of the oral cavity, it is essential for elevating the tongue for appropriate approximation of the tongue to the teeth, alveolar ridge, and palate for production of consonants. However, the mandible also works to lower and elevate the tongue as it changes position for the production of vowels. In this way, the mandible assists the tongue in altering the length and volume of the oral cavity for the production of different vowels. You can demonstrate this to yourself if you rest your hand under your chin and verbalize the vowels in order from high-front to low-back and feel the increasing depression of the mandible as it lowers to increase volume of the oral cavity. Even with no consonants being produced, you will feel significant movement of the mandible. You can demonstrate the importance of the movement of the mandible in articulation if you hold your mouth wide open, keeping your mandible still and as low as possible, and attempt to speak as normal. You will notice that although your tongue and lower lip move with the words you want to say, they cannot approximate the immobile articulators such as the upper lip, upper teeth, and alveolar ridge; therefore, your articulation of speech is seriously compromised. In this situation, you will probably even struggle to produce appropriate vowels. However, the articulatory system is able to adapt itself to compensate for less extreme negative changes in physiology and movement capability of the mobile articulators for the purpose of intelligible speech production. You will notice that if you depress and restrain your mandible just slightly lower than normal, not allowing it to elevate, and try to speak, 276

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your articulatory system is probably able to functionally adapt, allowing you to produce perhaps odd sounding but still intelligible speech. This slight degree of restraint you have put on the parameter of mandibular movement is compensated for by the motor system automatically altering other parameters of articulatory movement such as increasing the elevation of the lower lip to produce labiodental phonemes, increasing the depression of the upper lip to be able to meet the lower lip for production of bilabials, increasing elevation of the tongue to be able to approximate the upper teeth for linguadentals, and elevating the tongue to the different parts of the maxillae to produce consonant phonemes that involve the tongue as well as to change resonant characteristics of the oral cavity for vowels. The mobility of the temporomandibular joint (Figure 7–10) allows for this range of movement: n

The temporomandibular joints, left and right, are synovial joints, which means that the articulating surfaces of the condylar process of the mandible and the mandibular fossa of the temporal bone are characterized by smooth gliding cartilaginous surfaces lubricated between by a viscous fluid, known as synovial fluid, which allows for a great range of movement.

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The temporomandibular joints are characterized by an upper synovial cavity or compartment and a lower synovial cavity compartment divided by an articular disc:

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The upper and lower synovial cavities of the temporomandibular joint each have a synovial cavity with a membrane that produces synovial fluid to lubricate the joint. The articular disc is composed of dense nonvascular and fibrous tissue. The particular anatomy of this joint effectively constitutes a double joint, with the upper synovial cavity allowing for retraction, protrusion, and lateralization of the mandible and the lower synovial cavity allowing for elevation, depression, and rotational movement. The two cavities of this joint are used simultaneously to produce the wide range of mandibular movement. Physiology of Articulation and Resonance

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FIGURE 7–10.  Temporomandibular joint. Reproduced with permission from Anatomage. 277

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Mandibular Weakness Weakness of the mandible, or specifically, weakness of the muscles responsible for moving the mandible, can be acquired via any number of etiologies, such as stroke, trauma, and disease. As the mandible holds the tongue and the lower lip protrudes off it anteriorly, one can readily perceive how negatively speech and mastication could be affected if movement of the mandible is reduced. If a mandibular weakness negatively affects speech, it is dysarthria; if it negatively affects mastication, it is dysphagia. Unilateral weakness of the mandible is recognized during an exam as deviation of the mandible away from midline on opening of the mouth (depression of the mandible). In the case of a unilateral weakness, the mandible, upon depression, will hinge and deviate toward the weakened side (Figure 7–11). However, as was the case with unilateral weakness of the tongue, in the case of unilateral mandibular weakness, the intact side is still able to compensate and position the mandible appropriately for speech. However, mastication involves far more mandibular movement than speech, and unilateral weakness can cause someone to masticate using only the intact side of the mandible. Bilateral weakness of the muscles of the mandible can present a far more dire situation for speech and mastication. With a severe bilateral weakness of the mandible, the mandible is unable to lift the tongue to approximate any other structures for articulation of consonants, and also vowel production is severely reduced by a lack of appropriate oral positioning to create normal oral resonance. The speech of the affected individual is usually wholly unintelligible to the unfamiliar listener in this scenario, though the speaker may be able to manually position their mandible for speech by elevating it with a hand. Mastication in this scenario becomes impossible, and usually the individual will be placed on a diet of pureed food that they can swallow without mastication, while the speech-language pathologist works to strengthen the muscles of the mandible.

FIGURE 7–11.  Mandible deviating to left upon depression indicating left unilateral mandibular weakness.

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n

Muscles that act as mandibular elevators are the masseter, anterior fibers of the temporalis, and medial pterygoid.

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Muscles that act as mandibular depressors are the anterior belly of the digastricus, mylohyoid, geniohyoid, and platysma.

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Muscles that act to protrude the mandible are the lateral pterygoid and, to a lesser degree, the medial pterygoid.

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Muscles that act to retract the mandible include the posterior fibers of the temporalis.

The cheeks are lateral to and continuous with the lips, forming the lower sides of the face. The cheeks are composed of muscle tissue as well as glandular, areolar, vascular, and nervous tissue. Much of the mass of the cheeks is the buccinator muscle, which is the primary muscle of the cheek and is important for keeping tension in the cheeks during speech as well as during mastication. Other muscles that play a role in articulation, mastication, and facial expression, such as the risorius and zygomatic major, are also located within the cheeks. The most external layer of the cheeks is the skin on the surface of your face. Inside the oral cavity, the superficial layer of the cheeks is the mucous membrane that is continuous with the oral cavity. Muscles of the cheeks must be kept tense for appropriate buildup of intraoral pressure for the production of consonants such as bilabial stops and labiodental fricatives. Weakened or hypotonic muscles of the cheeks will result in the redirection of intraoral pressure away from the lips where the pressure needs to be directed for release, and into the buccal cavities causing the cheeks to inflate and quiet or alter the production of the affected phonemes. This particular articulatory difficulty is often observed in small children with syndromes that can create low muscle tone, such as Down syndrome. As the cheeks constitute the lateral walls of the oral cavity, they are necessary for maintaining normal oral resonance.

Role of Velum in Articulation and Resonance The nasal cavity is the space created behind the nostrils (nares) with the maxillae and palatine bones constituting the inferior and lateral boundaries, the nasal bones constituting the anterior superior boundary, and the ethmoid constituting the posterior superior boundary. Medially, the nasal cavity is divided into right and left halves by the nasal septum. The nasal cavity opens posteriorly into the nasopharynx. The velum, also known as the soft palate, is the flap of muscular tissue that hangs off the back of the hard palate where the posterior nasal cavity opens into the pharynx. The velum acts as a valve structure between the nasal cavity and the oropharynx by depressing to open the nasal cavity to the pharynx, or elevating to close off the nasal cavity (Figure 7–12A and B). In addition to the depression and elevation of the velum, the lateral walls of the nasopharynx retract with the velum to assist in sealing off the nasal cavity. The posterior pharyngeal wall also is pulled anteriorly to meet the elevating velum during closure. This action is accomplished via the superior pharyngeal constrictor muscle. The valve created by these actions and structures is known as the velopharyngeal port. The actions of the velum and of the velopharyngeal port during speech change the resonatory characteristics of the vocal tract in ways that produce different phonemes:

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A

B FIGURE 7–12.  A. Velum depressed and lips closed allowing air and voice to pass through nasal cavity for the production of nasal phonemes. B. Velum elevated and sealing off nasal cavity directing airflow and voice oral cavity for nonnasal phonemes.

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If the velum is depressed during expiration air can pass from the pharynx and be expired through the nasal cavity (Figure 7–12A). During phonation, a depressed velum allows for the expiratory airstream as well as more phonatory frequencies to pass through the nasal cavity. This combined with a sealed oral cavity increases the resonant quality of nasality of the vocal tract for the production of the three nasal phonemes (/m/, /n/, /ŋ/).

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The location at which the oral cavity is sealed during production of the nasal phonemes will determine which nasal phoneme is produced. By changing the location of the seal of the oral cavity, one alters the length and volume of the oral cavity, which changes the resonatory characteristics of the vocal tract. This allows for the production of the three different nasal phonemes.

n

The /m/ phoneme requires the oral cavity to be sealed at the lips (Figure 7–12A). The /n/ phoneme requires the oral cavity to be sealed at the alveolar ridge by the tongue. The /ŋ/ requires the oral cavity to be sealed at the posterior hard palate by the posterior body of the tongue.

n

The oral cavity length and volume are increased as the lips create the anterior-most seal at the mouth for the /m/ phoneme. The length and volume of the oral cavity then reduce as the tongue moves more posteriorly to the alveolar position for the production of /n/, then even more posterior to the velar position for /ŋ/.

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Muscles responsible for depression of the velum are the palatoglossus and palatopharyngeus.

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When elevated, the velum assists in closing the velopharyngeal port. The velum is elevated and retracted during the articulation of nonnasal phonemes and during deglutition (Figure 7–12B). During phonation, a closed velopharyngeal port directs the expiratory airstream and more phonatory frequencies through the oral cavity than through the nasal cavity. This decreases the nasal resonant quality of the vocal tract for the production of nonnasal phonemes.

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The oral stop consonants (plosives), such as /t/, /d/, /p/, /b/, /k/, and /g/, all require the velopharyngeal port to be highly sealed. This allows for the buildup of the necessary high oral pressures that these phonemes require for the release of the airstream producing their initial explosive sound burst.

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The muscles responsible for elevation of the velum are the levator veli palatini, tensor veli palatini, and musculus uvulae.

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Although the velum is often discussed simply as being depressed or elevated, the velopharyngeal port is a sphincterlike structure that can create any degree of opening or sealing off of the nasal cavity. The velum is not a simple binary structure that is either always fully open or always fully closed.

n

For instance, some vowels, such as the low-back vowels, require a degree of velopharyngeal port opening, though not as much as is required for nasal phonemes (Fuller et al., 2012). Furthermore, through the process of assimilation, nasal phonemes can confer some degree of their increased nasal resonance to nonnasal phonemes such as vowels (Rochet & Rochet, 1999). Also, the habitual degree of elevation or depression of the velum during speech varies between dialects and geographic areas, meaning that the degree of what is considered normal nasality varies geographically and culturally (Awan et al., 2015).

n

When there is a lack of effective seal of the closed velopharyngeal port, too much nasality is produced on nonnasal phonemes creating the resonatory quality known as hypernasality. When the nasal cavity is sealed off from the pharynx too much, there is too little nasality in nasal phonemes, and this results in the resonant quality known as hyponasality.

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A lack of effective seal of the velopharyngeal port is usually categorized as velopharyngeal incompetence or velopharyngeal insufficiency. Velopharyngeal insufficiency is a lack of appropriate velopharyngeal seal due to abnormal anatomical structure such as a short velum that is unable to close the velopharyngeal port (Figure 7–13A). Cleft palate also compromises the velopharyngeal port and creates velopharyngeal insufficiency. Velopharyngeal incompetence refers to a lack of appropriate velopharyngeal seal caused by an inability to move anatomical structures normally, such as muscle weakness (Figure 7–13B). Both of these conditions can be referred to as VPI. Resonance disorders associated with the velum can be caused by velopharyngeal insufficiency or velopharyngeal incompetence or some combination of the two.

n

Examples of conditions that can create hyponasal resonance: n

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Hyponasality is most often caused by anatomical obstruction within the nasal cavity. This can be due to swelling, such as from surgery within or around the nasal cavity, from a common cold, or from any number of other sources. Velopharyngeal mislearning may occur in which a child has a functional and appropriate velum but has simply learned or developed speech in a way that is not employing proper velopharyngeal function for normal nasality.

The following are examples of conditions that can create hypernasal resonance: n

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Cleft palate:  Clefting of the hard palate and/or velum can create inappropriate openings within those structures that allow expiratory air and phonatory signal to be directed into the nasal cavity inappropriately, creating hypernasality. Genetic syndromes:  Chromosomal disorders can produce craniofacial abnormalities with anatomical differences that make appropriate velopharyngeal closure difficult or impossible. Some examples of these genetic syndromes include Treacher Collins, Kabuki, CHARGE, Pierre Robin sequence, and Down syndrome. Neurogenic disorders:  Acquired neurogenic conditions such as stroke or traumatic brain injury can create weakness of the velum, as can degenerative diseases of the nervous system such as multiple sclerosis or amyotrophic lateral sclerosis. This weakness of the velum can reduce appropriate velopharyngeal closure, creating hypernasality. Acquired anatomical abnormalities:  Surgery at or around the velopharyngeal port such as to the nasopharynx in the form of removal of the adenoids can at times reduce appropriate velopharyngeal seal and increase the nasality of the speaker.

Role of the Pharynx in Articulation Although the pharynx plays a minimal role in articulation of phonemes (Fuller et al., 2012), it makes its primary contributions within the realms of swallowing and resonance. The pharynx is an important resonator of voice during speech and, following the source-filter theory described earlier, is one of the cavities of the vocal tract that acts as a filter for phonation.

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A

B FIGURE 7–13. A. Velopharyngeal insufficiency due to shortened velum allowing air and voice to escape through nasal cavity during nonnasal phonemes. B. Velopharyngeal incompetence caused by weakness of velum allowing air and voice to escape through nasal cavity during nonnasal phonemes.

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➤ Chapter Summary The acts of articulation and resonance are central to the professional work of most speech-language pathologists. Articulation is the act of using the structures of the vocal tract to shape phonemes for speech production. The structures of the vocal tract involved in articulation of speech that are movable are the mobile articulators. These include the lips, mandible, tongue, and velum. The vocal tract structures upon which the mobile articulators act for speech but which are themselves incapable of movement are the immobile articulators. These include the teeth, alveolar ridge, and hard palate. Resonance is how the human vocal tract reinforces and projects some frequencies of the voice, while inhibiting others, during phonation. Articulation of speech and resonance work together for the production of appropriate phonemes. The lips are important articulators for the production of speech and allow the production of many specific phonemes. The orbicularis oris is the major muscle of the lips that gives the lips a large range of motion to help produce various phonemes during speech. The tongue is the most active mobile articulator during speech and is directly responsible for most consonants, all vowels, and all diphthongs. For production of consonants, the action of the tongue is that of articulating with varying structures in varying ways to produce different consonants with or without phonation present. For the production of vowels, an open vocal tract position with minimal constriction is assumed, and by changing the position of the tongue, oral resonance is changed, producing different vowels. Vowels are categorized by the position of the tongue in the oral cavity during production. Tongue positions during the production of vowels are categorized by two parameters: vertical (high, mid, and low) and sagittal (front, central, and back). The source-filter theory of vowel production explains how the cavities of the vocal tract filter the raw phonatory signal that is the sound source while propagating other frequencies of phonation to produce the spectrum of vowels. A diphthong is a vowel-like consonant that is produced with an open vocal tract and is characterized by a transition from one tongue position to another that produces a transition from one vowel sound to another within a single syllable. The tongue, lips, and mandible each play a role in the production of diphthongs. Sometimes an injury or condition can lead to weakness of the tongue. Acquired weakness of the tongue can be unilateral or bilateral, spastic or flaccid, and can negatively affect speech and swallowing. If weakness of the tongue negatively affects speech, it is dysarthria. If it negatively impacts mastication or swallowing, it is dysphagia. Often with a unilateral weakness of the tongue, lingual movement may be reduced which may negatively impact articulation; however, the individual’s overall speech intelligibility is mostly preserved because the intact side of the tongue is able to compensate for the weaker side. Bilateral weakness of the tongue has a far more negative impact on speech. The teeth act as immobile articulators in speech. Appropriate occlusion of the upper and lower dental arches is important for normal articulation, as is the presence and appropriate positioning of the incisors in the dental arch, as forms of malocclusion of the dental arches that inhibit functional approximation of the lips and tongue to the upper incisors will have a negative impact on articulation. The mandible acts as support for the lower lip and the tongue and, as such, is highly important for appropriate articulation. The mandible assists in the elevation of the lower lip to the upper

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➤ References Awan, S., Bressman, T., Puburka, B., Roy, N., Sharp, H., & Watts, C. (2015). Dialectical effects of nasalance: Multicenter, cross-continental study. Journal of Speech, Language, and Hearing, 58(1), 69–77. Fuller, D., Pimentel, J., & Peregoy, B. (2012). Applied anatomy and physiology for speech-language pathology and audiology. Lippincott Williams & Wilkins.

Jacewicz, E., Fox, R., O’Neill, C., & Salmons, J. (2009). Articulation rate across dialect, age, and gender. Language Variation and Change, 21(2), 233–256. Rochet, A., & Rochet, B. (1999). Patterns of assimilation nasality in English as a function of vowel height. In J. J. Ohala, Y. Hasegawa, M. Ohala, D. Granville, & A. C. Bailey (Eds.), 14th International Congress of Phonetic Sciences (ICPhS-14) (pp. 699–702).

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lip for the production of bilabial phonemes and for elevation of the lower lip to the upper teeth for the production of labiodental phonemes. It also cradles the tongue on the floor of the oral cavity and is essential for elevating the tongue for appropriate approximation of the tongue to the teeth, alveolar ridge, and palate for production of various consonants. Additionally, the mandible works to both lower and elevate the tongue as it changes position for the production of vowels. The cheeks constitute the lateral walls of the oral cavity and are appropriate for maintaining normal oral resonance. Muscles of the cheeks, the buccinators, must be kept tense for appropriate buildup of intraoral pressure for the production of consonants such as bilabial stops and labiodental fricatives. The velum is the flap of muscular tissue that hangs off the back of the hard palate where the posterior nasal cavity opens into the pharynx. The velum lowers to open the nasal cavity to the pharynx, and it rises to seal it off. These actions, along with the posterior pharyngeal wall moving anteriorly to meet the elevating velum during closure, create the velopharyngeal port. These actions change the resonatory characteristics in the vocal tract to produce different phonemes during speech output. Velopharyngeal insufficiency is a lack of appropriate velopharyngeal seal due to abnormal anatomical structure. Velopharyngeal incompetence refers to a lack of appropriate velopharyngeal seal caused by an inability to move anatomical structures normally, such as muscle weakness. Too much nasality, also known as hypernasality, is caused by the lack of an effective seal of the closed velopharyngeal port. Too little nasality, or hyponasality, occurs when the nasal cavity is sealed off from the pharynx too much. The pharynx plays a minimal role in articulation and mainly contributes to swallowing and resonance; it is an important resonator of voice during speech and is one of the cavities of the vocal tract that acts as a filter for phonation.

8 Physiology of Swallowing

➤ Learning Objectives Upon completion of this chapter, students will be able to: n

Describe the functions of the structures of the oral cavity, pharynx, larynx, and esophagus for mastication and deglutition.

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Describe the four stages of mastication and deglutition.

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Understand examples of dysphagias at each stage.

➤ Introduction to Swallowing Speech-language pathologists working in clinical settings constantly work with their patients to improve patients’ ability to take food by mouth and thereby maintain or improve their nutritional status. It is also paramount for the speech-language pathologist to make appropriate clinical decisions regarding those with disordered swallowing to minimize the patients’ risk of food falling into the open airway, reaching the lungs, and possibly causing aspiration pneumonia. Indeed, the treatment of dysphagia, mastication, and swallowing disorders is most often the highest priority of the speech-language pathologist. But prior to understanding disorders of mastication and deglutition, the speech-language pathology student must understand the basic processes of normal and unimpaired mastication and deglutition.

➤ Process of Mastication and Deglutition The swallowing process, though highly automatic for most individuals, is a complex process involving motor and sensory events of the structures of the oral cavity, pharynx, larynx, and esophagus (Figure 8–1). The purpose of mastication (chewing) is to prepare food into a ready-to-swallow mass known as a bolus. 287

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FIGURE 8–1.  Bolus passing from oral through pharyngeal stage. Reproduced with permission from Anatomage.

The neural control of the process of mastication originates in the brainstem at an area known as the masticatory central pattern generator (Lund & Kolta, 2006; Morquette et al., 2012). Central pattern generators are specific neural structures that, when activated, produce rhythmic movements such as mastication and walking. Mastication in humans and all mammals involves striated muscles operating under volitional control, though it is a highly automated process that we can interrupt or change at will (Jean, 2001). The purpose of deglutition, also known as the swallow, is to propel the bolus from the oral cavity ultimately into the stomach for digestion. The motor plan for the process of deglutition, known as the pharyngeal swallow, is more reflexive than voluntary and originates in the swallowing central pattern generator. The swallowing central pattern generator is responsible for the coordinated sequential movements of the pharyngeal swallow and is located in the medulla of the brainstem (Jean, 2001). Although the pharyngeal swallow itself is involuntary, we volitionally choose when to initiate this reflex as we transition food posteriorly in our mouth, and we can interrupt the pharyngeal swallow to some degree. The pharyngeal swallow ensures efficient transportation of liquid and solid boluses through the pharynx and safely over the airway into the esophagus. If any foreign material such as saliva, bolus material, or body secretion enters the airway, it is categorized according to how deeply it passes into the airway. Aspiration is when foreign material passes into the airway below the true vocal folds. Penetration is when foreign material passes into the airway but does not pass below the true vocal folds. 288

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The process of mastication and deglutition occurs in four stages. The stages of this process follow the bolus through the body as it is consumed: 1. Oral preparatory stage:  Food is placed in the mouth and is manipulated, masticated, and readied into a bolus. 2. Oral stage:  Mastication stops, and the tongue propels the bolus posteriorly toward the pharynx, which triggers the pharyngeal swallow (Figure 8–1A). 3. Pharyngeal stage:  This stage begins as the pharyngeal swallow is triggered and the bolus moves into and through the pharynx (Figure 8–1B, 8–1C). 4. Esophageal phase:  This phase begins once the bolus enters the esophagus and is carried through the esophagus to the stomach. These four stages are not static and are readily adapted to meet the needs demanded by the type, volume, and consistency of the food being masticated and swallowed (Kahrilas et al., 1991; Kahrilas & Logemann, 1993; Kahrilas et al., 1996). Therefore, there is a range of normalcy within the process of mastication and deglutition. Any change that decreases the function of mastication and deglutition outside of the range of normal to a degree of impairment is termed dysphagia.

Oral Preparatory Stage Described The primary function of the oral preparatory stage is to ready a bite of food into a bolus for swallowing. This involves grinding and fragmenting the food into smaller pieces appropriate for the pharyngeal stage during mastication as well as the mixing of the food with saliva that begins the digestive process and forms a cohesive bolus. During the oral preparatory stage, the velum is depressed, and breathing is through the nose. A number of oral structures and functions come into play for the oral preparatory stage to successfully occur.

Structures and Physiology of the Oral Preparatory Stage n Lips n

The lips must seal the oral cavity anteriorly to keep food and liquid in the mouth and to prevent it from leaking out of the mouth (Figure 8–1). The orbicularis oris is the primary muscle responsible for maintaining this seal.

n Teeth

The teeth provide the contact surfaces against which food is cut into and bitten and the contact surfaces against which food is masticated. The frontal and lateral incisors act as cutting surfaces for biting into food. The molars act as grinding surfaces for mastication.

n Mandible n

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While the mandible moves only slightly for articulation, it displays a far greater range of motion and force during the act of mastication. The superior/inferior movement of the mandible is used to bring the occlusal surfaces of the lower dental arch to the upper dental arch for the biting of food, such as biting a piece of an apple. The muscles employed for the act of biting are the muscles of mandibular elevation (masseter, anterior fibers of the temporalis, medial pterygoid) and mandibular depression (anterior belly of the digastricus, mylohyoid, geniohyoid, and platysma). 289

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The mandible moves in a rotary motion for the grinding process of mastication. This involves the individual movements of elevation, depression, retraction, protrusion, and lateralization of the mandible all integrated in a coordinated and fairly continuous motion. The side-to-side movement of the mandible during rotary mastication is accomplished via the alternating protrusion and retraction of the left and right temporomandibular joints.

n Tongue n

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n n

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The tongue also acts to crush certain consistencies of food against the hard palate to form a bolus. The back of the tongue is raised during the oral preparatory stage to prevent premature spillage of the contents of the oral cavity into the pharynx and possibly the open airway. Intrinsic and extrinsic tongue muscles are activated to complete these movements. Somatosensory feedback from the tongue, oral cavity, and muscles of mastication is important during mastication. We use sensory input to position food between the teeth, to feel the progression of the breakdown of food, and to track the formation of the bolus. We also use sensory input to avoid inflicting possible injury to ourselves such as biting or chewing the tongue or lips (Miller & Britton, 2011).

Salivary glands n

During and even prior to mastication, the salivary glands begin secretion of saliva.

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Saliva functions to moisturize the bolus to ready it for deglutition and digestion.

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The active component of saliva is the enzyme amylase.

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As the mandible performs its rotary movement during mastication, the tongue performs a similar coordinated action in which the tongue moves to place food between the teeth. Once the teeth have met and grinded the food, the food drops medially back onto the tongue, which then moves to replace the food between the teeth. This process of masticatory tongue movement continues alongside mastication movement of the mandible until the food is appropriately fragmented and formed into a bolus.

During mastication, amylase will begin the process of breaking down starches and glucose for digestion.

Cheeks and buccal cavities n

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The buccal cavities, or buccal space, are the spaces formed within the oral cavity between the cheeks and the lateral dental arches. Tension in the musculature of the cheeks prevents food from falling laterally into the buccal cavities between the mandible and the cheek. This tension is accomplished via contraction of the buccinator muscles. The cheeks assist in mastication further by pressing the bolus into the molars (Cichero & Murdoch, 2006).

Disorders at the Oral Preparatory Stage Any problems or difficulties at the oral preparatory stage, if severe enough to negatively impact mastication or deglutition, are considered oral dysphagia. An exhaustive list and explanation of dysphagia is beyond the scope of this text. However, some examples of oral dysphagias that can occur during the oral preparatory stage include the following: 290

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Difficulty holding the bolus in the oral cavity: Often a lack of appropriate seal of the lips (labial seal, anterior seal) leads to loss of bolus as it spills out between the open lips.

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Difficulty with mastication: This may be caused by a lack of dentition or a lack of appropriate mandibular strength to accomplish appropriate mastication.

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Difficulty with formation or manipulation of bolus: This may be caused by a lack of salivary output as often occurs due to radiation therapy in the treatment of cancer, which makes the creation of an appropriately moist bolus difficult; difficulty moving the tongue appropriately for the formation of the bolus; or spilling of the solid or liquid bolus during mastication anteriorly from between the lips due to inappropriate seal of the lips or posteriorly into the pharynx and possibly into the airway before the individual preparing the bolus is ready for the bolus to enter the pharynx.

Oral Stage Described Once the process of bolus preparation is completed, the oral preparatory stage ends, and the oral stage begins. The function of the oral stage is for the tongue to transport the bolus posteriorly toward the pharynx, triggering the pharyngeal swallow (Figures 8–2 and 8–3).

Structures and Physiology of the Oral Stage n Lips n

The lips stay closed and maintain their seal, and respiration ceases.

n Tongue

During the oral stage of deglutition, mastication ceases, the lips are sealed, the posterior tongue that was raised to prevent the bolus from moving into the pharynx during the oral

FIGURE 8–2.  A lateral view of the soft palate pulled down and forward. Reproduced with permission from Anatomage.

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FIGURE 8–3.  Lateral view of videofluoroscopy displaying a bolus in the oral phase. Source: From Dysphagia Assessment and Treatment Planning, Fourth Edition (p. 9) by Leonard, R., and Kendall, K. Copyright © 2019 Plural Publishing, Inc. All rights reserved. Used with permission.

preparatory stage drops, while the apex of the tongue rises to press against the hard palate. The body of the tongue acts to squeeze the bolus posteriorly toward the oropharynx. n

Anterior faucial pillars n

Once the bolus approximates the posterior oral cavity specifically at the anterior faucial pillars, sensory receptors from the tongue and faucial pillars transmit sensory information to the swallow center of the brainstem that initiates the pharyngeal swallow.

Disorders at the Oral Stage As the primary purposes of the oral stage are to transport the bolus posteriorly and to trigger the pharyngeal swallow, the oral dysphagias that can manifest at this stage present as impairments of these two actions. Examples of oral dysphagias that can occur during the oral stage include the following: n

Difficulties with the anteroposterior movement of the bolus:  Posterior movement of the bolus can be made difficult or impossible by a weakness of the tongue. In oral cancers, sections of the tongue required for this action can be surgically removed, making the movement of the bolus posteriorly by the tongue difficult or impossible, requiring those patients to tilt their head back and rely more on gravity to pull the bolus toward the oropharynx.

n

Difficulties triggering the pharyngeal swallow:  Decreased sensation from the tongue can impair the initiation of the pharyngeal swallow.

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Pharyngeal Stage Described

FIGURE 8–4.  Lateral view of videofluoroscopy of bolus moving from pharyngeal into esophageal phase. Source: From Dysphagia Assessment and Treatment Planning, Fourth Edition (p. 15) by Leonard, R., and Kendall, K. Copyright © 2019 Plural Publishing, Inc. All rights reserved. Used with permission.

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For the biological process of eating and drinking, the importance of the pharynx cannot be overstated. It is the cavity that connects the oral cavity to the esophagus. All hydration and nutrition that pass into the body through the mouth pass through the pharynx into the esophagus. As the pharyngeal swallow is cued, it activates a number of finely coordinated and very quick individual actions by the structures of the pharynx. Because the pharyngeal swallow is reflexive, these actions are below the level of awareness. In short, you are aware that you are swallowing and that you initiated the act, but you are unaware of all the individual structures and movements of these structures that allow the pharyngeal swallow to be accomplished. The physiology of the structures of the pharynx during the pharyngeal stage of the swallow is outlined in more detail later. But it is important to realize that none of these actions will occur if the pharyngeal swallow is not triggered. The purposes of the pharyngeal stage of the swallow are to move the bolus safely over the airway, not allowing any penetration or aspiration of the bolus into the airway, and to deliver the bolus into the esophagus (Figure 8–4). Take a moment to consider the task of the pharyngeal stage of keeping all materials to be swallowed out of the airway. This is a serious issue because there is a significant design flaw in the human body, an ever-present challenge, in that the bolus must always be passed safely over the airway to be swallowed. This is because the airway is anterior to the esophagus. If the pharynx does not accomplish this successfully often enough, then sickness from aspiration pneumonia, malnutrition, dehydration, and death become more likely. So, the body has developed the pharyngeal swallow, a fine-tuned and complex

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

reflexive action, to meet this challenge. If a person loses the ability to carry out the pharyngeal swallow, then taking food and water safely by mouth becomes very difficult or impossible.

Structures and Physiology of the Pharyngeal Stage n Velum n

n

n

n

n

n

n

As the pharyngeal stage of the swallow is initiated, the epiglottis is inverted and depressed to meet and seal off the entry way to the larynx, the aditus of the larynx, as it is elevated. The aryepiglottic muscles contract to depress the epiglottis and the suprahyoid muscles (digastric, geniohyoid, mylohyoid, and stylohyoid) contract to elevate the larynx. These two actions work to squeeze the epiglottis against the superior larynx, forming the first and superior-most level of airway protection. Simultaneously, the true vocal folds and false vocal folds are adducted tightly over the airway, forming the second and third levels of airway protection. The muscles of vocal fold adduction are important to this action. The transverse and oblique interarytenoids are important for this medial compression of the true vocal folds during a swallow. During the pharyngeal stage of the swallow, the base of the tongue retracts posteriorly to contact the posterior pharyngeal wall that is simultaneously being pulled anteriorly to propel the bolus toward the esophagus. Inferior fibers of the superior pharyngeal constrictor connect to the base of the tongue and are responsible for both the posterior retraction of the tongue and the anterior movement of the posterior pharyngeal wall.

Muscles of pharyngeal elevation n

n

n

The airway has three levels of structures that seal off and protect the airway from aspiration and penetration during the pharyngeal stage of the swallow. These are the epiglottis, the true vocal folds, and the false vocal folds.

Base of the tongue n

n

Elevators of the velum are levator veli palatini, musculus uvulae, and tensor veli palatini.

Epiglottis, true vocal folds, false vocal folds n

n

During the pharyngeal stage, the velum elevates, closing and sealing the velopharyngeal port, to prevent material being swallowed from entering the nasal cavity.

By elevating the pharynx, the distance between the upper esophageal sphincter and the oral cavity is decreased, thereby decreasing the distance the bolus must travel through the pharynx before reaching the esophagus. The muscles of pharyngeal elevation include palatopharyngeus, salpingopharyngeus, and stylopharyngeus.

Pharyngeal constrictors n

n

During the pharyngeal stage of the swallow, the walls of the pharynx constrict to guide and propel the bolus over the airway and inferiorly to the esophagus. This coordinated constriction is pharyngeal peristalsis. The primary muscles of the pharynx accomplishing this constriction are the superior and middle pharyngeal constrictors. The superior portion of the inferior pharyngeal constrictor, the thyropharyngeal muscle, also constricts to propel the bolus toward the esophagus. 294

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The inferior portion of the inferior pharyngeal constrictor is the cricopharyngeal muscle. The cricopharyngeal muscle is the muscular component of the upper esophageal sphincter, the ringlike muscle that, contracted, keeps the esophagus sealed. As the superior and middle pharyngeal constrictors and thyropharyngeal muscle are contracting to pass the bolus through the pharynx, toward the esophagus, the cricopharyngeal muscle relaxes, opening the esophagus to allow the bolus to pass into the esophagus.

Disorders at the Pharyngeal Stage Given the complexity of the pharyngeal stage of the swallow, disorders of the pharyngeal stage of deglutition are numerous and varied. Some examples of pharyngeal dysphagia include the following: A delayed or absent pharyngeal swallow:  If the bolus enters the pharynx and stays there with no initiation of the pharyngeal swallow for 10 s or more, there is said to be an absent pharyngeal swallow. If the pharyngeal swallow is cued after the bolus passes into the pharynx but prior to 10 s, there is said to be a delayed pharyngeal swallow. If the pharyngeal swallow is absent or is too delayed, then none of the reflexively automatic actions of the pharyngeal stage of the swallow are initiated or they are initiated after the bolus has already fallen into the pharynx. An absent or delayed pharyngeal swallow is highly problematic because there is bolus material entering the pharynx without all the reflexive actions taken to seal off the airway to protect the lungs from penetration and aspiration. See Figure 8–5 for an image of a liquid bolus sitting in the vallecula of the pharynx waiting on the pharyngeal swallow to occur. Note in Figure 8–5 the

FIGURE 8–5.  Lateral view of videofluoroscopy showing bolus pouring into pharynx and about to penetrate into airway. Source: From Dysphagia Assessment and Treatment Planning, Fourth Edition (p. 58) by Leonard, R., and Kendall, K. Copyright © 2019 Plural Publishing, Inc. All rights reserved. Used with permission.

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epiglottis at rest and the airway fully open to the pharynx as the bolus courses over the epiglottis and approaches the airway. n

A lack of pharyngeal constriction: If the pharynx is not constricting and elevating enough, or the base of the tongue lacks appropriate retraction, the bolus will not be routed and held together appropriately during the pharyngeal stage, and bolus residue is likely to remain in the pharynx after deglutition. This bolus residue, called pharyngeal stasis, can penetrate or aspirate into the airway well after deglutition is complete and the airway is fully open and exposed for respiration (Figure 8–6).

n

A lack of laryngeal elevation: Laryngeal elevation is an important component to sealing off the airway with the epiglottis during the pharyngeal stage. Without appropriate laryngeal elevation during a swallow, the aditus of the larynx is not closed off, which can allow a bolus to penetrate or aspirate into the airway. A lack of laryngeal elevation can be felt by the clinician as reduced anterior and superior movement of the patient’s thyroid cartilage during a swallow.

n

A lack of adduction of the vocal folds during the pharyngeal swallow: In addition to laryngeal elevation and epiglottic inversion, the adduction of the vocal folds is important for the protection of the airway from penetration (Figure 8–7) and aspiration (Figure 8–8). Note in Figure 8–8 that part of the liquid bolus has entered the airway and is coursing down the anterior wall of the trachea creating a dark thin line quite anterior from the pharynx which is full of the liquid barium bolus.

n

A lack of dilation of the upper esophageal sphincter: If the upper esophageal sphincter cannot dilate or relax enough to receive a bolus, then the food becomes stuck in the patient’s pharynx. These patients often report difficulty “getting food down” and will usually independently learn

FIGURE 8–6.  Fiberoptic endoscopic evaluation of swallowing view showing large amount of bolus residue (stasis) in the hypopharynx after a swallow with no viewable penetration. Source: From Clinical Management of Swallowing Disorders, Fifth Edition (p. 43) by Murry, T., Carrau, R. L., and Chan, K. Copyright © 2022 Plural Publishing, Inc. All rights reserved. Used with permission.

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FIGURE 8–7.  An example of a fiberoptic endo­ scopic evaluation of swallowing view of penetration to the level of the vocal folds. Source: From Clinical Management of Swallowing Disorders, Fifth Edition (p. 7) by Murry, T., Carrau, R. L., and Chan, K. Copyright © 2022 Plural Publishing, Inc. All rights reserved. Used with permission.

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FIGURE 8–8. Significant aspiration as barium flows down the anterior tracheal wall as the majority of the bolus passes posteriorly through the pharynx into the esophagus. Source: From Clinical Management of Swallowing Disorders, Fifth Edition (p. 136) by Murry, T., Carrau, R. L., and Chan, K. Copyright © 2022 Plural Publishing, Inc. All rights reserved. Used with permission.

to avoid the types of food that create these difficulties for them and will learn to take much smaller bites to accommodate this difficulty.

Once the bolus enters the esophagus from the pharynx through the upper esophageal sphincter, the esophageal stage of the swallow has begun (Figure 8–9). The esophageal stage is the fourth and final stage of deglutition (Figure 8–10). The esophagus is a collapsed tube of muscle that connects the pharynx to the stomach and is under the control of the autonomic nervous system. The esophagus is divided into three sections. The cervical esophagus is the most superior section and is composed of striated muscle. The middle third is the thoracic esophagus, and this is where the striated muscle transitions into true smooth muscle of the digestive tract. The abdominal esophagus is the inferior third of the esophagus and is composed of smooth muscle. The esophagus is bounded superiorly and inferiorly by two sphincters (Figure 8–11). The superior one that opens the upper esophagus into the pharynx is the upper esophageal sphincter. The inferior 297

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Esophageal Stage Described

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 8–9. The bolus in the cervical esophagus and cricopharyngeal region. Reproduced with permission from Anatomage.

FIGURE 8–10. Bolus of barium passing through esophageal stage during videofluoroscopy. Source: From Dysphagia Assessment and Treatment Planning, Fourth Edition (p. 81) by Leonard, R., and Kendall, K. Copyright © 2019 Plural Publishing, Inc. All rights reserved. Used with permission.

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FIGURE 8–11.  Esophagus, stomach, and upper and lower esophageal sphincters. Reproduced with permission from Anatomage.

one that controls admittance of the bolus from the esophagus into the stomach is the lower esophageal sphincter. These two sphincters remain contracted and tight unless allowing a bolus to pass, thereby preventing reflux and regurgitation of stomach contents. Once a bolus enters into the esophagus, a coordinated autonomic series of constrictions of the walls of the esophagus known as esophageal peristalsis propels the bolus inferiorly to be deposited in the stomach.

Structures and Physiology of the Esophageal Stage

Disorders at the Esophageal Stage As the esophagus is under autonomic control, there is little the speech-language pathologist can do or ask the patient to do that can affect this stage of deglutition. Therefore, treatment for esophageal disorders is in the realm of medical or surgical treatment and not within the field of speech-language pathology. However, the speech-language pathologist must be able to recognize esophageal-stage disorders and differentiate them and their symptoms from pharyngeal-stage disorders for the purposes of appropriate referral. Examples of esophageal-stage disorders include the following: 299

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Compared to the elaborate coordination of many structures and functions of the pharyngeal swallow, the esophageal stage is relatively simple. The esophageal stage is characterized by a descending wave of peristaltic contraction of the esophagus carrying the bolus from the pharynx to the stomach. When the bolus is transported into the cervical esophagus from the upper esophageal sphincter, the upper esophageal sphincter tightens behind the bolus to prevent reflux or regurgitation. The esophagus quickly squeezes the bolus inferiorly via peristalsis to the lower esophageal sphincter. The lower esophageal sphincter relaxes and allows the bolus to pass into the stomach, where the process of digestion and absorption continues. The transit time of a bolus through the esophageal stage varies according to bolus consistency and size. The time range of a normal bolus transit is normally between 8 and 20 s (Dodds et al., 1973; Mandelstam & Lieber, 1970).

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

n

Esophageal motility disorder:  Occurs when the duration and/or amplitude of esophageal peristalsis is uncoordinated, too weak, or too strong. This can inhibit the successful and normal transport of the bolus through the esophagus, slowing or stopping the transport or reversing the bolus superiorly to be refluxed into the pharynx. One example of an esophageal motility disorder is fibromuscular esophageal stenosis in which a length of the smooth muscle of the esophagus has inappropriately constricted to create an obstacle for the descending bolus (Figure 8–12).

FIGURE 8–12.  Coronal view of videofluoroscopy of esophageal stage being interrupted by fibromuscular esophageal stenosis (indicated by yellow arrow). Source: From Dysphagia Assessment and Treatment Planning, Fourth Edition (p. 81) by Leonard, R., and Kendall, K. Copyright © 2019 Plural Publishing, Inc. All rights reserved. Used with permission.

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n

Zenker diverticulum:  This is an abnormal and acquired pouchlike structure in the hypopharynx that is related to decreased dilation of the upper esophageal sphincter due to sustained contraction of the cricopharyngeal muscle during deglutition (Figure 8–13). When the upper esophageal sphincter fails to relax and open appropriately, this puts increased pressure on the posterior wall of the hypopharynx. Over time, this pressure forces the mucosal and submucosal tissues of the hypopharynx to be pushed out into a pouchlike structure at a point of muscular weakness of the posterior inferior pharyngeal wall. Common symptoms include dysphagia, regurgitation (Bizotto et al., 2013), and bad breath.

n

Esophageal rings/webs:  These lesions are bands of mucosal/submucosal tissue that form points of constriction within the esophagus. The term ring is used when the constriction is located at the esophagogastric junction, where the esophagus connects to the stomach. The most common esophageal ring is Schatzki ring (Figure 8–14). These are idiopathic though commonly associated with a hiatal hernia and can cause dysphagia and occlusion of the esophagus. The term web is used when the bandlike constriction occurs more superiorly in the esophagus or hypopharynx.

FIGURE 8–13.  Zenker diverticulum seen in the image posterior to the normal pharyngoesophageal path of the bolus. Source: From Clinical Management of Swallowing Disorders, Fifth Edition (p. 79) by Murry, T., Carrau, R. L., and Chan, K. Copyright © 2022 Plural Publishing, Inc. All rights reserved. Used with permission.

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FIGURE 8–14.  Schatzki ring. Source: From Clinical Management of Swallowing Disorders, Fifth Edition (p. 76) by Murry, T., Carrau, R. L., and Chan, K. Copyright © 2022 Plural Publishing, Inc. All rights reserved. Used with permission. Adapted from Comprehensive Management of Swallowing Disorders, Second Edition (p. 192) by Carrau, R., and Murry, T. Copyright © 2017 Plural Publishing, Inc. All rights reserved. Used with permission.

n

Esophagitis:  This is an inflammation of the linings of the esophagus (Figure 8–15). Usually, this inflammation is associated with stomach acid passing through the lower esophageal sphincter to irritate and damage mucosal linings of the esophagus. It is also commonly caused when someone is taking a pill by mouth and the pill lodges in the esophagus prior to the stomach where it slowly dissolves, damaging and irritating the esophageal lining.

➤ Instrumentation Videofluoroscopic Swallow Study/Modified Barium Swallow Often referred to as the golden standard of swallow evaluations, videofluoroscopy has been in use for decades. This procedure is known as a videofluoroscopic swallow study (VFSS) or a modified barium swallow study (MBSS). During this procedure, patients consume varying consistencies of liquids and 302

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solids mixed with barium, a radiopaque substance, in a radiology suite with x-rays passing through their head and neck as they consume the barium. This shows the passage of the barium through the oral and pharyngeal stages of the swallow (Figures 8–3, 8–4, 8–5, 8–8, 8–10, and 8–13). During VFSS/ MBSS, clinicians are able to readily view, via the movement of the barium, the relevant anatomy of all structures involved in mastication and deglutition as well as the progression of the bolus through the oral and pharyngeal cavities. During VFSS/MBSS, the speech-language pathologist can view and detect the presence of dysphagia during such instances of penetration/aspiration when the barium passes into the airway (Figure 8–8), and pharyngeal stasis when some or all of the barium-laced bolus stays in the pharynx after the pharyngeal swallow. Clinicians also trial therapy strategies such as altered posture, and altered consistencies of solid foods and liquids, during VFSS/MBSS to determine the degree to which swallow function can be improved in the immediate short term. The primary drawback to VFSS/MBSS is that fluoroscopy requires exposing patients to ionizing radiation (x-ray), and so the more time spent visualizing the swallow during an VFSS/MBSS, the more radiation a patient is exposed to. In addition, a patient must be transported to a facility that has the necessary staff and radiology equipment if this does not exist where the patient currently is.

Fiberoptic Endoscopic Evaluation of Swallow During a fiberoptic endoscopic evaluation of swallow (FEES), a fiberoptic endoscope (Figure 8–16) is threaded through the nasal cavity of the patient posteriorly into the nasopharynx. From there, the 303

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FIGURE 8–15.  Esophagitis (lower two quadrants). Source: From Clinical Management of Swallowing Disorders, Fifth Edition (p. 61) by Murry, T., Carrau, R. L., and Chan, K. Copyright © 2022 Plural Publishing, Inc. All rights reserved. Used with permission.

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 8–16.  Speech-language pathologist conducting a fiberoptic endoscopic examination. Source: From Clinical Management of Swallowing Disorders, Fifth Edition (p. 133) by Murry, T., Carrau, R. L., and Chan, K. Copyright © 2022 Plural Publishing, Inc. All rights reserved. Used with permission.

fiberoptic endoscope can peer inferiorly into the pharynx and larynx to observe anatomy, physiology, and features of deglutition during the swallow (Figures 8–6 and 8–7). Unlike the VFSS/MBSS, a FEES does not expose the patient to radiation and is highly mobile, these days requiring only a laptop computer and the endoscope, so the speech-language pathologist can come directly to the patient’s hospital room or home if necessary to carry out the swallow evaluation. Because a FEES does not expose a patient to radiation, the clinician can spend far more time assessing the swallow for dysphagia and trialing different therapy strategies to remediate possible dysphagia than is advisable during a VFSS/MBSS. Some drawbacks to FEES is that the oral preparatory and oral phases are not observable through the fiberoptic endoscope. In addition, when the pharyngeal swallow is executed, the pharynx constricts, as a part of the pharyngeal swallow, around the fiberoptic endoscope creating a brief moment where the fiberoptic endoscope is blinded by the pharyngeal tissue constricting around it. This brief period renders the speech-language pathologist unable to visualize what actually occurred during the pharyngeal swallow and is known as the whiteout. However, the clinician does see everything happening in the pharynx up to the initiation of the pharyngeal swallow and the occurrence of the whiteout and everything directly after the pharyngeal swallow and the whiteout and is able to make educated conclusions about swallow functionality and the presence or absence of dysphagia.

High-Resolution Manometry Although VFSS and FEES have allowed for the visual evaluation of different aspects of pharyngeal swallow, these methods leave the speech-language pathologist largely blind to any changes in the necessary pharyngeal pressures during the pharyngeal swallow that propel the bolus safely through the pharynx into the esophagus. High-resolution manometry (HRM) has recently been applied to address this gap 304

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in the evaluation of pharyngeal dysphagia. HRM is capable of evaluating the changes in pharyngeal pressures during deglutition and allowing for the detection of insufficient or abnormal levels of pharyngeal pressure. In this method of swallow evaluation, a manometric catheter is passed through the pharynx to measure changes in pharyngeal pressures during the swallow. See Figure 8–17 where a manometric catheter has been placed in the pharynx during an MBSS. Few speech-language pathologists use or have access to the use of HRM for evaluation of swallow. Ryu et al. (2015) hypothesize that HRM for the evaluation of swallow has not made it into standard clinical practice yet due to limitations such as the lack of ability to detect aspiration/penetration and pharyngeal stasis, which are two frequent and obvious concerns of a speech-language pathologist during most swallow evaluations. However, some clinicians such as Knigge et al. (2014) advocate for using HRM alongside other methods such as VFSS and FEES to enhance the assessment of complex cases of dysphagia.

➤ Changes With Age Childhood Development As the human body develops from infancy through childhood to adulthood, many changes in the anatomy and physiology involved in mastication and deglutition occur.

Anatomical Differences in Infant and Later Childhood and Adulthood

FIGURE 8–17. A radiograph showing manometry sensor to study esophageal-stage swallow. Source: From Clinical Management of Swallowing Disorders, Fifth Edition (p. 133) by Murry, T., Carrau, R. L., and Chan, K. Copyright © 2022 Plural Publishing, Inc. All rights reserved. Used with permission.

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At birth and infancy, the oral-pharyngeal anatomy is far different from that of an adult. This makes sense as one considers that an infant begins its life taking only fluids by mouth and does not yet take solids;

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

therefore, the teeth and the volitional fine motor ability of the mandible and tongue are not required for mastication and deglutition of solids. Anatomical differences affecting swallowing between infancy and adulthood include the following: n

The oral cavity of an infant is much smaller and the tongue takes up much more of the oral cavity than in an adult. This is conducive to the primary function of the tongue during feeding at this age, which is not the large range-of-motion, side-to-side movement of an adult tongue forming a solid bolus between the dental arches but the slight up-and-down, anterior and posterior movement of the baby’s tongue compressing against the hard palate as the infant suctions milk from the breast or bottle. n Infants often also have larger buccal fat pads in their cheeks that facilitates the labial seal, the infant’s latch, onto the nipple of the breast or bottle. n The mandible is much smaller and less developed in infants than in adults. As the infant grows, the mandible becomes larger and lowers, thereby increasing the size of the oral cavity (Figure 8–18). n In infants, the hyoid and larynx are far more superior in the neck than the hyoid and larynx of an adult (Figure 8–18). As a result of this, the epiglottis tends to reach more superiorly and the velum inferiorly. This closeness of these structures provides more protection for the airway during the swallow. In some infants, the epiglottis is so high in the pharynx that

Adult Child

Tongue Pharynx

Tongue

Pharynx

Epiglottis

Epiglottis

Vocal folds

Vocal folds Cricoid

Cricoid

Trachea

Trachea

Lungs

Lungs

FIGURE 8–18.  Lateral view comparing infant and adult head and neck structures. Source: From Clinical Management of Swallowing Disorders, Fifth Edition (p. 218) by Murry, T., Carrau, R. L., and Chan, K. Copyright © 2022 Plural Publishing, Inc. All rights reserved. Used with permission.

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the tip of the epiglottis can be visualized looking through the oral cavity at the back of the throat with a flashlight.

Physiology of Deglutition at Infancy In adults and older children, feeding is a voluntary activity; in infants, it begins entirely reflexive in nature. There are an assorted number of infantile reflexes originating at the brainstem which mediate an infants’ feeding. As infants mature, their pattern of swallow changes and becomes more adultlike and volitional as they progress from infancy through childhood to adulthood: n

Infants begin life subsisting entirely on fluids with an instinctive aversion to solids. By 6 months, most infants begin to eat some puree-consistency solids while still gaining most nutrients from fluids. Around 10 months of age, the child’s motor development has increased to allow them to begin taking some ground/mashed solids in addition to purees and liquids. At about 12 to 15 months of age, some small, solid pieces of table food are being consumed. By 24 months of age, most solids are able to be masticated and swallowed.

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At birth to about 6 months of age, infants display an oral stage pattern of suckle feeding that is reflexive and characterized by a loose labial seal (a loose seal of the baby’s lips on the nipple), with the tongue sealing around the nipple, and using a rhythmic simple front-to-back movement of the tongue against the nipple to pull milk from the breast or bottle.

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At 2 months of age, most infants will pull from the nipple more than once and collect a larger liquid bolus before swallowing, though 25% of infants will swallow after each suck of the nipple (Newman et al., 1991).

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Around 6 months of age, suckle feeding progresses to a more advance sucking feeding pattern. Sucking is characterized by a tight labial seal (a tight seal of the baby’s lips on the nipple), with less seal of the tongue and a rhythmic, more vertical movement of the tongue as it compresses the nipple against the hard palate.

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As an infant’s motor skills develop, their feeding evolves from the reflexive suckle to the sucking feeding pattern. Soon they gain volitional control during sucking, and eventually the child’s feeding abilities expand to include the more sophisticated motor skills necessary for a diet of all consistencies of solids and liquids.

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This increase in volitional control of the oral stage continues as the child’s motor skills become more developed and refined: They learn to take food off a spoon and fork, their postural support increases to allow the child to sit upright during feeding, their ability to bite and chew emerges, hand-to-mouth and self-feeding skills are refined, the mandible develops a greater range of motion and develops the rotary movements of mastication for future mastication, and movement of the tongue becomes more advanced as well.

Changes With Normal Aging Presbyphagia As the human body ages, it undergoes expected anatomical changes and physiological declines in function that negatively affect mastication and deglutition. Some of these changes are ossification of the hyoid, thyroid, cricoid cartilages, atrophy of lingual, laryngeal, and pharyngeal musculature (Cichero, 2018; Mancopes et al., 2021). These anatomical changes create associated reductions in hyolaryngeal 307

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excursion, pharyngeal constriction, and lingual pressure during swallow used to propel the bolus through the pharynx quickly (Cichero, 2018; Mancopes et al., 2021). Also, a loss in dentition and muscle mass of the muscles of mastication results in reduced bite force and an overall decreased chewing efficiency (Cichero, 2018; Kim et al., 2021; Mancopes et al., 2021). The degree to which these normal anatomical and physiological changes with age reduce the efficiency of mastication and deglutition is known as presbyphagia. It is important to note that presbyphagia characterizes a normal healthy swallow of an older individual, albeit a less efficient swallow than that same individual would have displayed as a younger adult. Presbyphagia does not automatically imply the presence of swallow disorder or a lack of disfunction, which would be dysphagia. However, a slower and less efficient swallow makes elderly individuals more vulnerable to disruptions to their mastication and deglutition processes which can create dysphagia more readily than in a younger population of adults.

Sense of Taste The sensory system generating taste is known as the gustatory system and arises from taste receptor cells located on the tongue and the palatal epithelium within specialized organs known as taste buds (Iwata et al., 2014). These receptor cells detect chemical compounds in food for food recognition, monitoring of food intake, saliva production, and generation of the five basic tastes: sweet, salty, bitter, sour, and umami (Iwata et al., 2014). These tastes inform us of the nature of what is in our mouths and allows us to determine if it is food and, if so, what kind of food. The taste of sweetness allows us to recognize carbohydrates, salty allows us to recognize and regulate sodium intake, sour allows us to determine the ripeness of fruits and avoid toxic substances such as spoiled food, bitterness functions to help us avoid eating something toxic or harmful, and finally, our sense of umami is a meat taste and ensures we are able to sense protein (Iwata et al., 2014).

Umami is the most recently added word to the list of our taste senses. This is the Japanese word given to the savory taste of cooked meats, broths, and some fermented food. Foods that provide amino acids and proteins have strong umami taste, such as meats, broths, fish, shellfish, some vegetables such as tomatoes and mushrooms, and strong aged cheeses. As amino acids and proteins are essential to the function and development of the brain and body, our sense of umami allows humans to hunt for and detect these nutrients in foods.

Sense of taste and smell reduces with age (Cowart, 1989). Results by Solemdal et al. (2012) indicate that among the hospitalized elderly population, taste sensation was reduced or altered. Older adults with a reduced and altered sense of taste and smell may find food less appetizing, have a decreased sense of hunger, and consume less. These changes may potentially contribute to malnutrition in the elderly (Kaneda et al., 2000). However, maintaining good oral health and reducing decayed teeth, oral bacteria growth, and dry mouth may help better preserve the sense of taste in the elderly population (Solemdal et al., 2012). In some cases of neurogenic dysphagia, speech-language pathologists can use strong bitter or sour flavors, such as lemon, to stimulate the client’s gustatory system to elicit a stronger, more functional pharyngeal swallow and more hyolaryngeal elevation in their patients (Dafiah & Swapna, 2020; Pauloski & Nasir, 2016). 308

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➤ Coordination of Respiration and Deglutition An important aspect of a safe and successful pharyngeal swallow is the appropriate coordination and timing of respiration and the pharyngeal swallow. As a person is eating, respiration occurs during the oral preparatory, oral, and esophageal stages of the swallow. However, respiration must cease during the pharyngeal swallow as the airway is sealed for protection as the bolus passes over the airway through the pharynx on its way to the esophagus. As signals for the autonomic process of respiration and the reflexive actions of the pharyngeal swallow both originate at the brainstem, there is a high degree of automaticity involved in coordinating these actions. Most adults will automatically time the onset of the pharyngeal swallow to occur during the respiratory cycle after an inspiration. This causes respiration to be ceased for a short period before or during expiration (Martin et al., 1994; Preiksaitis et al., 1992; Selley et al., 1989). This timing of the passage of the bolus over the airway before or during expiration ensures that if any aspiration or penetration occurs, the body will have air in the lungs to immediately be able to cough and clear the airway. To avoid aspiration, infants’ bodies must also successfully coordinate their respiration and swallow from the moment they begin to take milk. As infants at birth have no intentional reasoning capability, this successful coordination rests solidly on their autonomic respiration and a number of primitive reflexes that normally allow an infant to automatically and safely take nutrition by mouth from the breast or nipple. The disruption of the coordination of respiration and the pharyngeal swallow in adults, children, or infants by neurological disease or neurological damage such as that caused by stroke or traumatic brain injury is a possible cause of pharyngeal dysphagia. The loss of or decreased ability to successfully coordinate respiration with their pharyngeal swallow often predisposes these individuals to aspiration and penetration. As such, it is often the role of the speech-language pathologist to carefully observe the patients’ respiration during meals to monitor for problems between these two functions. This is especially true in the treatment of infants born prematurely, whose bodies are incapable of successfully accomplishing the fine balancing of respiration and deglutition to successfully accomplish both. As such, these infants are at increased risk of aspiration and penetration and may also show lower than appropriate levels of oxygen in their bloodstream as their bodies are breathing too little during feedings.

Understanding the unimpaired process of mastication and swallowing is paramount to understand prior to learning and understanding disordered swallowing. The swallowing process involves the oral cavity, pharynx, larynx, and esophagus. The purpose of mastication is to prepare food into a swallow-ready mass known as a bolus. The purpose of deglutition, or swallowing, is to transition the bolus from the oral cavity to the stomach. If any foreign material such as saliva or bolus material enters the airway, it is categorized in one of two ways: aspiration, when foreign material passes into the airway below the true vocal folds, or penetration, when foreign material passes into the airway but does not pass below the true vocal folds. The process of mastication and deglutition occurs in four stages: oral preparatory stage, oral stage, pharyngeal stage, and esophageal stage. During the oral preparatory stage, a bite of food is prepared into a cohesive bolus by grinding and fragmenting the food into smaller pieces and mixing the food with saliva to ready the bolus for

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➤ Chapter Summary

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

the swallow. Various oral structures are important in this stage, including the lips, teeth, mandible, tongue, salivary glands, cheeks, and buccal cavity. Any problems or difficulties at this stage are considered an oral dysphagia, such as difficulties with mastication or difficulties with formation or manipulation of the bolus. The oral stage begins once the process of bolus preparation is complete; the main function of this stage is for the tongue to transport the bolus posteriorly toward the pharynx, triggering the pharyngeal stage of the swallow. Structures involved in this stage include the lips, tongue, and anterior faucial pillars. Difficulties with this stage are also considered oral dysphagias. Oral dysphagias that can occur during this stage include difficulties with the anteroposterior movement of the bolus and difficulties triggering the pharyngeal swallow. The pharyngeal stage begins once the bolus enters the pharynx and reaches the vallecula. In this stage, the purpose is to move the bolus safely over the airway, not allowing any penetration or aspiration of the bolus into the airway, and to deliver the bolus into the esophagus. If consistent safe transfer of the bolus over the airway is not successful, it can cause sickness from aspiration pneumonia, malnutrition, dehydration, and death. Structures involved in this stage include the velum, epiglottis, true vocal folds, false vocal folds, base of the tongue, muscles of pharyngeal elevation, and pharyngeal constrictors. Any problems or difficulties at this stage are considered a pharyngeal dysphagia; these include a delayed or absent pharyngeal swallow, a lack of pharyngeal constriction, a lack of laryngeal elevation, a lack of adduction of the vocal folds during the pharyngeal swallow, or a lack of dilation of the upper esophageal sphincter. The pharyngeal stage ends and the esophageal stage begins once the bolus enters the esophagus from the pharynx through the upper esophageal sphincter. The esophagus is divided into three sections: the cervical esophagus, the thoracic esophagus, and the abdominal esophagus. The esophagus is bounded superiorly by the upper esophageal sphincter, which opens the upper esophagus into the pharynx, and inferiorly by the lower esophageal sphincter, which controls admittance of the bolus from the esophagus into the stomach. The bolus is propelled inferiorly and deposited into the stomach through a coordinated autonomic series of constrictions of the walls of the esophagus known as esophageal peristalsis. Treatment for esophageal disorders is not within the field of speech-language pathology. However, speech-language pathologists need to be able to recognize esophageal disorders and differentiate them and their symptoms from pharyngeal disorders in order to make appropriate patient referrals. Examples of esophageal disorders include esophageal motility disorder, Zenker diverticulum, esophageal rings or webs, and esophagitis. During a videofluoroscopic swallow study (VFSS), also known as a modified barium swallow study (MBSS), patients consume varying consistencies of liquids and solids mixed with barium, a radiopaque substance, in a radiology suite with x-rays passing through their head and neck as they consume the barium, showing the passage of the barium through the oral and pharyngeal stages of the swallow. VFSS allows clinicians to view the oral preparatory, oral, pharyngeal, and perhaps esophageal stages of a swallow. During a fiberoptic endoscopic evaluation of swallow (FEES), a fiberoptic endoscope is threaded through the nasal cavity of the patient posteriorly into the nasopharynx. FEES allows the clinician to observe what is happening in the pharynx up to the constriction of the pharynx that leads to the camera being blinded in a moment known as the whiteout, then everything directly after the whiteout can also be observed. This allows the clinician to directly observe pharyngeal dysphagias or to make educated conclusions about swallow functionality and the presence or absence of dysphagia. High-resolution manometry (HRM)

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is capable of evaluating the changes in pharyngeal pressures during deglutition and allowing for the detection of insufficient or abnormal levels of pharyngeal pressure. In this method of swallow evaluation, a manometric catheter is passed through the pharynx to measure changes in pharyngeal pressures during the swallow. Few speech-language pathologists use or have access to the use of HRM for evaluation of swallow. As the human body develops from infancy through childhood to adulthood, many changes in the anatomy and physiology involved in mastication and deglutition occur. The oral cavity of infants is smaller and the tongue uses up more space than in the oral cavity of an adult. Infants also have large fat pads in their cheeks to facilitate feeding. Their hyoid and larynx are far more superior in their neck than in an adult, and their epiglottis reaches far more superiorly in the pharynx while their velum reaches more inferiorly. Patterns of feeding change as infants grow into childhood then adulthood. Infants begin life by taking fluids by mouth and evolve to taking purees around 6 months, ground-up/mashed solids around 10 months, and small pieces of table food around 12 to 15 months; by 24 months, the child is able to masticate and swallow all normal consistencies. From birth to 6 months, infants display the suckle feeding pattern that evolves to a more sophisticated and volitional sucking feeding pattern after 6 months. As their motor abilities increase, their ability to masticate improves, and their ability to successfully take different consistencies of solids becomes more advanced. Once the body passes the prime of youth, it undergoes expected anatomical changes and physiological declines in function that negatively affect mastication and deglutition — these are known as presbyphagia. Some of these changes are ossification of the hyoid, thyroid, and cricoid cartilages; atrophy of lingual, laryngeal, and pharyngeal musculature; loss of dentition; and loss of muscle mass of the muscles of mastication, resulting in decreased efficiency of mastication. Presbyphagia is not disordered mastication and deglutition, but it is a less efficient version of mastication and deglutition within the range of normal. The sensory system generating taste is known as the gustatory system and arises from taste receptor cells located on the tongue and the palatal epithelium within specialized organs known as taste buds. These receptor cells detect chemical compounds in food for food recognition, monitoring of food intake, saliva production, and generation of the five basic tastes: sweet, salty, bitter, sour, and umami. A person’s sense of taste becomes less sensitive with age, causing older adults to find food less appetizing, have a decreased sense of hunger, and consume less. Coordination of respiration and deglutition is essential to successful completion of these two life-giving functions. Respiration occurs during the oral preparatory, oral, and esophageal stages of the swallow but must cease during the pharyngeal swallow because the airway is sealed for protection as the bolus passes over the airway through the pharynx on its way to the esophagus. Most adults will automatically time the onset of the pharyngeal swallow to occur during the respiratory cycle after an inspiration. This ensures that the body will have air in the lungs to immediately be able to cough and clear the airway if there is any aspiration or penetration. The disruption of the smoothly coordinated actions of respiration and deglutition is a cause of pharyngeal dysphagia and is not uncommon in the caseload of the speech-language pathologist working with adults or small children.

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➤ References Bizotto, A., Iacopini, F., Landi, R., & Costamagna, G. (2013). Zenker’s diverticulum: Exploring treatment options. ACTA Otorhinolaryngologica Italica, 33(4), 219–229. Cichero, J. (2018). Age-related changes to eating and swallowing impact frailty: Aspiration, choking risk, modified food texture, and autonomy of choice. Geriatrics, 3(4), 69. Cichero, J., & Murdoch, B. (2006). Dysphagia: Foundation, theory, and practice. John Wiley & Sons. Cowart, B. J. (1989). Relationships between taste and smell across the adult life span. Annals of the New York Academy of Sciences, 561(1), 39–55. https:// doi.org/10.1111/j.1749-6632.1989.tb20968.x Dafiah, P. M., & Swapna, N. (2020). Variations in amplitude and duration of hyolaryngeal elevation during swallow: Effect of sour and carbonated liquid bolus. Physiology and Behavior, 224, 113028. https://doi.org/10.1016/j.physbeh.2020.113028 Dodds, W. J., Hogan, W., Reid, D., Stewart, E., & Arndorfer, R. (1973). A comparison between primary esophageal peristalsis following wet and dry swallows. Journal of Applied Physiology, 35, 851–857. Iwata, S., Yoshida, R., & Ninomiya, Y. (2014). Taste transductions in taste receptor cells: Basic tastes and moreover. Current Pharmaceutical Design, 20(16), 2684–2692. Jean, A. (2001). Brain stem control of swallowing neuronal network and cellular mechanisms. Physiological Reviews, 81(2), 929–969. https://doi.org/​ 10.1152/physrev.2001.81.2.929 Kahrilas, P. J., Logemann, J. A., Krugler, C., & Flanagan, E. (1991). Volitional augmentation of upper esophageal sphincter opening during swallowing. American Journal of Gastrointestinal and Liver Physiology, 260(3). Kahrilas, P. J., & Logemann, J. A. (1993). Volume accommodation during swallowing. Dysphagia, 8(3), 259–265. https://doi.org/10.1007/BF01​35​ 4548 Kahrilas, P. J., Lin, S., Chen, J., & Logemann, J. A. (1996). Oropharyngeal accommodation to swallow volume. Gastroenterology, 111(2), 297– 306. https://doi.org/10.1053/gast.1996.v111​ .pm8690194 Kaneda, H., Maeshima, K., Goto, N., Kobayakawa, T., Ayabe-Kanamura, S., & Saito, S. (2000).

Decline in taste and odor discrimination abilities with age, and relationship between gustation and olfaction. Chemical Senses, 25(3), 331–337. Kim, S., Doh, R., Yoo, L., Jeong, S., & Jung, B. (2021). Assessment of age-related changes on masticatory function in a population with normal dentition. International Journal of Environmental Research and Public Health, 18(13), 6899. https:// doi.org/10.3390/ijerph18136899 Knigge, M., Thibeault, S., & McColluch, T. (2014). Implementation of high-resolution manometry in the clinical practice of speech language pathology. Dysphagia, 29, 2–16. Lund, J. P., & Kolta, A. (2006). Generation of the central masticatory pattern and its modification by sensory feedback. Dysphagia, 21(3), 167–174. Mancopes, R., Gandhi, P., Smaoui, S., & Steele, C. M. (2021). Which physiological swallowing parameters change with healthy aging? OBM Geriatrics, 5(1). https://doi.org/10.21926/obm.geriatr​.2101153 Mandelstam, P., & Lieber, A. (1970). Cineradiographic evaluation of the esophagus in normal adults. A study of 146 subjects ranging in age from 21 to 90 years. Gastroenterology, 58(1), 32–39. Martin, B. J., Logemann, J. A., Shaker, R., & Dodds, W. J. (1994). Coordination between respiration and swallowing: Respiratory phase relationships and temporal integration. Journal of Applied Physiology, 76(2), 714–723. Miller, R., & Britton, D. (2011). Dysphagia in neuromuscular diseases. Plural Publishing. Morquette, P., Lavoie, R., Fhima, M. D., Lamoureux, X., Verdier, D., & Kolta, A. (2012). Generation of the masticatory central pattern and its modulation by sensory feedback. Progress in Neurobiology, 96(3), 340–355. https://doi.org/10.1016/j​ .pneurobio.2012.01.011 Newman, L., Cleveland, R., Blickman, J., Hillman, R., & Jaramillo, D. (1991). Videofluoroscopic analysis of the infant swallow. Investigative Radiology, 26(10), 870–873. Pauloski, B., & Nasir, S., (2016). Orosensory contributions to dysphagia: A link between perception of sweet and sour taste and pharyngeal delay time. Physiological Reports, 4(11). Preiksaitis, H. G., Mayrand, S., Robins, K., & Diamant, N. E. (1992). Coordination of respiration and swallowing: Effect of bolus volume in normal

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W. A. (1989). Respiratory patterns associated with swallowing: Part 2. Neurologically impaired dysphagic patients. Age and Ageing, 18(3), 173–176. Solemdal, K., Sandvik, L., Willumsen, T., Mowe, M., & Hummel, T. (2012). The impact of oral health on taste ability in acutely hospitalized elderly. PLOS ONE, 7(5), e36557. https://doi​ .org/​10.1371/journal.pone.0036557

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adults. American Journal of Physiology, 263(3 Pt 2), R624–R630. Ryu, J., Park, D., & Kang, J. (2015). Application and interpretation of high-resolution manometry for pharyngeal dysphagia. Journal of Neurogastroenterology and Motility, 21(2), 283–287. https:// doi.org/10.5056/15009 Selley, W. G., Flack, F. C., Ellis, R. E., & Brooks,

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➤ Learning Outcomes Upon completion of this chapter, students will be able to: n

Learn about the structures of the outer ear.

n

Review the muscles of the middle ear.

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Understand the landmarks of the middle ear cavity.

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Learn about the structures of the inner ear.

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Learn about the vestibulocochlear nerve.

➤ Structures of the Auditory Mechanism Researchers have been studying the auditory mechanism for centuries. In the 15th century, scientists discovered the presence of the eardrum and two of the three bones in the middle ear. Three hundred years later, Domenico Cotugno, an Italian physician, found that the middle ear was filled with air and the inner ear was filled with fluid. Later, Ernst Reissner, the German anatomist, noted that there were two fluid compartments in the cochlea (an inner ear structure of hearing). During the 19th century, Alfonso Corti, the Italian physician, described cells that made up the sensory receptor organ of the inner ear. In the period between 1877 and 1900, many inventions helped with enhancing the role of hearing in everyday activities and changed the course of history. Thomas Edison, Alexander Graham Bell, Nikola Tesla, and Guglielmo Marconi provided the world with the phonograph, telephone, and radio, respectively. The fascination with sound led Hermann von Helmholtz and Georg von Békésy to describe how mechanical energy was converted to electrical signals in the brain. The pioneering work of von Békésy eventually led to him winning the 1961 Nobel Prize in Medicine and Physiology (Brownell, 1997). Since that time, there have been major strides in our understanding of hearing and the anatomy of the hearing mechanism. 315

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We often take hearing for granted; however, it is a complex process as some of the smallest structures in the human body are located in the ear. Hearing is the only sensory system that allows us to understand things that happen in our environment. For example, if a baby cries in a dark room, we can hear the baby cry but do not need to see the baby to know of its presence. This ability to hear sounds is often deemed crucial to the development of oral communication; therefore, it is essential for speech-language pathology and audiology students to understand the anatomy of the auditory system. Students need to know how these structures work together to transform sound waves into sounds that we recognize and understand. Ultimately, the language that we use to communicate is often influenced by what we hear. Conversely, damage or dysfunction of certain structures of hearing may impact communication.

➤ Outer Ear The earlobes increase in size until about 8 to 10 years of age (Niemitz et al., 2007). It appears that throughout a person’s life, the earlobes never stop growing, but with age the earlobes begin to droop because gravity actually pulls down the cartilages of the earlobes that are made up of collagen and other fibers. Your ears also never stop hearing. Even during sleep, the ears do not stop hearing; however, the brain processes sound differently than when you are awake. The two major structures of the outer ear are the auricle and the external auditory meatus. At the end of the external auditory meatus is the tympanic membrane.

Auricle The auricle, also known as the pinna (Figure 9–1), is the visible, prominent portion of the outer ear. It is composed of cartilage (auricular cartilage) and rests on the side of the head at approximately a 30° angle (Naumann, 2007). There are arteries, veins, and nerves within the pinna. The cartilage of the pinna is also coated in hairs and sebaceous glands, which serve to keep dirt and other harmful substances from entering the ear canal (Brownell, 1997): n

The pinna is shaped like a funnel and has various grooves and folds, so it serves to localize and collect sound and guide it into the ear canal. The depressions and the eminences in the pinna help in increasing the surface area of the pinna and contribute toward amplification of sound entering the ear canal. The deepest of these grooves is known as the concha; it is the entry point of the ear canal and it allows for directing sound to the external acoustic meatus (crescentshaped passageway that runs from the concha to the tympanic membrane). The upper portion of the concha is the cymba conchae (Figure 9–1), while the lower portion is the cavum conchae (Figure 9–1).

n The

antihelix (Figure 9–1) is the ridge that defines the concha boundary; it is semicircular in shape. The superior portion of the antihelix divides above to form two crura (legs) — the crura antihelicis (helical crura) (Figure 9–1) between which lies a triangular depression known as the triangular fossa (or fossa triangularis) (Figure 9–1). The antihelix is parallel with and anterior to the helix (Figure 9–1), which is the outermost ridge of the pinna. The helix defines the shape of the outer ear: n

A thickened protuberance frequently found on the superior and posterior portion of the helix is the auricular (or Darwin) tubercle (Figure 9–1). Charles Darwin first discussed it as a vestigial feature to denote common ancestry among primates whose ears were pointy. The scaphoid fossa (Figure 9–1) is the depression between the helix and antihelix. 316

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FIGURE 9–1.  Anatomy of the pinna. Source: Figure 12.2 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 505), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

n The

tragus (Figure 9–1) is a flap of cartilage anterior to the concha that partially occludes the entrance to the ear canal (Kaushal & Kaushal, 2011). The inferior margin of the concha opposite to the tragus is the antitragus (Figure 9–1). The space between the tragus and antitragus is known as the intertragal incisure. n The most inferior portion of the pinna is the earlobe (lobule or earflap) (Figure 9–1). It is composed of connective tissue and is not firm, unlike the elastic portions of the outer ear (Kaushal & Kaushal, 2011). The lobe may be connected to (attached) or disconnected from the side of the head (free).

Auricular Cartilage The auricular cartilage is a continuous piece of fibrocartilage covered in skin. Ligaments and muscles connect the cartilage to adjacent parts of the ear. The cartilage helps to maintain the shape of the ear and is the outermost part of the ear. It has no nerve cells or blood vessels (Mark, 1982).

Auricular Muscles Extrinsic auricular muscles connect the pinna to the side of the head, while intrinsic muscles connect structures of the pinna to each other. These muscles serve no major function in humans and are considered vestigial (Liugan et al., 2018). These muscles are innervated by the temporal (superior auricular muscle and anterior auricular muscle) and posterior auricular muscle branches of cranial nerve VII (facial nerve) (Liugan et al., 2018; Sataloff & Selber, 2003). These muscles receive vascularization from the superficial temporal, posterior auricular, and occipital arteries (Hoogbergen et al., 1996): 317

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n The

extrinsic auricular muscles include the

n

superior auricular muscle, which is the largest of the three muscles

n

anterior auricular muscle, which is the smallest of the three muscles

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posterior auricular muscle, which is made up of a couple of fleshy fasciculi

n The n

n n

intrinsic auricular muscles include the

antitragicus (antitragus), which modifies the shape of the ear when it pulls the cauda helicis and antitragus toward each other helicis minor, which modifies the shape of the anterior portion of the ear cartilage helicis major (large muscle of the helix), which modifies the shape of the ear by lowering the anterior margin of the ear cartilage

n

obliquus auriculae, which is located on the cranial surface of the pinna

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tragicus, which may assist with opening the external acoustic meatus

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transversus auriculae, which helps to flatten the auricular cartilage

Auricular Ligaments Three extrinsic auricular ligaments attach the auricle to the side of the head: n The

anterior auricular ligament courses from the root of the zygomatic process and inserts into the spine of the helix.

n The

posterior auricular ligament courses from the mastoid process and inserts into the conchal eminence.

n The

superior auricular ligament courses from the superior margin of the osseous external acoustic meatus and inserts into the spine of the helix.

The intrinsic auricular ligaments connect structures of the auricle to each other: n

These are a band of strong fibers that course from the tragus to the helix.

n

These are located between the cauda helicis and the antihelix.

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Some fibers are located on the cranial surface of the auricle.

External Auditory Meatus The external auditory meatus (EAM), also known as the ear canal or auditory canal (Figure 9–2), is a 2.5-cm long, S-shaped tube that extends from the concha to the tympanic membrane. Its diameter is about 7 mm (Faddis, 2007). The EAM courses downward so that water, dirt, and other foreign substances do not build up within the canal. The EAM is innervated by the auriculotemporal branch of the mandibular nerve (CN V) and branches of the facial nerve (CN VII) and vagus nerve (CN X). The auriculotemporal nerve provides sensory innervation to the anterior and superior walls of the EAM, while the auricular branch of the vagus and facial nerve supplies innervation to the posterior and inferior walls. The outer one third of the EAM is composed of cartilage; the remaining two thirds are the boney (or osseous) portion of the ear canal in the temporal bone. The first one third is lined with skin, small hairs (cilia), and sebaceous and ceruminous glands. These glands produce cerumen (earwax), which protects the EAM from foreign substances and prevents it from drying out. The cerumen helps with lubrication 318

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FIGURE 9–2. External auditory meatus and eardrum. Source: Figure 12.1 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 504), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

and provides protection from fungi and bacteria. If there is an excessive amount of cerumen, it can occlude the EAM or push against the eardrum and may result in a conductive hearing loss. The cilia also serve to protect the EAM from foreign bodies. The bony (or osseous) portion is also lined with skin and is narrower than the cartilaginous portion (Alvord & Farmer, 1997). The EAM has two major constrictions: n

The first is known as the auricular, or external, orifice. It is located at the inner end of the first one third of the ear canal (the cartilaginous portion); this is where the diameter of the EAM is the largest.

n

The diameter gradually decreases to form the second constriction, known as the isthmus, which is where the cartilaginous portion meets the bony portion of the EAM.

Because the EAM is open at one end (the concha) and closed at the other (the tympanic membrane or eardrum) (Figure 9–2), it has its own resonant frequency, which can amplify an incoming frequency of 2500 Hz by up to 20 dB (Menezes et al., 2004).

Tympanic Membrane The tympanic membrane, or eardrum (Figure 9–3), is the boundary between the outer and middle ear and is placed at an approximate 55° angle at the end of the EAM (the terms tympanic membrane and eardrum are used interchangeably throughout this text). It resides in a bony groove in the temporal bone of the EAM known as the tympanic, or annular, sulcus. The tympanic membrane is thin, concave, 319

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FIGURE 9–3.  Tympanic membrane.

semitransparent, and pearl-gray in color. Its outer periphery is a thickened fibrocartilaginous annulus (ring) that fits in the tympanic sulcus. The eardrum is about 10 mm in superior-inferior diameter; its height is slightly longer than its width due to its concavity. Though it is thin, the tympanic membrane is tough and relatively resistant to rupturing. It is the only membrane in the body that is surrounded by air on both sides (Luers & Hüttenbrink, 2015). The Sama-Baju people from Malaysia and Indonesia are known for their free diving (breath-holding underwater) abilities. Some have been known to dive for more than 5 hr a day and stay submerged for long periods. Early in life, they purposely rupture their eardrums so that they can stay underwater for an extended time. Pressure in the eardrum, therefore, does not equalize, and later in life, many become hard of hearing (Langenheim, 2010). The tympanic membrane is composed of three layers of tissue: n

The outermost layer, the cuticular layer, is a thin epithelial lining that is continuous with the epithelium of the outer ear.

n

The middle layer, known as the intermediate (fibrous) layer, is composed of two layers of fibers that give the eardrum its compliance and sturdiness: n

n

The superior region of this layer is the pars flaccida (Figure 9–3); it is less fibrous and moves outward for pressure equalization in the middle ear (Sadé, 1997). The remaining, more fibrous and tense, portion of the intermediate layer is the pars tensa (Figure 9–3), which moves inward (Sadé, 1997). The anterior and posterior malleolar folds are on either side of the pars flaccida and separate the pars flaccida from the pars tensa. 320

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The innermost layer of the tympanic membrane, known as the mucous layer, is a mucous membrane that is continuous with the mucosal lining of the rest of the middle ear.

The tympanic membrane is concave. The deepest, most depressed part is known as the umbo (Figure 9–3). One of the ossicles of the middle ear, the malleus, attaches to the tympanic membrane at this point. The cone of light (Figure 9–3) also radiates from the umbo. The cone of light is the reflection of otoscope light that is created due to the concavity of the tympanic membrane (Gelfand, 2016). The cone of light is used as a diagnostic sign of a healthy eardrum and middle ear because it will be absent if the middle ear is unable to properly ventilate and the eardrum is displaced inward.

Clinical Note A perforated eardrum — a hole or tear in the eardrum — can be the result of inflammatory diseases, such as otitis media, barotrauma (rupture due to imbalance between the air pressure in the middle ear and the environment), loud sounds, or trauma from foreign objects. Those experiencing a perforated eardrum will likely experience conductive hearing loss and possibly tinnitus (ringing in the ears), bleeding, and vertigo (sensation of spinning while stationary). Although most people will recover completely without intervention in a few weeks, in some rare cases, surgical intervention, such as tympanoplasty, may be necessary.

➤ Middle Ear The middle ear space is an irregularly shaped, air-filled cavity in the petrous portion of the temporal bone. It is approximately 2 to 4 mm wide and is about 15 mm in vertical dimension, creating a volume of approximately 2 cm3. The middle ear cavity is enclosed by bone on all margins except for its lateral wall, which is the site of the tympanic membrane (Luers & Hüttenbrink, 2015).

Ossicles Three ossicles (bones) are connected to the tympanic membrane. These bones, the malleus, incus, and stapes, occupy most of the middle ear space and are the smallest bones in the body (Kamrava & Roehm, 2017). These three bones together are commonly referred to as the ossicular chain. Vibrations are transmitted from the tympanic membrane through the ossicles to the inner ear.

Malleus The first and largest of the ossicles is the malleus (Figure 9–4). It is attached to the tympanic membrane via fibers of connective tissue. Its shape is similar to that of a hammer, and it is approximately 9 mm long (Todd & Creighton, 2013). The malleus has several parts — a head, neck, and three processes. The majority of the malleus is the head (or caput), and it is the point of articulation with the second ossicle, the incus, creating the incudomalleolar joint in a space known as the epitympanic recess. The neck is narrow and just below the head. Three projections (or processes) — the manubrium, anterior process, and lateral process, are attached to the neck: 321

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FIGURE 9–4. Ossicles, muscles, and boundaries of the middle ear. Source: Figure 12.3 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 506), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

n The

manubrium (or handle) is the long, vertical process of the malleus just behind the tympanic membrane. The manubrium can actually be seen behind the eardrum; it looks like an opaque streak, known as the malleolar stria. The attachment point for the tensor tympani muscle is located where the manubrium meets the neck of the malleus.

n

Ligaments attach to the anterior and lateral processes, named for the directions they project. The lateral process is the attachment point of the manubrium to the tympanic membrane; this point, known as the malleolar prominence, forms the malleolar folds and pars flaccida.

Incus The second ossicle, the incus (Figure 9–4), is shaped like an anvil and is about 7 mm long. It has a body and two crura (arms or processes) that meet at approximate right angles: n The

short process is about 5 mm long and projects backward (Noussios et al., 2016).

n The

long process is about 7 mm long and projects vertically — nearly parallel with the manubrium of the malleus. The bottom of the long process bends medially to form a projection, known as the lenticular process; the head of the stapes articulates with the incus at this point. The articulation of the incus with the malleus at the incudomalleolar

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joint causes them to move together as a unit rather than individually (Burford & Mason, 2016).

Stapes The smallest ossicle, the stapes (Figure 9–4), is shaped like a stirrup with an approximate area of 3.5 mm2 (Noussios et al., 2016). It is the smallest and lightest bone in the body. It is composed of several parts — a head, neck, two crura, and a footplate. The stapes connects and transmits sound vibrations to the oval window of the inner ear: n The

head of the stapes meets the incus at the lenticular process; this articulation forms a balland-socket joint, called the incudostapedial joint.

n The

neck is the constriction between the head and base of the crura of the stapes. The stapedius muscle inserts at the neck.

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The two crura (anterior and posterior) split from the neck and connect together at the footplate, which is a flattened piece that is shaped like an oval. The footplate of the stapes resides in the oval window (Luers & Hüttenbrink, 2015).

Clinical Note Otosclerosis is a disease in which the stapes becomes fixed in the oval window. This interferes with the conduction of sound through the ossicles to the inner ear and results in a conductive hearing loss. Otosclerosis can be congenital (present at birth), hereditary, or viral (environmental). It is more likely to occur in younger individuals and females. There are two common treatments for otosclerosis — stapedectomy, surgery to remove the stapes and replace it with a prosthetic stapes, and stapedotomy, in which a prosthesis is placed in a small hole that is made in the base of the stapes.

Ossicular Ligaments Six ligaments and two tendons hold and balance the ossicular chain within the middle ear, allowing them to work together to conduct sound through the middle ear to the inner ear: n

The head of the malleus is held in the epitympanic recess by its superior ligament.

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The neck of the malleus is connected to the anterior wall of the middle ear cavity by its anterior ligament.

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The head of the malleus is bound to the lateral wall by its lateral ligament. The malleus is also suspended by the tendon of the tensor tympani muscle.

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The short process of the incus is suspended by its posterior ligament.

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The incus also has a superior ligament, which attaches it to the epitympanic recess.

n The

annular ligament holds the footplate of the stapes in the oval window. The tendon of the stapedius muscle also holds the stapes in place.

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Clinical Note While the acoustic reflex of the contraction of the tensor tympani and stapedius muscles dampens the acoustic signal of lower frequencies, it does not protect the inner ear from higher frequency sounds. This lack of protection from higher frequencies can account for the common occurrence of hearing loss caused by high frequency sounds, such as the frequencies of loud music or exposure to high frequencies while working in industrial occupations.

Muscles of the Middle Ear Two striated (voluntary) muscles connect to the ossicles of the middle ear: stapedius (Figure 9–4) and tensor tympani (Figure 9–4). Like the ossicles they attach to, these muscles are both very small. The stapedius is the smallest muscle in the body. Both the stapedius and tensor tympani muscles do not reside in the tympanic cavity (Prasad et al., 2019); they are housed in the bony canals, while their tendons are in the middle ear cavity. Together, these muscles stiffen the ossicular chain; this action is known as the acoustic reflex that mainly protects against low-frequency sounds. The first time the acoustic reflex in humans was noted was by Luscher in 1929. The acoustic reflex, also known as the middle ear–muscles (MEM) reflex, diminishes the admittance of lower frequency signals and is believed to protect the cochlea because it inhibits excessive vibration of the stapes in the oval window (Mukerji et al., 2010).

Stapedius The stapedius muscle is about 1 mm in length (Rodríguez-Vázquez, 2009). It originates from a pinpoint foramen in the apex of the pyramidal eminence; its tendon’s point of insertion is the neck of the stapes. The muscle runs vertically, but its tendon runs horizontally. The stapedial branch of the facial nerve (CN VII) innervates the stapedius muscle. When presented with loud sounds, the stapedius muscle contracts to turn the stapes posteriorly. Hypersensitivity to loud noises (hyperacusis) may be caused by paralysis of the stapedius muscle.

Tensor Tympani The tensor tympani muscle is larger than the stapedius; it is approximately 25 mm long with a crosssectional area of approximately 5.85 cm2 (Aristeguieta et al., 2009). In addition to containing striated muscle, smooth muscle fascia has been found within the tensor tympani muscle, indicating that it may have both voluntary and involuntary (parasympathetic) control. Its point of origin is from the cartilage of the auditory tube and from the sphenoid bone. The tendon of this muscle connects to the neck of the malleus. This tendon enters the middle ear cavity from the anterior wall. The trigeminal nerve (CN V) innervates the tensor tympani muscle. When contracted, the stapedius and tensor tympani muscles exert forces in opposite directions. When the tensor tympani muscle is contracted, it moves the malleus in a medial and anterior direction to increase the tension of the eardrum and reduce its range of motion. To dampen vibrations during mastication (chewing) and swallowing, the tensor tympani acts alongside the tensor veli palatini to increase tension on the malleolus, which increases tension in the eardrum (Szymanski & Agarwal, 2018).

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Landmarks of the Middle Ear Cavity Medial Wall The medial wall of the middle ear space, also known as the labyrinthian or labyrinthine wall, houses structures associated with the inner ear, including the oval window, round window, promontory, and the prominence of the lateral semicircular canal: n The

oval window (Figure 9–4) (also known as fenestra vestibuli or fenestra ovalis) is the boundary between the air-filled middle ear and the fluid-filled vestibule of the inner ear. The footplate of the stapes resides in the superior and posterior part of the oval window.

n The

round window (Figure 9–4) (also known as fenestra cochlea or fenestra rotunda) is covered by a thin, flexible membrane, called the secondary tympanic membrane. It is the boundary between the middle ear and the scala tympani of the cochlea (a structure of the inner ear) and is positioned below the oval window.

n The

promontory is located between the oval window and the round window. It is a rounded protuberance shaped by the basal turn of the cochlea on the other side of the middle ear space.

n The

lateral semicircular canal (a structure of the vestibular system of the inner ear) forms a small prominence that is visible on the medial wall of the middle ear space. This prominence is located just above the oval window.

Clinical Note The eustachian tube is shorter and more horizontal in children than in adults; it grows and changes position as the head grows. This accounts for the higher frequency of middle ear infections (otitis media) in young children. As a result of this shorter and more horizontal eustachian tube, fluid from the middle ear may be unable to readily drain from the middle ear space into the nasopharynx. Secretions from the nasal cavity may also flow into the eustachian tube. The middle ear, therefore, will not be efficiently aerated and will impact the ability of the eardrum to vibrate optimally.

Anterior Wall The anterior wall, also known as the carotid wall, is narrower at the bottom than it is at the top and contains the orifice (opening) of the eustachian tube (auditory tube, pharyngotympanic tube) (Figure 9–4). The internal carotid artery runs within this wall through the carotid canal. The eustachian tube courses parallel to the tensor tympani muscle at an approximate 45° angle from the horizontal plane; the orifice of the eustachian tube is separated from the tensor tympani muscle by a curved bone known as the cochleariform process. The eustachian tube is approximately 36 mm long and connects the nasopharynx to the middle ear (Szymanski & Agarwal, 2018). The first one third (about 12 mm) of the eustachian tube is composed of bone, and the final two thirds (about 18 to 24 mm, coursing to the nasopharynx) is made of cartilage. At the juncture of bone and cartilage, the eustachian tube narrows; this region is known as the isthmus.

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The eustachian tube serves to aerate (bring oxygen to) the middle ear. The cartilage of the eustachian tube is collapsed and closed at rest; it is opened by the contraction of the tensor veli palatini and levator veli palatini muscles. When the eustachian tube opens, atmospheric air enters the middle ear cavity to equalize the air pressure within the middle ear and the atmospheric pressure within the ear canal. The eustachian tube normally opens when talking, yawning, chewing, and swallowing (Swarts et al., 2011). Because of its connection to the nasopharynx, the eustachian tube also serves to drain fluid from the middle ear into the nasopharynx.

Clinical Note If an infection in the middle ear cavity is severe, it can cause an abscess in the superior wall that can invade the cranial space and spread to the meninges of the brain. If untreated, the spreading of this infection can cause a brain abscess.

Posterior Wall The posterior (or mastoid) wall is wider at the top than at the bottom. The opening of the antrum, called the aditus, arises from this wall near the epitympanic recess. The antrum is the passageway that is directed to the mastoid process of the temporal bone. The air from the tympanic cavity travels through the antrum to the air cells of the mastoid process. The tendon of the stapedius muscle emerges from the pyramidal eminence along the posterior wall before connecting with the neck of the stapes. A branch of the facial nerve, the chorda tympani (Figure 9–4), travels within the posterior wall.

Floor The floor of the middle ear cavity is also called the inferior wall or jugular wall. It is a narrow plate of the tympanic bone. The floor divides the middle ear space and the jugular fossa, which houses the jugular vein (Figure 9–4).

Superior Wall The superior wall, also known as the roof or tegmental wall, is composed of a thin plate of bone that serves to divide the cranial space from the tympanic cavity.

➤ Inner Ear The inner ear, also called the labyrinth, is located in the petrous part of the temporal bone deep within the skull. It consists of structures relating to two systems — the auditory system and vestibular system. Structurally, the labyrinth consists of two main parts. All the structures of the inner ear are contained within an osseous (bony) labyrinth; within this bony labyrinth is a membranous labyrinth (lined with epithelium). The bony labyrinth contains the cochlea vestibule and osseous semicircular canals (Figure 9–5). Each of these three canals connects to the vestibule of the inner ear at a bulblike dilation known as an ampulla (Figure 9–5). The membranous labyrinth is composed of the cochlear duct (scala media), utricle, saccule, and membranous semicircular canals (Figure 9–5). 326

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FIGURE 9–5.  Inner ear. Source: Figure 12.7 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 510), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

This chapter organizes structures based on system (auditory and vestibular) rather than by location of structures (osseous labyrinth versus membranous labyrinth) because it will facilitate a better understanding of the physiology of these structures discussed later in this book. Additionally, the acoustic nerve (CN VIII) receives sensation from both the auditory and vestibular system and transmits this information to the brain (Figure 9–5) (Atkinson et al., 2015).

Auditory System:  Cochlea and Related Structures The cochlea was first described by Eustachi in 1564. The cochlea (or osseous cochlear labyrinth) is located in the medial portion of the osseous (bony) labyrinth. It derives its name from cochlos, the Greek word for “snail,” because of its resemblance in shape to the coiling of a snail’s shell. The cochlea is about 9 mm wide at its base and coils around about 2½ times to reach its apex, which is narrower and points forward, outward, and slightly downward. The cochlea is about 35 mm long and is about 5 mm in length from the base to the apex (Rask-Anderson et al., 2012). The cochlea is very small — about the size of a pea. There are over 20,000 hair cells in the cochlea. The outer hair cells (OHCs) in the cochlea mechanically augment low-level sounds, and the inner hair cells (IHCs) convert sound vibrations in the cochlear fluids to electric signals that are transmitted to the auditory brainstem and the auditory cortex by the auditory nerve.

Vestibule Originating from the Latin word vestibulum (“entrance hall”), the vestibule is the oval-shaped entrance to the cochlea, and it is the shared, central cavity for the structures of the inner ear, including the 327

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vestibular system. It is about 3 mm wide and 5 mm in the anterior-posterior dimension (Hou & Wang, 2013). The lateral wall of the vestibule contains the oval window (Figure 9–6). There are three recesses (depressions) within the vestibule — the spherical, cochlear, and elliptical recesses — allowing communication between parts of the inner ear.

Modiolus The central core around which the cochlea coils is a bone known as the modiolus. It has a wide base and is situated at the bottom of the internal auditory meatus (or canal) of the temporal bone, which CN VIII travels through. The modiolus has tiny perforations through which blood vessels and nerve fibers of CN VIII pass. It serves to protect these vessels and fibers. The modiolus also houses the spiral ganglion, a collection of neurons whose axons extend into CN VIII and send sound impulses from the cochlea to the brain.

Osseous Spiral Lamina The osseous spiral lamina is formed by two bony plates that extend outward from the modiolus. The space between these two plates is known as the habenula perforata; nerve fibers travel through here. The scala media (Figure 9–6) attaches to the spiral lamina. The osseous spiral lamina gradually becomes smaller toward its apex. Following the shape of the cochlea, the spiral lamina coils about 2½ times (Brownell, 1997) around the modiolus and splits the cochlea into two different passageways: scala vestibuli (Figure 9–6) and scala tympani (Figure 9–6).

FIGURE 9–6.  Cochlea and related structures. Source: Figure 12.5 from Advance Review of SpeechLanguage Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 509), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

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The upper passageway (or duct) begins at the oval window and is known as the scala vestibuli; the oval window allows communication between the scala vestibuli and the middle ear. The lower passageway is known as the scala tympani. The scala tympani ends at the round window (Figure 9–6), which allows communication between the scala tympani and the middle ear. The cochlear aqueduct is a small opening near the round window between the scala tympani and the cranial cavity. At the hookshaped apex (hamulus) of the two chambers of the spiral lamina is a small opening called the helicotrema (Figure 9–6); the scala vestibuli and scala tympani communicate at this point. The scala tympani and scala vestibuli are filled with a clear fluid, called perilymph (Figure 9–6). The helicotrema allows perilymph to flow between them. The composition of perilymph is high in sodium (Na+) and calcium (Ca++), and it is low in potassium (K+) (Gagov et al., 2018). Perilymph is also found in the perilymphatic space, which is the space between the wall of the bony labyrinth and the membranous labyrinth of the vestibular system.

Scala Media The scala media, or cochlear duct (Figure 9–6), is part of the membranous labyrinth within the osseous labyrinth of the inner ear (the remaining structures of the membranous labyrinth are part of the vestibular system). The scala media resides inside the cochlea on the osseous spiral lamina, and like the cochlea, it is spiral in shape. The scala media is about 25 to 35 mm long when it is uncoiled (Dhanasingh, 2019). The scala media is located between the scala vestibuli and scala tympani, creating the division between the two passageways. Unlike the scala vestibuli and scala tympani, which are filled with perilymph, the scala media is filled with a fluid called endolymph (Figure 9–6). Endolymph has a larger concentration of potassium (K+) than sodium (Na+) and calcium (Ca++) (Gagov et al., 2018). Reissner membrane (vestibular membrane) (Figure 9–6) named after the German anatomist Ernst Reissner, is a thin, epithelium-lined membrane that forms the roof of the scala media and thus separates the scala vestibuli from the scala media. The floor of the scala media is formed by a thin, fibrous membrane known as the basilar membrane (or cochlear partition) (Figure 9–6); it separates the scala media from the scala tympani. The basilar membrane is wider at its apex and narrower at its base; therefore, it is tenser at the base and more flaccid at the apex. The spiral ligament attaches the basilar membrane to the lateral wall of the osseous spiral lamina. The stria vascularis is a layer of vascular epithelium attached to the spiral ligament that spans from Reissner membrane to the basilar membrane along the lateral wall of the scala media. The stria vascularis is made up of columnar and cuboidal cells, known as the cells of Claudius and Boettcher (Figure 9–7), respectively; it supplies potassium ions to the endolymph of the scala media. The organ of Corti (Figure 9–7), first described by Italian anatomist Alfonso Corti in 1851, is also known as the spiral organ. It rests on the basilar membrane within the scala media. It is the essential organ of hearing in the inner ear because it is responsible for transduction — the transformation of mechanical energy from the middle ear into neural impulses. The organ of Corti contains two types of sensory cells (the IHCs and OHCs) and several kinds of supporting cells: n

The cells of Claudius and Boettcher that are made up of the stria vascularis are considered supporting cells. n Another type of supporting cell, known as pillar cells, forms the tunnel of Corti (Figure 9–7), which separates the singular row of inner hair cells from the three rows of outer hair cells. The tunnel of Corti contains fluid, known as cortilymph. The broad base of the pillar cells is also embedded in the basilar membrane. There are approximately 3,500 IHCs in a singular row on

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FIGURE 9–7.  Organ of Corti and related structures. Source: Figure 12.6 from Advance Review of SpeechLanguage Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 510), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

the modiolar (medial) side of the organ of Corti (Gelfand, 2016). The IHCs are broader at the base and have a narrow neck, resembling a teardrop in shape. Phalangeal cells support their bases. On the lateral side of the organ of Corti are about 12,000 to 13,500 cylindrical-shaped OHCs arranged in three rows (Gelfand, 2016). The length of the OHCs is dependent upon where it sits along the basilar membrane — the hair cells are longer at the apex of the basilar membrane and are shorter at the base. They sit on a base of supporting cells, known as Deiters cells (Figure 9–7) (named after German neuroanatomist Otto Deiters), which are embedded in the basilar membrane. Immediately adjacent to the final row of Deiters’ cells are five to six rows of Hensen cells (Figure 9–7) that are named after German anatomist and physiologist Victor Hensen; these column-shaped cells also support the OHCs as well as the tectorial membrane. The sensory hairs on both the IHCs and OHCs are known as stereocilia (used interchangeably with cilia). Approximately 50 stereocilia are arranged in a U-shaped pattern on each IHC, while about 65 to 150 stereocilia clump in W and V shapes on each OHC (Gelfand, 2016). The stereocilia are, for both the IHCs and OHCs, longer and less in number at the apex of the cochlea than the base. The stereocilia project through a fragile reticular membrane (or lamina) (Figure 9–7) made of phalangeal cells (Deiters cells). The bottom (basal) end of the hair cells connects to nerve fibers of CN VIII.

Clinical Note Noise-induced hearing loss is the result of exposure to extreme sound levels, such as loud live music or industrial work. The OHCs are vulnerable to damage from excessive sounds; this damage limits the inner ear’s ability to function properly. Once they are damaged, OHCs are unable to regenerate. It is important, therefore, to educate clients about the importance of wearing earplugs in situations where they may be exposed to loud sounds.

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The tectorial membrane (Figure 9–7) originates from the spiral limbus, a collection of connective tissue that lies on the spiral lamina and connects to Reissner membrane. The tectorial membrane rests on top of the cilia of the hair cells; it consists of protein and collagen (Fettiplace & Kim, 2014). The space between the tectorial membrane and the basilar membrane is filled with endolymph. The tectorial membrane serves to provide the shearing force on the cilia of the OHCs, which are embedded in it. The IHCs do not come in contact with the tectorial membrane, though they are within close vicinity. The IHCs and OHCs are both innervated via afferent and efferent fibers: n

The afferent fibers arise from CN VIII (vestibulocochlear nerve). Type I fibers are large, coated in myelin, and are responsible for innervating the IHCs. Type II fibers are smaller, can be myelinated or unmyelinated, and are responsible for the innervation of the OHCs. A single IHC can be attached to up to 10 CN VIII fibers, while a single CN VIII fiber can innervate up to 10 OHCs (Atkinson et al., 2015).

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The efferent innervation serves an inhibitory function in opposition to afferent stimulation of the hair cells. The efferent pathway is part of the olivary complex of the brainstem.

Vestibular System The vestibular system is responsible for sending sensory information regarding balance and equilibrium to the brain. Structures from both the bony labyrinth and membranous labyrinth are part of the vestibular system (Angelaki & Cullen, 2008).

Osseous Semicircular Canals There are three osseous semicircular canals spatially arranged based on their anatomical orientation — ​ anterior (or superior), posterior, and lateral (or horizontal); as the name suggests, they are part of the bony labyrinth of the inner ear. The canals reside above and behind the vestibule of the inner ear. They resemble rings and are positioned perpendicularly at 90° angles of each other. The positioning of the canals in relation to each other is key to the brain’s ability to code movements of the head at different angles. Each of these three canals joins the vestibule of the inner ear at a bulblike dilation known as an ampulla (plural ampullae). Each ampulla is about two times the diameter of its corresponding canal. In each ampulla is a crista ampularis, the sensory organ for movement; the hair cells of this organ are ciliated. There are approximately 6,000 to 8,000 vestibular hair cells in the crista ampularis, with the number decreasing with increased age (Lopez et al., 2005). Each of these hair cells has about 50 stereocilia and one kinocilium, the sensory receptor of the hair cell (Raphael & Altschuler, 2003). A gelatinous cap, known as the cupola (or cupula), lies on top of the cilia; the stereocilia and kinocilium are embedded in it: n The

anterior (or superior) semicircular canal is positioned vertically and perpendicularly to the temporal bone’s long axis. It resembles two thirds of a ring and contains the ampulla anteriorly, while the opposite, nondilated end combines with the analogous part of the posterior canal, creating the crus commune — an opening into the upper, internal portion of the vestibule.

n The

posterior semicircular canal is the longest of the three semicircular canals. It is also positioned vertically, but it is parallel to the temporal bone’s long axis. The posterior lower portion of the canal opens up to its ampulla. The opposite end of the canal meets the anterior canal at the crus commune.

n The

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(Spasic et al., 2015). The ampullated end of the canal is located near the ampullated end of the anterior canal, just above the oval window.

Membranous Labyrinth The membranous labyrinth of the inner ear is filled with endolymph and is fixed within the osseous labyrinth. While the scala media is the part of the membranous labyrinth responsible for hearing, there are components of the membranous labyrinth that serve the vestibular system. These components are the n utricle n saccule n

membranous semicircular canals

The utricle and saccule are vestibular structures located within the vestibule of the inner ear and are innervated by the vestibular branch of CN VIII. The saccule resides on the medial wall of the membranous labyrinth and connects to the cochlea through the ductus reuniens. The utricle is located within the elliptical recess of the vestibule; it is bigger and connects to the membranous semicircular canals through five openings. The elliptical recess allows communication between the utricle and the ampullae of the superior and lateral semicircular canals. The utricle and saccule connect indirectly via the endolymphatic duct, and both have a sensory organ, known as the macula (plural maculae). The maculae are composed of epithelium, 40 to 70 stereocilia, a single kinocilium, and a gelatinous cap (the cupola) (Spasic et al., 2015). The two maculae are positioned perpendicularly to each other. Both the utricle and saccule have an overlying otolithic membrane, which has deposits of calcium carbonate, called otoliths, embedded in it; these otoliths press against the hair cells.

Clinical Note Otoliths are able to sense gravity and linear acceleration that occur in a straight line. Damage to these organs will result in problems with orientation to gravity and the ability to sense motion. The membranous semicircular canals connect to the utricle in the vestibule of the inner ear via five openings, or orifices. These canals are located within the osseous semicircular canals, so they are alike in shape but are approximately one third smaller in diameter. The membranous canals also join the vestibule of the inner ear at the bulblike membranous ampullae, which are housed within the osseous ampullae.

Vestibulocochlear Nerve (CN VIII) The eighth cranial nerve is commonly referred to by several names, including the auditory, acoustic, vestibulocochlear, or auditory vestibular nerve. The main trunk of CN VIII travels through the internal auditory meatus (canal). It is at the bottom of this canal that the nerve splits into its two branches. It is a sensory (or afferent) cranial nerve composed of two branches — cochlear and vestibular : n

The cochlear branch (or cochlear nerve) originates at the spiral ganglion and sends sensory information regarding sound to the brain. Its central fibers travel through the modiolus of the

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inner ear and into the internal auditory meatus. The cochlear branch also has peripheral fibers, which travel to the hair cells in the cochlea. The fibers of the cochlear branch terminate in ventral and dorsal cochlear nuclei, pass through other structures of the nervous system (trapezoid bodies, lateral lemniscus, and medial geniculate bodies), and extend to the auditory cortex of the temporal lobe of the brain.

Clinical Note Damage to the vestibulocochlear nerve may result in motion sickness, vomiting, hearing loss, a false sense of motion, loss of balance in dark places, vertigo, nystagmus, gaze-evoked tinnitus, or ringing in the ears. n

The vestibular branch (or vestibular nerve) originates from the vestibular ganglion, located within the internal auditory meatus, and sends sensory information regarding equilibrium, movement, and balance to the brain (Sanders & Gillig, 2010). It has three peripheral fibers that occupy the utricle, ampullae, and saccule of the vestibular system. The central fibers of the vestibular branch travel along the same path as the cochlear nerve and end at the vestibular nucleus in the pons and medulla of the brain. Some central fibers travel to the cerebellum. Vestibular fibers are made up of critical reflex pathways.

➤ Changes With Age (Presbycusis) Presbycusis is the term for the acquired hearing disorder that results from the changes that accompany normal aging (Van Eyken et al., 2007). As individuals age, structures of the outer, middle, and inner ear change. The pinna becomes drier, and its tissue loses elasticity. In males, more hair may grow in the grooves of the pinna. The epithelium of the EAM also becomes drier. While these changes impact the outward appearance of the outer ear, they do not directly impact an individual’s hearing. In the middle ear, muscles and tendons weaken with age. The tympanic membrane and the joints between the ossicles may become less elastic. The ossicular chain becomes more rigid. These changes in the middle ear may have a minor negative impact on the conduction of vibrations through the middle ear. Most of the changes that cause presbycusis occur in the inner ear. Starting at the base of the cochlea, hair cells and the basilar membrane degenerate. The spiral ganglion, stria vascularis, and the cochlear branch of CN VIII may also atrophy. These progressive changes create a sensorineural hearing loss, particularly for higher frequency sounds.

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➤ Chapter Summary The ear can be separated into three main divisions: the outer, middle, and inner ear. The outer ear consists of the auricle and external auditory meatus and is responsible for localizing, collecting, and guiding sound into the middle ear. The tympanic membrane is the thin, concave, semitransparent, and opaque membrane that defines the boundary between the outer and middle ear. The ossicles, the three tiny bones of the middle ear, reside in the middle ear. Together, the malleus, incus, and stapes comprise the ossicular chain. The first ossicle, the malleus, is the largest and is attached to the tympanic membrane. The incus connects to the malleus. The head of the stapes is attached to the incus, while its footplate resides in the oval window, connecting it to the inner ear. Ligaments and tendons hold and balance the ossicular chain within the middle ear. The stapedius and tensor tympani muscles are the two main muscles of the ossicular chain; their contraction together stiffens the ossicular chain, known as the acoustic reflex. The medial wall of the middle ear space is home to the oval window, round window, promontory, and prominence of the lateral semicircular canal. The anterior wall contains the opening of the eustachian tube. The middle ear cavity is also defined by an anterior wall, superior wall, posterior wall, and floor. The inner ear contains structures related to hearing and balance. Structures related to hearing are located in both the osseous (bony) labyrinth and the membranous labyrinth. The vestibule is the entrance to the cochlea, and it is the shared cavity for all of the structures of the inner ear. The cochlea is the medial portion of the osseous labyrinth; it coils around a central core, known as the modiolus, in the shape of a snail’s shell. Two bony plates extend outward from the modiolus to form the osseous spiral lamina, which splits the cochlea into two passageways: the scala vestibuli (upper passageway) and scala tympani (lower passageway), both filled with perilymph. The scala media is part of the membranous labyrinth of the inner ear and is located between the scala vestibuli and scala tympani. The scala media is filled with endolymph. The floor of the scala media is the basilar membrane. The organ of Corti, the essential organ of hearing, rests on the basilar membrane. Within the organ of Corti are sensory cells, known as the inner and outer hair cells, and several kinds of supporting cells. The tectorial membrane rests on top of the hair cells. The vestibular system of the inner ear sends the brain sensory information regarding balance and equilibrium. The three osseous semicircular canals — anterior, posterior, and lateral — are arranged based on their anatomical orientation. Each canal joins the vestibule at the ampulla; within each ampulla is a sensory organ, known as the crista ampullaris. There are hair cells within the crista ampullaris, and a gelatinous cap, the cupola, lies on top of the hair cells. The utricle and saccule are part of the membranous labyrinth; the sensory organ for each of these structures is known as the macula. Membranous semicircular canals and membranous ampullae reside within their osseous counterparts. The eighth cranial nerve (CN VIII), known as the auditory, acoustic, vestibulocochlear, or auditory vestibular nerve is a sensory nerve. Its cochlear branch sends information regarding sound to the brain. The vestibular branch sends information related to equilibrium, movement, and balance to the brain. As individuals age, the structures of the outer, middle, and inner ear change. Presbycusis is the term for the acquired hearing disorder that results from the changes that accompany normal aging. While minor changes can impact the outer and middle ear, most of the changes with age that cause hearing loss occur in the inner ear, creating a sensorineural hearing loss for higher frequency sounds.

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➤ References Alvord, L. S., & Farmer, B. L. (1997). Anatomy and orientation of the human external ear. Journal of the American Academy of Audiology, 8(6), 383–390. Angelaki, D. E., & Cullen, K. E. (2008). Vestibular system: The many facets of a multimodal sense. Annual Review of Neuroscience, 31, 125–150. https://doi.org/10.1146/annurev.neuro.31​.060​ 407.125555 Aristeguieta, R., Miguel, L., Luis, B., & Germán, O. (2009). Tensor veli palatini and tensor tympani muscles: Anatomical, functional and symptomatic links. Acta Otorrinolaringológica Española, 61, 26–33. https://doi.org/10.1016/j.otorri​.2009​ .08.006 Atkinson, P. J., Huarcaya-Najarro, E., Sayyid, Z. N., & Cheng, A. G. (2015). Sensory hair cell development and regeneration: Similarities and differences. Development, 142, 1561–1571. https://doi​ .org/10.1242/dev.114926 Brownell, W. E. (1997). How the ear works: Nature’s solutions for listening. Volta Review, 99(5), 9–28. Burford, C. M., & Mason, M. J. (2016). Early development of the malleus and incus in humans. Journal of Anatomy, 229, 857–870. https://doi​ .org/10.1111%2Fjoa.12520 Dhanasingh, A. (2019). Cochlear duct length along the outer wall vs organ of Corti: Which one is relevant for the electrode array length selection and frequency mapping using Greenwood function? World Journal of Otorhinolaryngology–Head and Neck Surgery, 5(2), 117–121. https://doi.org/​ 10.1016%2Fj.wjorl.2018.09.004 Faddis, B. T. (2007). Structural and functional anatomy of the outer and middle ear. In W. Clark & K. Ohlemiller (Eds.), Anatomy and physiology of hearing for audiologists (pp. 93–108). Singular Publishing. Fettiplace, R., & Kim, K. X. (2014). The physiology of mechanoelectrical transduction channels in hearing. Physiological Reviews, 94(3), 951–986. https://doi.org/10.1152/physrev.00038.2013 Gagov, H., Chichova, M., & Mladenov, M. (2018). Endolymph composition: Paradigm or inevitability? Physiological Research, 67, 175–179. https:// doi.org/10.33549/physiolres.933684 Gelfand, S. A. (2016). Essentials of audiology (4th ed.). Thieme.

Hoogbergen, M. M., Schuurman, A. H., Rijnders, W., & Kon, M. (1996). Auricular hypermobility due to agenesis of the extrinsic muscles. Plastic Reconstruction Surgery, 98(5), 869–871. https:// doi.org/10.1097/00006534-199610000-00021 Hou, K. Y., & Wang, Z. C. (2013). Measurements of the vestibule of normal inner ear on volume CT. Chinese Journal of Radiology, 47, 500–504. https://doi.org/10.3760/cma.j.issn.1005-1201​ .2013.06.004 Kamrava, B., & Roehm, P. C. (2017). Systematic review of ossicular chain anatomy: Strategic planning for development of novel middle ear prosthesis. Otolaryngology–Head and Neck Surgery, 157(2), 190–200. https://doi.org/10.1177/01945​ 99817701717 Kaushal, N., & Kaushal, K. (2011). Human earprints: A review. Journal of Biometrics and Biostatistics, 2(5), 1–5. http://doi.org/10.4172/2155-6180.1000129 Langenheim, J. (2010). The last of the sea nomads. The Guardian. https://www.theguardian.com/ environment/2010/sep/18/last-sea-nomads Liugan, M., Zhang, M., & Cakmak, Y. O. (2018). Neuroprosthetics for auricular muscles: Neural networks and clinical aspects. Frontiers in Neurology, 8(752), 1–8. https://doi.org/10.3389/fneur​ .2017.00752 Lopez, I., Ishiyama, G., Tang, Y., Tokita, J., Baloh, R. W., & Ishiyama, A. (2005). Regional estimates of hair cells and supporting cells in the human crista ampullaris. Journal of Neuroscience Research, 82, 421–431. https://doi.org/10.1002/jnr.20652 Luers, J. C., & Hüttenbrink, K. (2015). Surgical anatomy and pathology of the middle ear. Journal of Anatomy, 228(2), 338–353. https://doi.org/​ 10.1111%2Fjoa.12389 Mark, C. (1982). Use of auricular cartilage in orbital floor reconstruction. Plastic and Reconstructive Surgery, 69(6), 951–955. http://doi.org/10​.1097/​ 00006534-198206000-00006 Menezes, P. L., Cabral, A., Morais, L. S., Rocha, L. P., & Passos, V. (2004). Resonance: A study of the outer ear. Pro Fono, 16(3), 333–340. Mukerji, S., Windsor, A. M., & Lee, D. J. (2010). Auditory brainstem circuits that mediate the middle ear muscle reflex. Trends in Amplification, 14(3), 170–191. https://doi.org/10.1177%2F108​ 4713810381771

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Naumann, A. (2007). Otoplasty: Techniques, characteristics and risks. German Medical Science Current Topics in Otorhinolaryngology, Head and Neck Surgery, 6, Doc04. Niemitz, C., Nibbrig, M., & Zacher, V. (2007). Human ears grow throughout the entire lifetime according to complicated and sexually dimorphic patterns — Conclusions from a cross-sectional analysis. Anthropologischer Anzeiger, 65(4), 391–413. http://doi.org/10.1127/anthranz/65/2007/391 Noussios, G., Chouridis, P., Kostretzis, L., & Natsis, K. (2016). Morphological and morphometrical study of the human ossicular chain: A review of the literature and a meta-analysis of experience over 50 years. Journal of Clinical Medicine Research, 8, 76–83. https://doi.org/10.14740%2Fjocmr2​369w Prasad, K. C., Mohiyuddin, S. M., Anjali, P. K., Harshita, T. R., Indu, V. G., & Brindha, H. S. (2019). Microsurgical anatomy of stapedius muscle: Anatomy revisited, redefined with potential impact in surgeries. Indian Journal of Otolaryngology–Head Neck Surgery, 71(1), 14–18. https://doi​ .org/10.1007/s12070-018-1510-5 Raphael, Y., & Altschuler, R. A. (2003). Structure and innervation of the cochlea. Brain Research Bulletin, 60(5–6), 397–422. https://doi.org/10.1016/ s0361-9230(03)00047-9 Rask-Andersen, H., Liu, W., Erixon, E., Kinnefors, A., Pfaller, K., Schrott-Fischer, A. & Glueckert, R. (2012). Human cochlea: Anatomical characteristics and their relevance for cochlear implantation. The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology, 295, 1791– 1811. https://doi.org/10.1002/ar.22599 Rodríguez-Vázquez, J. F. (2009). Development of the stapedius muscle and pyramidal eminence in humans. Journal of Anatomy, 215(3), 292–299. https://doi.org/10.1111%2Fj.1469-7580.2009​ .01105.x

Sadé, J. (1997). On the function of the pars flaccida: Retraction of the pars flaccida and buffering of negative middle ear pressure. Acta Otolaryngologica, 117(2), 289–292. https://doi.org/10.3109/00016​ 489709117789 Sanders, R. D., & Gillig, P. M. (2010). Cranial nerve VIII: Hearing and vestibular functions. Psychiatry (Edgmont), 7(3), 17–22. Sataloff, R. T., & Selber, J. (2003). Phylogeny and embryology of the facial nerve and related structures. Part II: Embryology. Ear Nose and Throat Journal, 82(10), 764–766; 769–772; 774. Spasic, M., Trang, A., Chung, L. K., Ung, N., Thill, K., Zarinkhou, G., . . . Yang, I. (2015). Clinical characteristics of posterior and lateral semicircular canal dehiscence. Journal of Neurological Surgery Part B: Skull Base, 76(6), 421–425. https://doi​ .org/10.1055%2Fs-0035-1551667 Swarts, J. D., Alper, C. M., Mandel, E. M., Villardo, R., & Doyle, W. J. (2011). Eustachian tube function in adults without middle ear disease. Annals of Otology, Rhinology, and Laryngology, 120(4), 220–225. https://doi.org/10.1177%2F0003489​ 41112000401 Szymanski, A., & Agarwal, A. (2018). Anatomy, head and neck, ear Eustachian tube. In StatPearls [Internet]. StatPearls Publishing. https://www.ncbi​ .nlm.nih.gov/books/NBK482338/ Todd, N. W., & Creighton, F. X. (2013). Malleus and incus: Correlates of size. Annals of Otology, Rhinology, and Laryngology, 122(1), 60–65. https://doi​ .org/10.1177/000348941312200111 Van Eyken, E., Van Camp, G., & Van Laer, L. (2007). The complexity of age-related hearing impairment: Contributing environmental and genetic factors. Audiology and Neurotology, 12(6), 345–358. https://doi.org/10.1159/000106478

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➤ Learning Outcomes Upon completion of this chapter, students will be able to: n

Understand the basics of sound and how we hear sound through wave frequencies.

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Learn about the physiology of the outer, middle, and inner ear.

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Understand the functions of the auditory central nervous system and its various structures.

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Learn about types of instrumentation available to examine the structures and functions of the ear.

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Review the three types of hearing loss — conductive, sensorineural, and mixed.

Although the structures of the ear are considered to be some of the smallest in the human body, they serve essential functions in the processes of hearing and balance. Each anatomical feature of the ear has a purpose in the conduction and transformation of air molecules through the outer, middle, and inner ear to the cerebral cortex of the brain. Before delving into the physiology of the ear, it is important to understand the basic properties of sound. This chapter covers the course of sound from the surrounding environment to the cortex, instrumentation in the field of audiology, and different types of hearing loss.

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➤ Properties of Sound To understand how hearing works, it is essential to know the basics of how sound waves travel to and within the ear. Sound can be defined as energy or the transfer that is propagated from one place to another in a wavelike motion. Sound is a pressure wave that is made up of high- and low-pressure areas that replicate as they move through a medium — such as air. Air particles in a state of rest are considered to be in equilibrium, unless these microscopic particles randomly collide with each other in what is known as Brownian motion. When air particles are disturbed, they do not actually move through space. Instead, the air particles are displaced, which results in a disturbance of the air particles in front of them, and a transfer of energy occurs from one particle to another. The particles then return to their original resting state, or equilibrium. The pattern that is formed from the displacement of air particles is known as vibratory motion (Figure 10–1). A cycle of vibratory motion is made of compressions and rarefactions (Figure 10–2): n

Compression occurs when the two air particles are pushed closer together to create higher areas of air pressure.

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Rarefaction occurs when the air particle is moving back to equilibrium, away from the other air particles, creating areas of low air pressure.

When an air particle is disturbed, it compresses forward to disturb the next air particle and transfer energy to it. Once the energy is transferred, the air particle returns to equilibrium. These vibrations create a wavelike motion that continues in a chain reaction, moving from one particle to the next. A simplified way to visualize the propagation of sound is to imagine a line of dominoes falling down. In this example, a single domino only makes a movement great enough to knock over the succeeding domino; however, energy is transferred from one domino to the next to knock the whole line down, creating a wave of dominoes. When put into motion, air particles tend to move from areas of higher pressure to areas

FIGURE 10–1.  Vibratory motion.

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of lower pressure. Once in motion, the air particles continue to move until energy is depleted. These characteristics of air particles are known as inertial properties. Frequency (Figure 10–3) is measured as the number of vibratory cycles that occur in a specified unit of time. It is most commonly referred to in cycles per second (cps) and is represented by hertz (Hz).

FIGURE 10–2. Rarefaction.

FIGURE 10–3.  Frequency and amplitude.

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If 200 cycles occurred per second, it would be equivalent to 200 Hz. The average human ear can detect sounds in the frequency range of 20 to 20,000 Hz (Rosen et al., 2011), with the most sensitivity (i.e., the ability to discern at the lowest intensity) between 2000 and 5000 Hz (Gelfand, 2016). The perceptual correlate of frequency is pitch. Higher frequency sounds (e.g., 3000 Hz) are higher in pitch than lower frequency sounds (e.g., 100 Hz). Amplitude can be described as the maximum displacement from equilibrium (Figure 10–3). The perceptual correlate of amplitude is loudness. The range of loudness that the average human can hear is expressed on a logarithmic scale of decibels of sound pressure level (dB SPL). Humans can hear sounds as quiet as 0 dB SPL and as loud as 140 dB SPL (Gelfand, 2016).

➤ Physiology of the Outer Ear Pinna and External Auditory Meatus The outer ear is a stationary structure that is responsible for gathering sound pressure waves and directing them into the ear. The grooves of the pinna help it act as a funnel to collect sound from all directions. The curved shape permits sound from behind the head to be reduced in intensity compared to those that are presented in the front of the head. The shape of the pinna aids in filtering background noise. As a result of these characteristics, the pinna assists in localizing the source of the sound. The ridges and grooves of the pinna also create cavities in the outer ear, which respond better to the frequency of sound that matches the cavity: n

When a certain structure vibrates in response to a specific frequency, it is known as resonant frequency. This resonant frequency occurs based on the size and shape of the grooves and ridges of an individual’s pinna. n While the pinna augments certain sounds like a microphone, it also dampens sounds due to its shape. This is called selective enhancement. n The concha has its own resonant characteristics, which results in amplification of sound in a variety of ranges. The pinna funnels sound pressure waves into the external auditory meatus (EAM). The size and structure of the EAM are important to its function in the transmission of sound energy from the outer ear to the middle ear. The EAM is essentially a tube; however, it is closed at one end by the tympanic membrane — separating it from the middle ear. This partition causes the EAM to have its own resonant frequency between 2000 and 4000 Hz (Gelfand, 2016). Sounds presented in this frequency range can be amplified by up to 20 dB (Gelfand, 2016). Cotton swabs can be dangerous when used to clean your ears. Medical specialists warn against it as it may lead to punctured eardrums or impacted wax. In a majority of cases, the ear canal does not need to be cleaned because there are several ways that earwax naturally gets loose and moves out of the ear canal. When you wash your hair while taking a shower, water enters the ear canal and results in loosening accumulated earwax; the skin in your ear canal grows outward in a spiral pattern, resulting in the earwax moving with it; earwax will also loosen and fall out by itself while you are asleep.

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The outer ear also has protective functions. The curved S shape of the EAM prevents foreign substances from traveling down the canal to rupture the tympanic membrane. Cerumen, or earwax, is created in the first one third of the EAM. The EAM also has small hairs, called cilia, lining its entrance. Both the cilia and cerumen prevent water from entering the ear canal and expel dirt and dead skin cells from the epithelial lining of the EAM. The acidic property of cerumen also prevents bacteria and fungi from growing in the EAM. Sometimes, outer ear anomalies may occur and cause both hearing impairments and cosmetic problems. Possible anomalies include the following conditions: Anotia:  absence of a pinna n Microtia:  partially developed “small” pinna n Preauricular tags:  congenital, benign skin tag formations posing cosmetic problems n Atresia:  absence of the EAM n A narrowing of the EAM (stenosis) is also possible. Atresia of the ear canal and microtia commonly present together. n Cauliflower ear:  an acquired disorder due to trauma to the outer ear. Wrestlers and boxers often have cauliflower ear because blows damage the structure of the pinna. n Squamous cell carcinoma:  malignant tumors that form on the pinna due to sun exposure n Osteoma:  bony tumors in the ear canal n External otitis:  inflammation of the ear canal due to bacteria and fungi

➤ Physiology of the Middle Ear Movement of the Tympanic Membrane and the Ossicular Chain Although the tympanic membrane is considered the boundary between the outer and middle ear, its physiology is discussed with that of the ossicular chain because of the interconnected relationship between these two structures. The tympanic membrane is located at the end of the EAM and vibrates in response to sound. If you recall, the tympanic membrane is concave, with its center pushed in at a 55° angle toward the ossicular chain of the middle ear (Todd, 2009): n

The tympanic membrane is attached to the ossicular chain via the malleus. n The incus is attached to the malleus and stapes. n The footplate of the stapes (which is the end of the ossicular chain) enters the oval window. The movement of the tympanic membrane corresponds to the compressions and rarefactions of the sound wave of the incoming signal. These movements travel down the ossicular chain to move the footplate of the stapes in the oval window. Together, the tympanic membrane and ossicular chain serve to transform acoustic energy and the sound pressure waves that vibrate the tympanic membrane into mechanical energy, which sets into motion the fluid of the inner ear. This process is known as the transformer action and increases the amplitude of the signal in three ways through n

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The transformer action helps to overcome the impedance (the blockage of energy flowing through the system) mismatch that exists because of the difference in the density between the air from the atmosphere and the fluid that fills the inner ear. If this impedance was not matched, less than 1% of the sound energy would pass to the fluid, and the rest would return back out of the ear. It is important, therefore, to examine each of the three ways that the tympanic membrane and ossicular chain contribute to the transformer action. The tympanic membrane vibrates in portions rather than as a single unit. The portions near the annular sulcus are stiffer and do not vibrate as well as those portions that are further away from the annular sulcus. Force, therefore, is allocated across multiple areas instead of one large unit and increases the pressure being distributed. A result of the vibration of the tympanic membrane is the area advantage. The surface area of the vibratory portions of the tympanic membrane is about 17 times bigger than that of the oval window (Kramer & Brown, 2018). Pressure equals force divided by area, so when the amount of area that force is exerted across is decreased, pressure increases. When sound energy is transmitted from the tympanic membrane to the significantly smaller oval window, the pressure on the oval window is increased by approximately 25 dB (Kramer & Brown, 2018).

In traumatic ossicular chain discontinuity — the middle-ear bones separate often due to chronic ear infections or a skull fracture of the temporal bone. Sometimes, facial paralysis accompanies the conductive hearing loss. If a penetrating skull injury results in a fractured, rotated, or dislocated malleus, incus, and stapes, as well as a perforated eardrum, a surgeon can replace the damaged structures and place an implant and reconstruct the eardrum with a titanium partial ossicular chain reconstruction prosthesis. The eardrum can be replaced with cartilage from the ear and fascia from the temporal muscle. Often, hearing may return to the normal range postoperatively.

When the tympanic membrane vibrates as a result of sound energy, it buckles slightly, or collapses (i.e., curved membrane buckling) so that the arm of the malleus does not move as much as the tympanic membrane. This reduces the speed at which the malleus is displaced and increases force — boosting the amplitude. The ossicular chain also functions as a lever : n

The manubrium acts as the long leg.

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The shorter segment of the lever is the long process of the incus.

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The incudomalleolar joint is the pivot point.

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The stapes is displaced in the oval window.

A lever is more efficient when the pivot point is closer to the unit being displaced. Because the incudomalleolar joint is close to the footplate of the stapes in the oval window, a small amount of pressure against the manubrium creates greater pressure at the oval window, adding about 2 dB of sound pressure to the signal (Welling & Ukstins, 2013). In addition to contributing to the transformer action and transmitting vibrations to the fluids of the inner ear, the ossicular chain serves to prevent the middle and inner ear from being negatively affected by the strong force of these vibrations. The ossicles are suspended by ligaments in the middle ear so that they are evenly balanced and do not excessively swing when stimulated with vibrations. When the vibrations 342

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When the tensor tympani muscle is contracted, the malleus moves medially and anteriorly at a right angle to the movement of the ossicular chain.

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When contracted without the stapedius muscle, the tensor tympani muscle functions to increase the tension of the tympanic membrane.

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Upon contraction, the stapedius muscle moves the stapes posteriorly at a right angle to the movement of the ossicular chain by applying force on the head of the stapes.

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The simultaneous contraction of the tensor tympani and stapedius muscles, therefore, exerts force in opposite directions and at right angles to the movement of the ossicular chain.

This acoustic reflex is triggered in response to high-intensity sounds by contracting the ossicular chain. This action lessens the admittance (the ease with which energy flows through the system) of the sound signal for lower frequencies and inhibits the stapes from vibrating excessively in the oval window. Even if the sound is presented to only one ear, the acoustic reflex will be triggered in both ears. This reflex occurs when a sound reaches an intensity of 80 to 90 dB above the threshold; however, the reflex response time is not quick enough to respond to sudden loud sounds, such as a gunshot or explosion (Deiters et al., 2019). The cranial nerves responsible for the acoustic reflex include the efferent fibers of the facial nerve (motor component) and the cochlear branch of the vestibulocochlear nerve (sensory component).

FIGURE 10–4.  Acoustic reflex. Source: Figure 12.4 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 507), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

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end, the ossicular vibration stops rather suddenly and simultaneously with the tympanic membrane, thus serving to diminish the distortion of sound in the middle ear. The muscles of the middle ear (i.e., tensor tympani and stapedius) also serve to protect the inner ear from excessive vibrations through involuntary dual muscle contractions called the acoustic reflex (stapedial reflex; stapedius reflex) (Jones et al., 2018) (Figure 10–4):

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

The tensor tympani and stapedius muscles are enclosed in the bony canals of the temporal bone and therefore contribute to the function of the middle ear. Only the tendons of these muscles enter the middle ear space. This organization of the middle ear space prevents excess muscular vibrations from interfering with the transmission of sound energy and decreases the overall mass of the ossicular chain. The tendons of these muscles also have unique elastic properties, which allow them to diminish the ossicular vibrations and contract the muscles less suddenly and more slowly. One more structure of the middle ear worth mentioning is the round window. The round window is located on the medial wall of the middle ear space and is the division between this space and the scala tympani of the cochlea. The flexible membrane of the round window protrudes toward the middle ear space. Thus, it contributes to the ability of the stapes to move inward in the oval window and compress the fluid inside the cochlea.

➤ Eustachian Tube The eustachian tube is named after the 16th-century Italian anatomist Bartolomeo Eustachi. Although the eustachian tube is not considered part of the middle ear, it contributes to the optimal functioning of the middle ear. At rest, the eustachian tube is collapsed and closed, but when opened (e.g., during swallowing or yawning), it serves to equalize the pressure of the middle ear with the atmospheric air pressure. Its sloped trajectory allows for secretions from the middle ear to drain into the nasopharynx. Contraction of the tensor veli palatini muscle is responsible for this opening of the eustachian tube to equalize pressure. Because atmospheric air pressure can vary greatly depending on elevation, the dilation of the eustachian tube allows humans to adapt and tolerate changes in air pressure. If the eustachian tube becomes swollen (e.g., during an upper respiratory infection), it does not drain adequately. Fluid can be trapped, and bacteria can grow, resulting in pus within the middle ear space. This is how a middle ear infection (i.e., otitis media) occurs. When an infection occurs, the structures of the middle ear stiffen, the eardrum is unable to adequately vibrate, and there is negative pressure in the middle ear cavity. These behaviors create a conductive hearing loss for lower frequency sounds. Following severe and chronic eustachian tube dysfunction, children commonly receive myringotomy tubes (Figure 10–5). A myringotomy surgical procedure allows for pressure equalization by making an incision in the ear canal instead of the eustachian tube; then a tympanostomy, during which a myringotomy tube is placed, can be performed. Relatedly, the adenoids, also known as pharyngeal tonsils, may potentially contribute to chronic infections in children. Frequent upper respiratory infections could result in swelling of the lymphoid tissue of the adenoids, which may potentially occlude the eustachian tube. Adenoid removal is a surgical option to reduce such complications (Skoloudik et al., 2018). Have you ever flown in a plane and experienced pain in your ears when the plane ascends and descends rapidly? This is because air pressure changes quickly, and there is a mismatch between the air pressure in the middle ear and the air pressure in the surrounding environment resulting in the tympanic membrane not vibrating normally. Since the eustachian tube is connected to the middle ear and regulates air pressure, it often does not have a fast enough reaction time to open and equalize pressure. Swallowing, yawning, or chewing gum opens the eustachian tube and allows the middle ear to get more air, thereby equalizing the air pressure.

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FIGURE 10–5.  Insertion of myringotomy tube within tympanic membrane.

It is possible for patients to experience a continually patulous, or “open,” eustachian tube, which can be severely unsettling with minimal options for symptom relief. The open eustachian tube may result in hearing an “echo” of our vocalizations, heartbeat, and breathing in the middle ear cavity. This sound awareness, termed autophonia, is often joined by awareness of vibrations within the middle ear cavity, specifically of the tympanic membrane. Possible etiologies include repeated overuse of decongestants and/or massive weight loss.

➤ Physiology of the Inner Ear The inner ear contains some of the smallest structures in the human body, but it plays a critical role in the process of hearing. In this section, the characteristics and function of key structures in the inner ear are detailed. Electrical events, the process of energy conversion, and the neural components of the auditory pathway are also reviewed. Finally, the inner ear is also home to the vestibular system, so its physiology is discussed.

Stimulation of the Cochlea The cochlea and cochlear branch of CN VIII are considered the sensorineural system of hearing because they are responsible for receiving (or “sensing”) the acoustic signal and changing it into neural impulses that are sent to and processed by the brain. The structures within the cochlea identify the frequency (spectral analysis), amplitude, and simple temporal characteristics of the incoming signal. This is considered the first step in the processing of auditory information. Before examining the physiology of the inner ear, it is important to summarize the path the signal has traveled so far: n

Sound waves are collected by the pinna and travel down the EAM to vibrate the tympanic membrane. The ossicular chain (beginning with the malleus) is attached to the tympanic membrane and thus also vibrates. 345

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n

Through the components of the transformer action, the acoustic energy that creates vibrations within the tympanic membrane and ossicular chain is transformed into mechanical energy.

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The footplate of the stapes resides in the oval window. Movement of the ossicles, therefore, stimulates the oval window to compress the perilymph of the scala vestibuli of the inner ear.

If you recall from Chapter 9, the scala vestibuli is the upper passageway of the cochlea, and it begins at the oval window. When the perilymph of the scala vestibuli is compressed by the stapes, Reissner membrane swells toward the scala media, and the basilar membrane rises toward the scala tympani (Figure 10–6). In other words, this compression travels all the way to the basilar membrane. To understand how the basilar membrane moves in response to stimulation, it is important to understand the work of Georg von Békésy (1956) and his traveling wave theory of hearing. In his experiments, Békésy constructed three-dimensional, enlarged, scaled models of the cochlea. The cochlea and osseous spiral lamina are wide at the base and narrow at the apex (Figure 10–6). Conversely, the basilar membrane (i.e., the cochlear partition because it separates the scala media from the scala tympani) is narrow at the base and wide at the apex. Because it is narrow, the base of the basilar membrane is tense and stiff, while the wide apex is flaccid. The base of the basilar membrane is about 100 times stiffer than the apex. Békésy found that as the stiffness of the basilar membrane increases, the frequency of its vibration increases. Because the basilar membrane gradually becomes wider toward the apex, it increases in mass. Mass and resonant frequency have a reciprocal relationship — as mass increases, resonant frequency deceases. The combination of these three characteristics of the basilar membrane (gradual increase in stiffness, mass, and width) allows the basilar membrane to analyze different frequencies.

FIGURE 10–6.  Structures involved in the transduction of sound within the inner ear. Source: Figure 12.8 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 510), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

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Hair cells (stereocilia) in the inner ear are important for hearing and balance because they bend in response to sound. Have you attended a rock concert where the band is playing music that is over 90 dB (equivalent to the sound of a lawn mower)? When sounds that are louder than 90 dB are heard by a person, these hair cells are temporarily damaged but will regain their shape in a couple of days. Just like grass, if you step on a patch of grass temporarily, the grass will bend but become upright as soon as you step off the patch. Now imagine listening to that 90-dB concert for an extended period without a break. This may result in permanent hearing loss as the hair cells will die, and like grass, if you step on the grass and do not get off for a long period, the grass will die as well. There are thousands of hair cells in each ear, and once human hair cells die, they cannot be restored. n

After the traveling wave reaches this point of maximum amplitude, it rapidly dampens so that there is only one peak.

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This peak occurs closer to the apex for low-frequency sounds and closer to the base for highfrequency sounds.

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When the wave travels along the basilar membrane, the OHCs shift in relation to the tectorial membrane, which is known as the shearing action. The shearing action is greatest at the site of maximum amplitude of the traveling wave on the basilar membrane.

In addition to the basilar membrane’s role in frequency selectivity, the inner and OHCs contribute to frequency analysis, but in different ways. The inner hair cells (IHCs) are responsible for frequency coding. Although the IHCs are not embedded within the tectorial membrane, they are still affected by the action of the basilar membrane. The U-shape of the stereocilia (i.e., cilia or sensory hairs) of the IHCs allows them to instead be stimulated by the movement of endolymph. The velocity of the flow of endolymph is greatest at the peak of the traveling wave of the basilar membrane; therefore, the IHCs are stimulated more at this point (Dallos et al., 1972). Despite this, the IHCs are not disturbed until the intensity of the signal is about 40 dB SPL or above (Dallos, 1992). The OHCs are different in shape and structure. In fact, they are able to change shape. The OHCs are motile, meaning that their length increases or decreases as a result of stimulation or inhibition (Evans & Dallos, 1993). The basilar membrane and the tectorial membrane are held in place by a hingelike apparatus on the side of the organ of Corti (Figure 10–6). This hingelike structure results in the tectorial membrane moving laterally over the hair cells, as the tectorial membrane and basilar membrane move up and down with the traveling wave. This lateral movement bends the top part of the cilia, pulls on

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Békésy determined that this structure of the basilar membrane causes a periodic pattern of fluid pressure (a wave) to propagate down the basilar membrane. The frequency of this wave matches that of the input signal. Békésy found that high-frequency sounds vibrate the basilar membrane at the basal end of the cochlea. Low-frequency sounds generate a longer traveling wave that moves toward the apex of the cochlea. Because different frequencies are processed in different regions (e.g., lower frequencies at the apex, higher frequencies at the base), the traveling wave splits up and organizes the frequencies of complex sounds. When a sound is composed of both high and low frequencies, the frequencies are divided and processed at the corresponding region of the basilar membrane. The peak amplitude of excursion of the traveling wave on the basilar membrane is the main point of neural excitation of the outer hair cells (OHCs) of the organ of Corti. The cilia of the OHCs of the organ of Corti are embedded within the tectorial (roof ) membrane (Figure 10–6).

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

the fine links, and opens the trap-door channels; therefore, the OHCs are stimulated more easily than the IHCs and at lower intensities. The OHCs, therefore, play a role in coding intensity for sounds with intensities lower than 40 dB SPL.

Transduction Up to this point, we have discussed how the mechanical properties of the basilar membrane and surrounding structures perform spectral analysis. The cochlea also functions as a transducer. The OHCs and IHCs are responsible for transduction — the process in which the mechanical vibrations of the basilar membrane are converted into electrochemical neural impulses (Eatock, 2010). Transduction is initiated by the frequency that maximally displaces the traveling wave on the basilar membrane (Figure 10–6). The hair cells are electrically stimulated based on their movement and the displacement of the basilar membrane. The stereocilia have a plasma core, and each hair cell gradually becomes thinner toward the bottom (Figure 10–7). The hair cells also are linked together by fibrin. Each hair cell has a single, stationary kinocilium — which is the tallest stereocilia. This structure of the hair cells enables

FIGURE 10–7.  Hair cell. The upward shift of the basilar membrane toward the scala vestibuli results in the cilia moving toward the kinocilium — depolarizing an individual hair cell that is bent by a pressure wave. This results in potassium channels opening to permit potassium to enter the hair cell with a resultant depolarization of the hair cell. When depolarization occurs, calcium channels at the base of the hair cell open and allow calcium to enter the hair cell, leading to the fusion of the synaptic vesicles with the cell membrane. Glutamate is then released across the synaptic cleft to the afferent neuron.

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The IHCs have a resting potential of about −40 mV, and the OHCs have a resting potential of about −70 mV (Dallos et al., 1982).

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The resting potential of the endolymph within the scala media is about +80 mV, known as the endocochlear potential (EP), due to its rich concentration of potassium and calcium ions (Figure 10–7). It is also worth noting that the ions of the endolymph within the scala media do not travel to or from the perilymph within the scala vestibuli and scala tympani. The scala media is also more positive compared to the scala tympani and scala vestibuli.

There are about 300 ion channels in the cells of the inner ear (Gabashvili et al., 2007). When the cilia are displaced toward the kinocilium, the ion channels open. Because the hair cells are linked together, the ion channels open very quickly. Ions flow from areas of high to low concentration, so when the ion channels open, the highly concentrated potassium ions enter the hair cell. The EP now has a negative charge, while the hair cell has a positive charge (about +40 mV). This process is known as depolarization because the membrane potential of the hair cell becomes less negative (i.e., more positive). Depolarization causes more ion channels to open laterally along the membrane of the hair cell. As a result, calcium enters the hair cell and potassium exits. The entry of calcium releases the neurotransmitter glutamate at the base of the hair cell, which excites the branch of the vestibulocochlear nerve (CN VIII) and generates the propagation of an action potential down its fibers. Momentarily, the movement of the calcium and potassium ions also causes hyperpolarization of the hair cell. The cell cannot be excited again until it reaches its resting potential. The sodium potassium pump uses adenosine triphosphate (ATP) to help to quickly restore the balance of ions within the hair cells. The balance of ions within the endolymph must also be restored for transduction to occur again. The function of the stria vascularis is to maintain appropriate ion concentration within the cochlea. Ion pumps pull the potassium across the stria vascularis, and through the process of osmosis, it travels back into the endolymph. This is how the endolymph sustains its potassium-rich composition and maintains its +80 mV EP, which is essential to transduction (Spicer & Schulte, 1996; Wangemann, 2006). The IHCs also convey information regarding the site of stimulation, and the OHCs amplify this signal. The depolarization of the OHCs creates a mechanical response that moves the basilar membrane. This is the physiological basis of otoacoustic emissions (Musiek & Baran, 2006). Following are different electrical potentials that occur during the process of transduction: n

Direct current (DC):  an electrical current that flows in one direction.

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Resting potentials:  are present when the cochlea is not being stimulated. It is a direct current potential. Both the hair cell and endolymph have resting potentials.

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Alternating current (AC):  is an electrical current that intermittently switches directions.

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Cochlear microphonics (CMs):  is a result of the stimulation of the hair cells of the cochlea. It is an AC potential that follows the movement of the acoustic signal as it stimulates the basilar 349

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them to pivot and therefore contributes to their stimulation. Put simply, when the basilar membrane is shifted upward toward the scala vestibuli, the cilia pivot toward the kinocilium, the cell is depolarized (its charge becomes more positive), and electrical activation occurs (Figure 10–7). The receptor potential created by this depolarization is dependent upon the intensity of the stimulus, so it gradually increases as the amplitude increases. Conversely, when the basilar membrane is shifted downward toward the scala tympani, the cilia pivot away from the kinocilium, the cell is hyperpolarized, and electrical activity is inhibited (i.e., the cell cannot fire). Keep in mind that the cochlea is only the size of a pea, so this movement is on an extremely miniscule scale. The process of transduction depends on several different electrical potentials:

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

membrane. CMs are made at the ciliated end of the hair cell. Both the CM potential and the summating potential (presented next) are receptor potentials because they are created only in reaction to a stimulus (Wever & Bray, 1930). n

Summating potential (SP):  is a change that occurs in the EP. It is a sustained, direct current that occurs when the organ of Corti is stimulated by sound. The IHCs become depolarized, so the potential within the cells is less negative. The difference in potential between the endolymph and the inner hair cell creates the SP. It is continued as long as the ear is stimulated with sound.

Another action potential is generated when the vestibulocochlear (i.e., auditory) nerve (CN VIII) is stimulated. The auditory nerve fibers fire in an all-or-none fashion, meaning that when they fire, they always fire to reach 100% amplitude (Welling & Ukstins, 2013). Action potentials are commonly called spikes because they occur quickly, typically in less than 2 ms. The lowest intensity of a sound that is required to increase the rate that the nerve fiber fires is known as the threshold for that frequency. If the intensity increases above this threshold, the amplitude of the action potential does not change. Since they always fire at 100%, what increases with the intensity of the stimulus is the rate at which the nerve fiber fires, known as the discharge rate or spike rate (spikes per second). The discharge rate gradually increases as the intensity increases. As a result, one nerve fiber can encode intensity through the rate of discharge over a limited range of intensities. Every nerve fiber has a characteristic (or best) frequency, which is the frequency that requires the minimum amount of intensity to cause the nerve fiber to fire. Some fibers have a high characteristic frequency, while others have a low one. This feature is dependent on the location of their corresponding hair cells. If you recall, high-frequency sounds vibrate the basilar membrane at the basal end of the cochlea, so nerve fibers that have high characteristic frequencies correspond with the hair cells at the base of the cochlea. Low-frequency sounds vibrate the basilar membrane at the apical end of the cochlea, so nerve fibers that have low characteristic frequencies correspond with the hair cells at the apex of the cochlea. As the nerve fibers of the cochlear branch of CN VIII depart the cochlea through the modiolus (Figure 10–8) on the way to the brainstem, they are organized according to frequency. The fibers with high characteristic frequencies reside around the outside of the cochlear branch, while those with low characteristic frequencies comprise the core of the branch. Thus, both CN VIII and the basilar membrane have tonotopic organization — meaning that each characteristic frequency corresponds to a location within the cochlear branch. The fibers of the vestibulocochlear nerve also encode temporal (time domain) information. If you were to graph the waveform of the stimulus sound and record the firing pattern of an individual nerve fiber, you would notice that when the nerve fiber fires, it does so at almost the same spot on the sine wave (smooth continuous waveform) of the stimulus. If you were to also measure the interval between successive spikes and count the number of times different intervals occurred, you would observe that the most repeated interspike interval is equivalent to the period of the waveform. All the other spikes happen at whole number multiples of the period of the waveform. Therefore, the individual nerve fibers of the cochlear branch of the vestibulocochlear nerve are able to encode the period of the stimulus waveform. Rather than measuring the individual action potential for a single nerve fiber, the whole-nerve action potential can also be measured, which is the sum of activity of multiple nerve fibers. Unlike the action potential of a single nerve fiber, the whole-nerve action potential is not measured in terms of its firing rate. The whole-nerve action potential can be measured by its amplitude or by its latency. As the intensity of the stimulus increases, so does the amplitude of the whole-nerve action potential. Latency is the time between the onset of the stimulus and the onset of the neural response. Latency can be graphed 350

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FIGURE 10–8.  A section through the center of the cochlea through the length of the modiolus.

as a function of stimulus intensity, known as a latency intensity function, which can be used to clinically assess the electrophysiology of the auditory mechanism: n

The latency of the response decreases as the intensity of the stimulus increases.

n

Amplitude increases with the intensity of the stimulus, which decreases the latency of the neural response.

➤ Auditory Central Nervous System The structures of the outer, middle, and inner ear are known as the peripheral auditory system. This section summarizes the neural path that the auditory signal follows beyond the cochlea and vestibulocochlear nerve (CN VIII), through what is known as the auditory central nervous system. An in-depth discussion of the structure and function of the nervous system is covered in Chapters 11 and 12. The following section details the path that the auditory stimulus has traveled so far through the peripheral auditory system: The acoustic signal was funneled into the pinna, was converted to mechanical energy by the middle ear, compressed the fluid of the cochlea to cause the movement of ions within the fluid and hair cells of the inner ear, stimulated the hair cells of the organ of Corti, which finally caused the nerve fibers of CN VIII to fire an action potential. The nerve fibers that fire these action potentials up the auditory central nervous system toward the cerebral cortex of the brain are part of the afferent pathway, which is the ascending pathway of the auditory CNS. Impulses can also be propagated in the opposite direction, from the cortex or brainstem toward peripheral structures. The nerve fibers that perform this function make up the efferent (or descending) pathway. There are more afferent than efferent pathways. For every 100 afferent nerve fibers, there are about two efferent nerve fibers (Bess & Humes, 2008). 351

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Afferent Pathway A schematic representation of the auditory pathway indicates that the first stop along the afferent pathway is the cochlear nucleus (Figure 10–9). One key characteristic of the auditory CNS that is present at the cochlear nucleus is redundancy. Each individual fiber of the cochlear branch of CN VIII splits into two branches prior to entry at the cochlear nucleus, and each branch supplies a different area of the cochlear nucleus. Therefore, a single piece of neural information from one ear is represented in several regions of the auditory cortex. The fibers of CN VIII terminate at the ipsilateral cochlear nucleus. Some processing of the signal occurs here, and the signal is coded into more complex information. Also, some of the cochlear nucleus nerve fibers have a range of intensity of up to 100 dB, and the firing rate increases as the intensity does (Wen et al., 2009). After the level of the cochlear nucleus, the nerve impulses have several options to follow for the rest of the course through the subcortical portion of the auditory CNS. All afferent nerve fibers finally synapse at a structure in the thalamus known as the medial geniculate body (Figure 10–9) and then ascend to the auditory cortex (Figure 10–9). Most ascending nerve fibers decussate (or cross over) along the pathway so that input from the two ears is compared for localization purposes. The first point of decussation is after the cochlear nucleus at the trapezoid body (Figure 10–9) at the level of the pons; some fibers decussate, while others do not. After they pass through the cochlear nucleus and potentially decussate via the trapezoid body, fibers may travel to the superior olivary complex (SOC, or superior olive) (Figure 10–9), which receives input from both ears (binaural integration) and plays a role in the localization of sound. The SOC also facilitates

FIGURE 10–9.  The central auditory pathway. Source: Figure 12.9 from Advance Review of SpeechLanguage Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 511), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

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the activity of the acoustic reflex of the middle ear muscles in conjunction with fibers of the facial nerve (CN VII). From the SOC on, information from both ears is conveyed on each side. Next up is the inferior colliculus (Figure 10–9), which is at the level of the dorsal midbrain (Figure 10–9). The inferior colliculus receives information from both ears from the SOC, and it also indirectly receives information from CN VIII through a tract known as the lateral lemniscus (Figure 10–9). The inferior colliculus also plays a role in the localization of sound, along with visual orientation through communication with the superior colliculus. Some nerve fibers may bypass the inferior colliculus, but they will terminate at the medial geniculate body with the rest of the afferent nerve fibers. The medial geniculate body maintains the tonotopic organization of the inner ear. From the medial geniculate body, nerve fibers project to the auditory cortex.

The efferent pathway, though an entirely different set of nerve fibers, travels almost the same route through the auditory CNS as the afferent pathway. The last stop along the efferent pathway is the SOC. Before entering the cochlea, at the SOC, the fibers either remain on the same side (known as uncrossed fibers) or decussate to enter the cochlea on the contralateral side (known as crossed fibers). The uncrossed fibers innervate the IHCs of the cochlea on the same side. At any point along the descending pathway of the auditory CNS, nerve fibers may also modify sensory information and can inhibit or stimulate impulses along the afferent pathway. The efferent pathway serves to shape and adjust the afferent sensory information. The acoustic reflex of the middle ear also regulates and modifies sensory information that ascends through the peripheral auditory system at the level of the SOC (Bess & Humes, 2008).

Auditory Cortex:  Auditory Processing and Speech Perception The temporal lobe of the brain is the site of auditory reception and processing. Auditory processing is the brain interpreting and using the sounds sensed by the ear, especially speech sounds, to make sense of the environment. There are two temporal lobes (one in each of the brain’s hemispheres). Heschl gyrus (Figure 10–10), also known as the transverse temporal gyrus, is found in the area of the primary auditory cortex that is located in the temporal lobe and receives the frequency characteristic of the signal. Tonotopic organization also continues to be maintained within the auditory cortex (Figure 10–10). Tonotopicity is complicated because cells that are receptive to different frequencies are found throughout each level of the central auditory system. The signal is processed subcortically as it travels through the peripheral auditory system and along the auditory central nervous system. These structures aid in the perception of pitch and loudness as well as the localization of sound. A structure within the temporal lobe known as the insula serves to process the temporal aspects of sound, and the auditory cortex also contributes to the localization of sound. In humans, the superior temporal sulcus and lateral belt areas within the temporal lobe are sensitive to the human voice. The understanding of the complex features of speech, however, known as speech perception, involves the activity of the auditory cortex. The auditory cortex uses the information gathered and refined at earlier sites along the auditory CNS to process and interpret the characteristics of speech. The most complex processing of auditory information occurs in areas of the primary auditory cortex as well as two other regions: the superior temporal gyrus and the temporo-parieto-occipital association area. The latter of these two regions houses Wernicke area, a structure crucial for receptive language skills (described further in Chapter 11). The temporal lobes also have connections with other areas within the cortex that contribute to the processing of the auditory signal. The frontal lobes aid in the storage of auditory memory. The

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FIGURE 10–10.  Tonotopic organization of Heschl gyrus. From Ascend Learning. Reproduced with permission from Anatomage.

parietal lobes are responsible for sensory integration: They incorporate sound with information regarding other senses, such as sight. The parietal lobes also are responsible for the association of sound with experiences. A subcortical area, the cerebellum, is involved in the timing of the processing of speech down to the millisecond.

➤ Vestibular System Though not essential for hearing, the vestibular system is part of the inner ear and is thus briefly discussed. If you recall from Chapter 9, there are three endolymph-filled semicircular canals (membranous canals enclosed in bony canals) that correspond to the orientation and movement of the body. These canals, the anterior, posterior, and lateral canals, are arranged perpendicularly to each other and communicate with each other via a dilation called the ampulla, which houses the crista ampullaris — the sensory organ of rotation. When the head moves, the endolymph within the semicircular canals pushes on the cap of the stereocilia (the cupola) and bends the stereocilia within the crista ampullaris. The direction of the movement of the stereocilia along with the orientation of the semicircular canals helps to map the direction of movement of the body. The sensory organs (maculae) (Figure 10–11) of the utricle and saccule are responsible for sensing the acceleration of the head (Deans, 2013): n

The macula within the utricle senses acceleration of forward/backward (horizontal) acceleration.

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The macula within the saccule senses vertical acceleration.

The macula, therefore, is responsible for the sensation of taking off on an airplane, and the utricle is responsible for the sensation one may feel if the airplane suddenly drops due to turbulence. The maculae 354

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FIGURE 10–11.  How the maculae respond to changes in the head position.

contain hair cells that are innervated with afferent fibers of the vestibular branch of CN VIII (Deans, 2013). When the hair cells are stimulated, they transform information from gravity and linear displacement into an electrical synapse with the nerve fibers of the vestibular branch of CN VIII. Adaptive functioning of the vestibular system originates in the cerebellum. The cerebellum interprets information from the inner ear and integrates information about body position, movement, and acceleration with other information from the proprioceptive system, such as joint and muscle movement and visual information, to create a sense of one’s body position in space.

➤ Instrumentation There are several tools that can be used to examine the structure and function of the ear. Some of the most common instrumentation methods are summarized in this section. Students should refer to their audiology coursework and textbooks for more information regarding diagnostic tools for hearing loss.

Otoscopy An otoscope (Figure 10–12) is a handheld light source commonly used to examine the tympanic membrane. Visible signs of a healthy tympanic membrane include superficial blood vessels and the reflection of the light from the otoscope as a result of the concave shape of the eardrum, known as the cone of light. Otitis media moves the tympanic membrane inward due to negative pressure in the middle ear space, so the cone of light will not be seen with the otoscope (Gelfand, 2016). Thus, the otoscope can be used as a diagnostic tool for otitis media. 355

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FIGURE 10–12. Otoscope.

Pure Tone Audiometry Pure tone audiometry measures air and bone conduction thresholds and can be used to diagnose conductive, sensorineural, or mixed hearing loss (Roeser, 2013). A single tone is presented in one ear, and the respondent indicates that they have heard the tone by raising the hand, pushing a button, or saying “yes.” Both ears are tested separately. The lowest level at which the sound is heard is the threshold. The frequencies usually tested with audiometry are those most critical for speech, language, and hearing — ranging from 250 to 8000 Hz. The threshold for each frequency in each ear is plotted on a graph known as an audiogram (Figure 10–13). On the audiogram, frequency is along the x-axis. The hearing levels (HL; in decibels) are listed from −10 to 120 dB down the y-axis. A threshold of 0 dB HL across all frequencies is considered perfect hearing. Normal hearing falls in the range of −10 to 15 dB HL (Clark, 1981): n The

air conduction threshold is a measurement of the lowest intensity in decibels at which a tone is perceived 50% of the time. The air conduction pathway is the one that sound waves follow when they enter the EAM and travel through the whole auditory system. Air conduction assessment uses earphones or small foam inserts. On the audiogram, unmasked air conduction scores are plotted using symbols: O indicates the right ear, and X indicates the left ear.

n The

bone conduction path is the one that occurs when sound waves vibrate the bones of the skull. Bone conduction bypasses the outer and middle ear, so it is a measure of sensorineural hearing loss. A bone vibrator, placed on the forehead or mastoid process, is used to measure bone conduction thresholds. Unmasked bone conduction scores are also plotted on the audiogram using symbols: [ indicates the right ear, while ] symbolizes the left ear. 356

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FIGURE 10–13.  An audiogram representing normal hearing in both ears. Source: Figure 12.21 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 532), by Celeste Roseberry-McKibbin, M. N. Hedge and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

Speech Reception Threshold Speech audiometry was originally developed at Bell Labs in the 1920s while researchers were studying the efficiency of communication systems. After World War II, many veterans who returned from the battlefield were suffering from noise-induced hearing loss. To attend to the needs of these veterans, the U.S. government established hearing rehabilitation services to evaluate and treat hearing loss. Audiologists used the initial work of Bell Labs to develop speech audiometry to test hearing and assess the auditory ability of these soldiers by using everyday words that were more representative than pure tones. The veterans were asked to repeat the words they heard. By measuring the ability to perceive speech, audiologists could determine the functional hearing ability of the soldiers to predict whether the use of hearing aids would be successful. When the audiologists viewed the results of speech audiometry testing on an audiogram, they could determine the speech reception threshold (SRT) that showed how well the soldiers could hear and understand ordinary conversation. The SRT is the softest level at which an individual can hear speech 50% of the time (Noordhoek et al., 1999). To find the SRT, the examinee wears a pair of headphones and repeats back the detected word. The audiologist records the softest decibel level the examinee can detect and repeat the target word. The SRT can also be measured in noise. Because individuals with hearing loss may have difficulty 357

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hearing when background noise is present, SRT measures how well someone can hear in different levels of background noise. Current research suggests that individuals with hearing loss learn to cope with this increased difficulty by attending to the single talker and not processing some of the information presented. Processing and listening effort is therefore reduced (Koelewijn et al., 2017).

Tympanometry Tympanometry assesses the movement of the eardrum (Onusko, 2004). To perform tympanometry, the audiologist places a small probe into each ear. These probes are connected to a device that pushes air into the examinee’s ear and records the movement of the eardrum on a graph called a tympanogram (Figure 10–14). The examinee does not need to answer or follow any instructions other than sitting still; thus, it is appropriate to use with both children and adults. Based on the shape of the tympanogram, an audiologist will be able to determine if the eardrum is too stiff, too flaccid, punctured, or if it is functioning correctly. Tympanometry is used to diagnose otitis media, a perforated eardrum, or ear canal that is impacted with wax or a foreign object.

Acoustic Reflex Testing The acoustic reflex can be assessed using a device called an immittance meter. Probes are inserted into the ears, and the immittance meter measures the acoustic reflex. Assessing the acoustic reflex can help an audiologist determine the intensity at which the acoustic reflex is triggered. If the intensity level at

FIGURE 10–14.  Tympanogram with pressure difference on the x-axis and compliance on the y-axis.

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which the acoustic reflex is triggered is higher than normal (about 85 dB SPL) (Gelfand, 1984), it may be indicative of facial (CN VII) or vestibulocochlear (CN VIII) nerve damage. Acoustic reflex testing has been used as a neonatal hearing screening to determine if further audiological evaluation is warranted. Premature infants with low birth weight are less likely to exhibit the acoustic reflex (Corteletti et al., 2018).

Otoacoustic Emissions

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transient-evoked OAEs (TEOAEs) that are elicited with very brief (transient) sounds, such as tone bursts or clicks

FIGURE 10–15.  Otoacoustic emissions. Source: Figure 12.20 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 531), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

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When the OHCs of the cochlea are stimulated, they vibrate, which makes an extremely quiet sound that echoes back into the middle ear space. The sounds that echo back can be measured and are known as otoacoustic emissions (OAEs) (Figure 10–15). There are several types of OAEs. They can be spontaneous or evoked. Two of the most common types of evoked OAEs are

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

n

distortion product OAEs (DPOAEs) that are elicited with two pure tone frequencies that are presented simultaneously and closely spaced at moderate intensity levels

Small foam inserts are placed in the ears to measure OAEs. The probes send sound into the ears and measure the OAEs that return. Individuals with normal hearing will produce OAEs. If OAEs are not produced, it is indicative of a hearing loss of at least 25 to 30 dB. Generally, OAE testing is used to examine the function of the cochlea; however, it can also indicate if there is a middle ear blockage because the sound sent by the probe will not be able to travel to the inner ear to be echoed back. It is important to note that spontaneous OAEs can occur even without an auditory stimulus and manifest in less than half of those with normal hearing (Serra et al., 2015). Like auditory brainstem response (ABR) procedures, the examinee does not need to follow any instructions other than sitting relatively still and quiet. Because of the simple procedure, measurement of OAEs is often used as a newborn hearing screening (Akinpelu et al., 2014). The examiner, however, must consider the high false-positive rate associated with this method of screening. Most recently, research has suggested that testing DPOAEs at higher frequencies can help reduce the false-positive in children (Olubumni et al., 2019). TEOAEs also provide objective data about the cochlea and normal functioning of the middle ear and refer to the OAE responses evoked by a click.

Auditory Brainstem Response Auditory brainstem response (ABR) is a diagnostic tool for sensorineural hearing loss (Skoe & Kraus, 2010). ABR testing uses surface electrodes to measure the electrical potential of the auditory pathway as it travels through the brainstem, specifically, from the cochlear nucleus to the inferior colliculus. These electrodes are connected to a computer, which records the brain waves that occur in response to sound heard during testing — known as auditory-evoked potentials. This testing does not require participant response while the computer records the participant’s brain activity. ABR testing is often used for newborn hearing screenings because it does not require an individual to follow instructions; the examinee can even sleep during the test. When it is used for a screening, ABR testing is less in-depth, as only one loudness level is tested on a pass/fail basis. If a baby fails the screening, referrals are made for more hearing tests.

Electrocochleography Electrocochleography (ECOG or ECochG) is another way to examine the function of the inner ear and auditory pathway (Pienkowski et al., 2018). ECOG can be performed with either invasive or noninvasive electrodes: n

Invasive electrodes, such as transtympanic (TT) needles, provide clearer, more precise electrical responses (with larger amplitudes) because the electrodes are very close to the voltage generators. The needle is positioned on the promontory wall of the middle ear and the round window. The patient is sedated with anesthesia and requires medical supervision.

n With

noninvasive, or extratympanic (ET) electrodes, the patient does not experience pain or discomfort, and there is no need for anesthesia, sedation, or medical supervision. When comparing the two methods, with noninvasive ECOG, the responses are smaller in magnitude.

More specifically, ECOG detects and records elevated pressure within the hair cells of the inner ear and auditory nerve fibers. ECOG measures four distinct features of “cochlear response,” including 360

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n OHCs n IHCs n

dendritic receptor potentials n spikes of auditory nerve fibers

➤ Types of Hearing Loss Before discussing the types of hearing loss, it is important to define some key vocabulary terms. Hearing loss can be caused by injury to any of the structures of the auditory mechanism, which impacts the ability of a structure to function: n

Hearing loss can occur in only one ear (unilateral) or in both ears (bilateral).

n

If an individual is born with hearing loss, it is called congenital, whereas it is acquired if it happens sometime after birth.

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If the hearing loss occurs before the acquisition of speech and language, it is known as prelingual hearing loss. Conversely, if the hearing loss occurs after the acquisition of speech and language, it is known as postlingual hearing loss. Because individuals with postlingual hearing loss have been exposed to speech and language patterns, depending on the amount of time spent with normal hearing, postlingual hearing loss tends to have less of an impact on communication than prelingual hearing loss (Kozak & Grundfast, 2009).

Hearing loss can develop gradually, or it can have a very sudden onset. It can be a more temporary or an acute condition, or it can be a more permanent, chronic condition. Hearing loss also can fluctuate in severity or it can gradually get worse over time. The range of severity of hearing loss (Clark, 1981) includes: n

normal:  from −10 to 15 dB HL n slight hearing loss:  from 16 to 25 dB HL n mild hearing loss:  from 26 to 40 dB HL n moderate hearing loss:  from 41 to 55 dB HL n moderately severe hearing loss:  from 56 to 70 dB HL n severe hearing loss:  from 71 to 90 dB HL n profound hearing loss:  91 dB HL or greater In general, hearing loss can be grouped into one of three categories: n conductive n sensorineural n

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ECOG is used in the identification of Ménière disease (a disorder of the inner ear that can lead to dizzy spells, vertigo, and hearing loss) as well as for intraoperative monitoring of the inner ear and auditory nerve (Ferraro, 2010). Audiologists require specialized training to perform ECOG. To perform the test, an electrode is placed either in the EAM or tympanic membrane, from the round window, or from inside the cochlea to measure the “cochlear response.” Invasive electrodes require sedation and anesthesia because a needle is inserted into the promontory wall.

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Conductive Hearing Loss Conductive hearing loss (Figure 10–16) occurs when sound is unable to be conducted through the outer and/or middle ear (Gelfand, 2016). Acoustic energy is not effectively transformed into mechanical energy, and this mechanical energy is not effectively transferred to the inner ear. Conductive hearing loss is the result of lesions of the outer and/or middle ear. Conductive hearing loss is not frequency specific. It occurs consistently regardless of stimulus frequency. Individuals with conductive hearing loss may have more trouble hearing soft sounds than loud sounds. Some common causes of conductive hearing loss include the following: n

Microtia — misshapen pinna

n

Atresia — when the EAM does not form appropriately during development. There are varying grades of severity to this condition: n

Grade 1:  Ear visibly looks normal; however, it is smaller than usual.

n

Grade 2:  Lower half of ear appears normal, but the ear canal may be slow or closed.

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Grade 3:  Small accumulation of skin and cartilage as well as lack of ear canal (aural atresia).

FIGURE 10–16.  Audiogram of a conductive hearing loss. Source: Figure 12.22 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 533), by Celeste RoseberryMcKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

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Grade 4: Absence of both the ear canal and external ear, often called anotia.

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Anotia — missing pinna

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Stenosis — ear canal is excessively narrow

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Otitis media — middle ear infection, which may be caused by eustachian tube dysfunction or the result of an upper respiratory infection. Middle ear infections commonly occur throughout childhood and are the most common reason that toddlers are prescribed antibiotics. Middle ear infections occur more frequently between 6 months and 1 year, 6 months. If undetected or reoccurring, otitis media can lead to delays in language acquisition (Casby, 2001). Research has shown that school-aged children who experience recurrent otitis media in early childhood entered elementary school at a disadvantage to those without recurrent otitis media (MacIntyre et al., 2010).

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Perforated tympanic membrane — hole in the eardrum that can be caused by chronic otitis media or trauma to the ear, such as a very loud noise

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Tympanosclerosis — scar tissue forms on the eardrum, usually as a result of recurrent otitis media. Usually has only a minor effect on hearing.

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Chronic middle ear disease — disrupts the incudostapedial joint and damages the ossicles, resulting in a moderate conductive hearing loss

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Impacted ear canal — the ear canal is excessively packed with earwax or a foreign substance

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Tumors in the ear canal or middle ear space — tumors can either be benign or malignant

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Otosclerosis — abnormal bone growth, usually around the footplate of the stapes, which impedes vibrations from effectively being transferred from the tympanic membrane to the oval window. Patients with otosclerosis frequently present with reduced bone conduction sensitivity at 2000 Hz (Margolis et al., 2016). This pattern of thresholds is termed Carhart notch and is often a diagnostic indicator.

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Bell palsy — may weaken the ossicles due to temporary paralysis of the stapedius muscle, resulting in a perception of increased loudness of low-frequency sounds

Sensorineural Hearing Loss A sensorineural hearing loss (SNHL) (Figure 10–17) is the product of damage to the inner ear or the pathways of CN VIII leading to the brain. SNHL may be frequency specific, depending on the etiology. Individuals may have difficulty hearing both soft and louder sounds. Sensorineural hearing loss cannot be reversed; damage is permanent. Some common causes of SNHL include the following: n

Congenital abnormalities, such as inherited genes, and/or genetic syndromes that negatively affect the development of the inner ear

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Presbycusis — hearing loss due to normal age-related changes in the inner ear

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Ototoxic drugs — medications that have harmful effects on the inner ear (e.g., gentamicin, streptomycin, tobramycin)

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Illness — such as rubella (German measles — first described as a separate disease by German physicians in 1814), syphilis (a bacterial infection usually spread by sexual contact), herpes (an infection caused by the herpes simplex virus), and meningitis (an inflammation of the

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n

n

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 10–17.  Audiogram of a sensorineural hearing loss. Source: Figure 12.23 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 533), by Celeste RoseberryMcKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

meninges), which can be transmitted from an infected mother to the baby through the placenta or during birth. These viruses and infections can also be transmitted from individual to individual through infected secretions. n

Acoustic trauma — also known as noise-induced hearing loss (NIHL) can be the result of a one-time exposure to intense sound (such as a blast or gunshot) or constant exposure to moderately loud sounds over time (such as an industrial job or a career as a rock musician). The hair cells become bent and broken by the high intensity of the acoustic signal. A common symptom of NIHL is tinnitus — which is a ringing or buzzing sound that may be incessant or can just be present immediately following exposure to a loud sound (Møller, 2011).

Mixed Hearing Loss Mixed hearing loss (Figure 10–18) is the result of coexisting conductive and sensorineural hearing loss. For example, if an individual had otitis media as well as SNHL due to ototoxic medications, the hearing loss would be classified as mixed.

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Physiology of Hearing and Balance

10

FIGURE 10–18.  Audiogram of a mixed hearing loss. Source: Figure 12.24 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 534), by Celeste RoseberryMcKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

➤ Chapter Summary Sound is defined as energy or transfer that is propagated from one place to another in a wave motion. Air is one of the mediums that sound travels through. The outer ear is an immovable structure, and its main function is to gather sound pressure waves and direct them into the ear. The ridges and grooves of the pinna also create cavities in the outer ear, which respond better to the resonant frequency of the cavity. The pinna funnels sound pressure waves into the EAM. The size and structure of the EAM are critical to its function in the transmission of sound energy from the outer ear to the middle ear. The outer ear also performs protective functions. The tympanic membrane is located at the end of the EAM and vibrates in response to sound. Together, the tympanic membrane and ossicular chain serve to transform acoustic energy, or the sound pressure waves that vibrate the tympanic membrane, into mechanical energy, which sets the fluid of the inner ear into motion. This process is known as the transformer action, and it increases

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the amplitude of the signal in three ways: through the area advantage, curved membrane buckling, and lever action. The muscles of the middle ear, specifically the tensor tympani and stapedius, also serve to protect the inner ear from excessive vibrations through dual muscle contractions termed the acoustic reflex. The footplate of the stapes resides in the oval window. Thus, movement of the ossicles stimulates the oval window to compress the perilymph of the scala vestibuli of the inner ear, creating compressions that travel all the way to the basilar membrane. The cochlea and cochlear branch of CN VIII are considered the sensorineural system of hearing because they are responsible for receiving (or “sensing”) the acoustic signal and changing it into neural impulses that are sent to and processed by the brain. The mass, stiffness, and width of the basilar membrane allow it to analyze different frequencies, and a traveling wave is propagated down the membrane. The traveling wave splits up and organizes the frequencies of complex sounds. The cochlea also functions as a transducer. The OHCs and IHCs are responsible for transduction, the process in which the mechanical vibrations of the basilar membrane are converted into electrochemical neural impulses, which are sent to the auditory CNS. The process of transduction depends on several different electrical potentials. The action potential is generated when CN VIII is stimulated. Every nerve fiber has a characteristic frequency, which is the frequency that requires the minimum amount of intensity to cause the nerve fibers to fire. CN VIII and the basilar membrane have tonotopic organization, meaning that each characteristic frequency corresponds to a location within the cochlear branch. There are several afferent pathways that an impulse can travel through the auditory CNS. Most ascending nerve fibers decussate along the pathway so that input from the right ear crosses over to the left side, and vice versa. The auditory CNS has characteristics of redundancy and binaural integration. The efferent pathway follows almost the same route as the afferent pathway. The temporal lobe is the side of auditory reception and processing. There are several areas within the temporal lobe, specifically the primary auditory cortex, that process speech sounds. The vestibular system is part of the inner ear and processes information about body position and acceleration in space. There are several tools that can be used to examine the function of the ear including (but not limited to) otoscopy, pure tone audiometry, tympanometry, acoustic reflex testing, ABR, otoacoustic emissions, electrocochleography, and speech reception threshold. Hearing loss is caused by damage to the outer, middle, and/or inner ear or CN VIII. There is a severity range of hearing loss, ranging from normal hearing to profound hearing loss. Hearing loss can be grouped into the following categories: conductive, sensorineural, and mixed. It is important for students studying communication sciences and disorders to understand how structures of the ear work together to effectively diagnose and treat hearing loss.

➤ References Akinpelu, O. V., Peleva, E., Funnell, W. R., & Daniel, S. J. (2014). Otoacoustic emissions in newborn hearing screening: A systematic review of the effects of different protocols on test outcomes. International Journal of Pediatric Otorhinolaryn-

gology, 78(5), 711–717. https://doi.org/10.1016/j​ .ijporl.2014.01.021 Bess, F. H., & Humes, L. E. (2008). Audiology: The fundamentals (4th ed.). Lippincott Williams & Wilkins, Wolters Kluwer Health.

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Casby, M. W. (2001). Otitis media and language development: A meta-analysis. American Journal of Speech-Language Pathology, 10(1), 65–80. https://doi.org/10.1542/peds.113.3.e238 Clark, J. G. (1981). Uses and abuses of hearing loss classification. ASHA, 23(7), 493–500. Corteletti, L., Araújo, E., Duarte, J., Zucki, F., & Alvarenga, K. (2018). Acoustic reflex testing in neonatal hearing screening and subsequent audiological evaluation. Journal of Speech Language and Hearing Research, 61(7), 1784–1793. https://doi​ .org/10.1044/2018_jslhr-h-16-0291 Dallos, P. (1992). The active cochlea. Journal of Neuroscience, 12(12), 4575–4585. https://doi.org/​10​ .1523/jneurosci.12-12-04575.1992 Dallos, P., Billone, M. C., Durrant, J. D., Wang, C. Y., & Raynor, S. (1972). Cochlear inner and outer hair cells: Functional differences. Science, New Series, 117(4046), 356–358. https://doi.org/​ 10.1126/science.177.4046.356 Dallos, P., Santos-Sacchi, J., & Flock, A. (1982). Intracellular recording from cochlear outer hair cells. Science, 218, 582–584. https://doi.org/​10​ .1126/science.7123260 Deans, M. R. (2013). A balance of form and function: Planar polarity and development of the vestibular maculae. Seminars in Cell and Developmental Biology, 24(5), 490–498. https://doi.org/​ 10.1016/j.semcdb.2013.03.001 Deiters, K. K., Flamme, G. A., Tasko, S. M., Murphy, W. J., Greene, N. T., Jones, H. G., & Ahroon, W. A. (2019). Generalizability of clinically measured acoustic reflexes to brief sounds. Journal of the Acoustical Society of America, 146, 3993. https:// doi.org/10.1121%2F1.5132705 Eatock, R. (2010). Auditory receptors and transduction. In E. Goldstein (Ed.), Encyclopedia of perception (pp. 184–187). SAGE Publications. Evans, B. N., & Dallos, P. (1993). Stereocilia displacement induced somatic motility of cochlear outer hair cells. Proceedings of the National Academy of Sciences of the United States of America, 90(18), 8347–8351. https://doi.org/10.1073​%2F​ pnas.90.18.8347 Ferraro, J. A. (2010). Electrocochleography  —  A review of recording approaches, clinical applications and new findings in adults and children. Journal of the American Academy of Audiology, 21, 145–152. https://doi.org/10.3766/jaaa.21.3.2 Gabashvili, I. S., Sokolowski, B. H., Morton, C. C., & Giersch, A. B. (2007). Ion channel gene expres-

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sion in the inner ear. Journal of the Association for Research in Otolaryngology, 8(3), 305–328. https:// doi.org/10.1007/s10162-007-0082-y Gelfand, S. A. (1984). The contralateral acoustic reflex threshold. In S. Silman (Ed.), The acoustic reflex: Basic principles and clinical applications (pp. 137–186). Academic Press. Gelfand, S. A. (2016). Essentials of audiology (4th ed.). Thieme. Jones, H. G., Greene, N. T., & Ahroon, W. A. (2018). Human middle-ear muscles contract in anticipation of acoustic impulses: Implications for hearing risk assessments. Hearing Research, 378, 53–62. https://doi.org/10.1016/j.heares.2018.11.006 Koelewijn, T., Niek, J., Versfeld, S., & Kramer. E. (2017). Effects of attention on the speech reception threshold and pupil response of people with impaired and normal hearing. Hearing Research, 354, 56–63. https://doi.org/10.1016/j.heares​ .2017.08.006 Kozak, A. T., & Grundfast, K. M. (2009). Hearing loss. Otolaryngologic Clinics of North America, 42(1), 79–85. https://doi.org/10.1016/j.otc.2008​ .09.008 Kramer, S., & Brown, D. K. (2018). Audiology: Science to practice (3rd ed.). Plural Publishing. MacIntyre, E. A., Karr, C. J., Koehoorn, M., Demers, P., Tamburic, L., Lencar, C., & Brauer, M. (2010). Otitis media incidence and risk factors in a population-based birth cohort. Pediatrics and Child Health, 15(7), 437–442. https://doi​ .org/10.1093%2Fpch%2F15.7.437 Margolis, R. H., Wilson, R. H., Popelka, G. R., Eikelboom, R. H., Swanepoel, D., & Saly, G. L. (2016). Distribution characteristics of air-bone gaps: Evidence of bias in manual audiometry. Ear and Hearing, 37(2), 177–188. https://doi.org/10​ .1097%2FAUD.0000000000000246 Møller, A. R. (2011). Epidemiology of tinnitus in adults. In A. R. Møller, B. Langguth, D. DeRidder, & T. Kleinjung (Eds.), Textbook of tinnitus (pp. 29–37). Springer. Musiek, F. E., & Baran, J. A. (2006). The auditory system: Anatomy, physiology, and clinical correlates. Allyn & Bacon. Noordhoek, I. M., Houtgast, T., & Festen. J. M. (1999). Measuring the threshold for speech reception by adaptive variation of the signal bandwidth. II. Normal-hearing listeners. Journal of the Acoustical Society of America, 105(5), 2895–2902. https:// doi.org/10.1121/1.428452

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Olubumni, V., Akinpeula, W., Robert, J., Funnell, S., & Daniel, J. (2019). High-frequency oto­acoustic emissions in universal newborn hearing screening. International Journal of Pediatric Otorhinolaryngology, 127, 1–6. https://doi.org/10.1016/j.ijporl​ .2019.109659 Onusko, E. (2004). Tympanometry. American Family Physician, 70(9), 1713–1720. Pienkowski, M., Adunka, O. F., & Lichtenhan, J. T. (2018). Editorial: New advances in electrocochleography for clinical and basic investigation. Frontiers in Neuroscience, 12(310), 1–5. https:// doi​.org/10.3389/fnins.2018.00310 Roeser, R. J. (2013). Roeser’s audiology desk reference (2nd ed.). Thieme. Rosen, S. & Howell, P. (2011). Signals and systems for speech and hearing (2nd ed.). BRILL. Serra, L., Novanta, G., Sampaio, A. L., Augusto Oliveira, C., Granjeiro, R., & Braga, S. C. (2015). The study of otoacoustic emissions and the suppression of otoacoustic emissions in subjects with tinnitus and normal hearing: An insight to tinnitus etiology. International Archives of Otorhinolaryngology, 19(2), 171–175. https://doi.org/​10.10​ 55%2Fs-0034-1374648 Skoe, E., & Kraus, N. (2010). Auditory brain stem response to complex sounds: A tutorial. Ear and Hearing, 31(3), 302–324. https://doi.org/10.109 7%2FAUD.0b013e3181cdb272 Skoloudik, L., Kalfert, D., Valenta, T., & Chrobok, V. (2018). Relation between adenoid size and otitis media with effusion. European Annals of Otorhino-

laryngology, Head and Neck Diseases, 135(6), 399– 402. https://doi.org/10.1016/j.anorl.2017​.11.011 Spicer, S. S., & Schulte, B. A. (1996). The fine structure of spiral ligament cells relates to ion return to the stria and varies with place-frequency. Hearing Research, 100, 80–100. https://doi.org/​ 10.1016/0378-5955(96)00106-2 Todd, W. (2009). Tympanum-canal angles anteriorly, anteroinferiorly, and inferiorly: A postmortem study of 41 adult crania. Ear, Nose and Throat Journal, 88(9), E22–E27. von Békésy, G. (1956). Current status of theories of hearing. Science, New Series, 123(3201), 779–783. https://doi.org/10.1126/science.123.3201.779 Wangemann, P. (2006). Supporting sensory transduction: Cochlear fluid homeostasis and the endocochlear potential. Journal of Neurophysiology, 576(1), 11–21. https://doi.org/10.1113%2Fj physiol.2006.112888 Welling, D. R., & Ukstins, C. A. (2013). Fundamentals of audiology for the speech-language pathologist. Jones & Bartlett Learning. Wen, B., Wang, G. I., Dean, I., & Delgutte, B. (2009). Dynamic range adaptation to sound level statistics in the auditory nerve. Journal of Neuroscience, 29(44), 13797–13808. https://doi.org/10.15​ 23%2FJNEUROSCI.5610-08.2009 Wever, E. G., & Bray, C. W. (1930). Action currents in the auditory nerve in response to acoustical stimulation. Proceedings in the National Academy of Science, 16, 344–350. https://doi.org/10.1073​ %2Fpnas.16.5.344

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➤ Learning Outcomes Upon completion of this chapter, students will be able to: n

Describe the structure and function of a neuron.

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Describe types of neuroglia and their varying functions.

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Identify the major functions of the right and left cerebral hemispheres.

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Understand the basic function of the ventricular system.

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Understand and describe the major language-specific structures of the central nervous system and how these structures contribute to linguistic communication.

Before one can understand how the function of the brain is altered by disease or damage, the student of speech-language pathology first must comprehend basic information about normal brain anatomy and how a normal and healthy brain functions.

➤ Cells of the Nervous System The cells that make up the nervous system are divided into two basic categories depending on their functions. These are the two categories of neurons and neuroglia: n

Neurons are cells of the nervous system responsible for electrochemically transmitting and processing information. Neurons are the cells in which language, cognition, and motor 369

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movements such as speech and swallowing originate. Neurons transmit motor impulses from the brain to the muscles of the body, and they transmit sensory impulses from the sensory receptors in body (such as from the retina of the eyes and cochlea of the ears) to the brain. n

Neuroglia, also known simply as glial cells, are several types of nervous system cells that act to provide important structural and physiological support to neurons. However, neuroglia are not directly involved in information processing.

Neurons Neurons are specialized cells of the nervous system responsible for communicating via an electrochemical system of cellular communication. Neurons connect, or synapse, with other neurons. Neurons are capable of receiving electrochemical signals from other neurons or transmitting electrochemical signals to other neurons. There are three basic divisions of neurons — interneurons, motor neurons, and sensory interneurons: n

Interneurons are responsible for conjoining neurons to each other within the same area of the brain. They are responsible for the processing and interpreting of information rather than transmission of information.

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Motor neurons are responsible for transmitting impulses of motor movement from the brain and spinal cord out to the body where those impulses of motor movement are executed by the muscles of the body.

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Sensory neurons are responsible for transmitting sensory information from sensory receptor cells located in the body to the spinal cord or brain where those impulses are processed and interpreted.

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Sensory and motor neurons are concerned with the transmission of information from one part of the body to the other.

A neuron is made up of a cell body, also known as a soma, dendrites, and an axon (Figure 11–1): n

The cell body/soma is the portion of the neuron that contains the nucleus, the organelles, and the cytoplasm.

n

From the soma there are many projections, known as dendrites, that reach out and synapse with other neurons (Figure 11–1). Dendrites receive incoming electrochemical signals from other neurons and transmit these signals toward the soma.

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The single, long projection extending from the soma of the neuron is the axon (Figure 11–1). The axon is responsible for transmitting outgoing electrochemical signals from the soma to other neurons.

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Motor and sensory neurons have axons wrapped in a white substance made of proteins and fat that is known as myelin (Figure 11–1): n

n

n

Myelin, or the myelin sheath, functions as a form of electrical insulation for axons (like plastic coating on an electrical wire) and works to facilitate the effective and speedy transmission of signals between neurons along their axons. An axon coated in myelin can transmit an electrical signal at speeds of up to 328 feet per second, whereas an unmyelinated neuron transmits at speeds of about 3 feet per second. The myelinated axons of sensory neurons largely constitute the sensory pathways in the nervous system, and the myelinated axons of motor neurons largely constitute the motor 370

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pathways in the nervous system. Some of these axons that are responsible for transmitting sensory or motor signals through the body can be up to a meter in length before synapsing with the dendrites of another neuron. n

n

Because of the presence of myelin on these axons, motor and sensory neurons are said to consist of white matter because the myelin on their axons makes these neurons visually appear white. White matter is found throughout the nervous system. White matter is responsible for transmission of information for connecting different areas and structures of the brain to one another and enabling them to communicate.

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Interneurons are unmyelinated and are lacking the white fatty myelin sheath. The lack of myelin causes interneurons to have a gray appearance. Given this gray appearance, interneurons are referred to as being made of gray matter.

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Gray matter is also found throughout the nervous system. Gray matter lacks myelin and is more concerned with the processing and regulating of information than transmission of information as in the case of white matter.

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White matter and gray matter can be seen in a section of the brain with the naked eye. See Figure 11–2 where the myelinated sensory and sensory pathways in the brain (white matter) appear whiter than the surrounding unmyelinated areas (gray matter).

Before the axon of a neuron synapses with the dendrites of other neurons, it divides into axon terminals (Figure 11–1). At these axon terminals, the axon synapses with the dendrites of other neurons (Figure 11–1). At the terminal buttons, neurons communicate with each other via the cell-to-cell process known as synaptic transmission: 371

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FIGURE 11–1.  Neuron and neuroglia.

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 11–2.  Coronal section of the brain showing white matter and gray matter. Reproduced with permission from Anatomage.

n

Synaptic transmission is the exchange of electricity or the exchange of both chemicals and electricity between neurons. This exchange occurs at the synapse (Figure 11–1), which is the point of communication between neurons.

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What passes from one neuron to another, the electrochemical signal, is referred to as an action potential. The neuron that is transmitting an action potential toward the synapse is known as the presynaptic neuron (Figure 11–1). The neuron that is receiving the signal across the synapse is the postsynaptic neuron (Figure 11–1). Pre- and postsynaptic neurons do not actually physically contact one another. There is a space between the presynaptic axon and postsynaptic dendrite known as the synaptic cleft.

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Communication between neurons begins with generation of an action potential within a neuron. When a neuron generates an action potential, that action potential is transmitted away from the soma of the neuron, along the axon, until the action potential reaches the synapse. At the synaptic cleft, the presynaptic neuron releases chemicals known as neurotransmitters to activate chemical receptors on the postsynaptic neuron. This triggers the release of an action potential within the postsynaptic neuron that propagates the signal through the postsynaptic neuron to the next synapse in the chain. In this way, neurons transmit electrochemical signals throughout the body.

Neuroglia Neuroglia are also known as glial cells, and when first discovered and for a long time afterward, scientists did not know or understand most of their function. It was taken for granted that neuroglia existed

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simply for physical, structural support for the neurons. More recently, however, the differentiation and function of neuroglia and their importance to the function of neurons has become better understood. Some examples of these functions of neuroglial cells are that they aide in metabolic support of neurons (Lee et al., 2012), they regulate blood flow to neurons (Koehler et al., 2008), and some neuroglia aide in neuronal development (Barres, 2008). There are two neuroglial cells that are responsible for the production of myelin — Schwann cells and oligodendrocytes: Schwann cells (Figures 11–1 and 11–3) are responsible for producing the myelin sheath surrounding the axons of motor and sensory neurons within the peripheral nervous system: n

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The gaps on the axons formed between Schwann cells are the nodes of Ranvier (Figure 11–1).

While Schwann cells produce myelin in the peripheral nervous system, in the central nervous system, neuroglia known as oligodendrocytes produce the myelin sheath on axons of neuron (Figures 11–1 and 11–3): n

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Each Schwann cell provides a single segment of myelin sheath on a single axon and is located directly on the axon (Figures 11–1 and 11–3).

Unlike Schwann cells that each service a single segment of myelin on a single axon, oligodendrocytes have multiple processes that extend from the oligodendrocyte’s cell body out to the axons of multiple neurons (Figures 11–1 and 11–3) and supply the axons of these neurons with myelin. Each of these processes reaching out from the soma of the oligodendrocyte supplies one segment of myelin to one axon. In this way, myelinated axons in the central nervous system may receive myelin from multiple oligodendrocytes.

Another important neuroglial cell type is astrocytes. These cells appear star shaped due to their many projections (Figure 11–3); therefore, the Greek term astro is used to refer to them: Neuroanatomy and Neurophysiology:  Part 1

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FIGURE 11–3.  Glial cells.

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Astrocytes provide structural support for neurons in the intercellular space between neurons in the central nervous system. They also work to maintain homeostasis in the central nervous system and can release additional energy to neurons if needed. At the end of each of an astrocyte’s projection, they have end feet. The end feet of astrocytes reach toward synapses between neurons and assist in processing waste created at the synapse. These end feet also assist to seal off the circulatory system from the neurons. Astrocyte’s end feet create a layer that helps to establish the blood–brain barrier (Figure 11–4). The blood– brain barrier is a protective layer of cells that keep such unwanted or dangerous molecules such as poison or pathogens from moving into the brain from the circulatory system. The blood–brain barrier also, and simultaneously, allows nutrients from the circulatory system to pass into the brain from the circulatory system for nutritive purposes. Astrocytes are also important in that, in the case of lesion or injury within the central nervous system, they will multiply around the lesion and create a barrier around the injury. This protective process of astrocyte proliferation around an injury is known as astrogliosis. The barrier of proliferating astrocytes formed around an injury in the central nervous system is known as a glial scar. Glial scars are protective in nature and work to contain the spread of inflammatory cells from the injury.

Microglia are smaller immunological glial cells of the central nervous system that account for 10% to 15% of the brain: n

Microglia are the strongest line of immune defense of the central nervous system. Microglia seek out and consume cellular waste products, neuron tangles, and damaged neurons, and they respond instantaneously to invasive pathogens. In the case of damaged neurons, microglia will migrate into the area of damage and clear out damaged or unwanted tissue (Figure 11–5).

FIGURE 11–4.  Astrocyte with end feet creating blood–brain barrier

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FIGURE 11–5.  Microglia congregated into a group around a blood vessel (center of image). Source: CDC Public Health Image Library/Dr. Flynt.

➤ The Central Nervous System

n The

central nervous system (CNS) is composed of the brain and the spinal cord. The structures of the CNS are located at midline (centrally) in the body.

n The

peripheral nervous system (PNS) is composed of the sensory and motor nerve tracts that course between the CNS and the rest of the body. Whereas the structures of the CNS are located centrally in the body, the neural pathways that constitute the PNS are located less centrally and more laterally or peripherally in the body (Figure 11–6).

The Brain The brain is a 3-pound organ in our skull that consumes one fifth of the oxygen our bodies gather from the environment. The brain mediates all thought, language, intelligence, movement, and balance. It receives and processes all sensory information from our bodies. The brain is composed of three primary components: the cerebrum, the brainstem, and the cerebellum (Figure 11–7). The cerebrum is the most superior section of the brain and is a large, gray, and rounded portion of the brain with a wrinkled appearing surface (Figure 11–7). The cerebrum is the portion of the brain located above the brainstem that is composed of many smaller and important anatomical structures: n

The cerebrum is where our highest and most complex level of cognition (memory, attention, problem-solving, social inhibitions, etc.), language, and most skilled motor movement is generated. When you are conscious and aware of your surroundings, appreciate beauty, drive your car, complete homework, or complete a task as simple as brushing your teeth, you are very much employing your cerebrum. 375

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The nervous system is composed of two major divisions — the central nervous system and the peripheral nervous system (Figure 11–6):

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FIGURE 11–6.  Central nervous system and peripheral nervous system. Reproduced with permission from Anatomage.

FIGURE 11–7. Brain: cerebrum, cerebellum, and brainstem. Reproduced with permission from Anatomage.

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A condition known as anencephaly is a birth defect in which a baby fails to develop the cerebrum. Children born with this condition are incapable of ever having a conscious awareness of their surroundings and are stillborn or do not survive long after birth.

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The most superficial tissue of the cerebrum is a thin layer known as the cerebral cortex, seen as the surface of the cerebrum in Figure 11–7: n

The gray color of the cerebral cortex is due to it being composed of unmyelinated neurons (gray matter). 376

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n

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The cerebral cortex is folded in on itself to produce ridges known as gyri (singular: gyri; plural: gyrus) and valleys in the folds of the cerebral cortex known as sulci (singular: sulci; plural: sulcus). As mentioned previously in this text, gray matter is where processing and regulating of information occurs in the CNS, so it makes sense that the cerebral cortex, where our highest level of cognition occurs, is composed of gray matter. Gray matter is also found in some structures beneath the cortex (i.e., subcortical structures), such as the cerebellum, and the spinal cord.

Demyelinating Illnesses

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Certain diseases attack and break down the myelin sheath of white matter (Figure 11–8A–C). These are known as demyelinating illnesses. The damage to the myelin sheath wrought by these diseases is termed demyelination. Demyelination disrupts the potential of neurons to conduct neural impulses. As the myelin is broken down, the nerve fiber is unable to maintain function. Some demyelinating diseases target myelin in the CNS, while others target myelin within the PNS. Degradation of the myelin inhibits appropriate neural functioning by disrupting communication between different areas of the CNS or PNS, or both. Amyotrophic lateral sclerosis and multiple sclerosis are two demyelinating diseases of the CNS. Guillain-Barré and Charcot-MarieTooth disease are two diseases that affect myelin in the PNS. Speech-language pathologists spend a great deal of time working with individuals with disabilities and differences in communicative, cognitive, and swallowing ability due to demyelinating illnesses.

FIGURE 11–8.  A. Myelinated neuron. B. Demyelination of an axon. C. Degeneration of the axon towards the soma resulting in nerve lesion.

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There are deeper divisions in the cerebrum of the brain, in addition to the relatively shallow sulci of the cortex, that are referred to as fissures.

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Gyri, sulci, and the fissures between divisions of the cerebrum are important landmarks for understanding the anatomy of the brain. Sections of this chapter that follow concerning the cerebral hemispheres and the cerebral lobes will delve into the information concerning these structures and their importance.

Between the inner surface of the skull and the surface of the brain and spinal cord are three layers of tissue that are the cerebral meninges (Figure 11–9). As the cerebral meninges envelops the brain and spinal cord, it is important to note that the entire CNS is enclosed in these three layers. In order of most superficial to most deep, these are the dura mater, arachnoid mater, and pia mater: n

The most superficial of the cerebral meninges is the dura mater. The dura mater (which means tough mother in Latin) is a protective, thick, and fibrous tissue layer that enwraps the brain and spinal cord (Figure 11–9).

n The

arachnoid mater is deep to the dura mater (Figure 11–9) and is far more delicate than the dura mater. The arachnoid mater is highly vascular, meaning it contains a large number of blood vessels. It is so named due to the spider-web–like system of blood vessels that are visible within this layer. As the arachnoid mater is highly vascular, it plays a large role in supplying blood to the surface of the brain by the many blood vessels that it contains.

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The deepest meningeal layer is the pia mater (which is Latin for gentle mother) (Figure 11–9). This is the most fragile meningeal layer. The pia mater closely follows the surface of the brain and spinal cord and contains blood vessels from the arachnoid mater that are passing to and from the surface of the brain. In this way, the arachnoid mater and the pia mater are important in that they house the blood vessels, providing nourishment to the surface of the brain. At times, the arachnoid mater and the pia mater are referred to as a single unit known as the leptomeninges.

FIGURE 11–9.  Cerebral meninges.

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Infection and inflammation of the meningeal layers are referred to as meningitis, a serious and potentially fatal condition if left untreated. See an infected and inflamed dura mater being retracted from the leptomeninges to expose the arachnoid mater in Figure 11–10.

Ventricular System

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The ventricular system is an interconnected series of fluid-filled cavities within the brain and also between the arachnoid mater and pia mater that functions to remove waste from the brain and deliver nutrients (Figure 11–11) (Iliff et al., 2012). It does this by manufacturing and circulating a clear fluid known as cerebrospinal fluid. The primary anatomy of the ventricular system consists of four cavities or ventricles that house and manufacture cerebrospinal fluid. These are the two lateral ventricles, the third ventricle, and fourth ventricle (Figure 11–11):

FIGURE 11–10.  Head autopsy revealing dura mater. Source: CDC Public Health Image Library/Dr. Edwin P. Ewing, Jr. (1972).

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FIGURE 11–11.  Cerebrospinal fluid ventricles.

n The

lateral ventricles are two symmetrical and large, C-shaped cavities beneath the cerebrum that at any moment contain most of the cerebrospinal fluid within the ventricular system (Figure 11–11). The lateral ventricles contain the tissue that produces most of the cerebrospinal fluid in the ventricular system known as choroid plexus.

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The lateral ventricles are connected to one another via a medial and inferior connection that is the foramen of Monro (Figure 11–11).

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The foramen of Monro leads to the much smaller and medial third ventricle (Figure 11–11).

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The fourth ventricle is associated with the brainstem and is at the level of the pons and medulla and anterior to the cerebellum. The passage between the third ventricle and the fourth ventricle is the cerebral aqueduct (Figure 11–11).

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Cerebrospinal fluid is produced in the lateral ventricles and flows from there inferiorly to to the third and fourth ventricles. From the fourth ventricle, cerebrospinal fluid flows to the subarachnoid space, which is between the arachnoid mater and the pia mater (Figure 11–11).

n

By floating the CNS in cerebrospinal fluid within the ventricles and subarachnoid space, the ventricular system helps cushion the brain from trauma. Primarily, it functions to generate and circulate cerebrospinal fluid that delivers nutrients to the brain and removes waste (Iliff et al., 2012).

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Xie et al. (2013) found that this process of waste removal by the ventricular system primarily occurs during sleep. When a person goes to sleep, the interstitial spaces between cells of the brain are allowed to expand, which facilitates the flushing of waste products away from the cells

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Hydrocephalus and Cerebrospinal Fluid Shunts

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A buildup of too much cerebrospinal fluid in the ventricles is hydrocephalus. This condition can be created by excessive production of cerebrospinal fluid, failure to reabsorb and dispose of cerebrospinal fluid, or an obstruction between the ventricles (National Institute of Neurological Disorders and Stroke, 2020). Hydrocephalus is a dangerous condition. As abnormal amounts of cerebrospinal fluid build up in the ventricles, the brain is compressed between the expanding ventricles and the walls of the skull. This can cause serious medical complications including death (Figure 11–12). Hydrocephalus can be congenital or acquired through trauma to the brain. Infants with genetic abnormalities, birth defects, infection, or trauma before or during birth are at risk of developing hydrocephalus (National Institute of Neurological Disorders and Stroke, 2020). In infants, untreated hydrocephalus leads to an enlarged skull. This is due to the cartilaginous nature of the skull at this early stage of development that can expand to accommodate heightened levels of intracranial pressure from hydrocephalus. Untreated, hydrocephalus can be fatal, but medical treatment is effective and most often involves the placing of an intraventricular shunt or cerebrospinal fluid shunt. An intraventricular shunt is essentially a surgically placed tube in the body that runs to another location within the body, allowing excess cerebrospinal fluid to exit the ventricles and be disposed of (Figure 11–12). Those recovering or suffering from hydrocephalus benefit from the work of many rehabilitation and educational professionals, including speech-language pathologists.

FIGURE 11–12.  Intraventricular shunt. An intraventricular shunt is a tube that originates in the lateral ventricle within the brain. It travels under the skin, usually along the neck, and terminates in the chest or abdomen. It allows excess cerebrospinal fluid to be reabsorbed outside of the skull.

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by cerebrospinal fluid. Sleep is required in that it allows the ventricular system to appropriately cleanse our brains of waste. Xie et al. (2013) provided the first evidence of exactly why our brains function poorly without sleep and why, if completely deprived of sleep, a human cannot survive. n

When cerebrospinal fluid has circulated through the brain and has delivered nutrients and picked up waste from the brain, it is then drained from the subarachnoid space into the venous system to be disposed of by the body.

Cerebral Hemispheres A deep groove runs anterior to poster through the cerebrum, dividing it into left and right halves known as the cerebral hemispheres (Figure 11–13). This front-to-back fissure creating the cerebral hemispheres is the longitudinal fissure, and it runs the length of the cerebrum: n

In the course of maturation and development, an infant’s brain begins the process of hemispheric specialization in which each cerebral hemisphere becomes generally responsible for different cognitive and motor functions.

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The cerebral hemispheres become responsible for motor control to the contralateral side of the body and for receiving somatosensation from the contralateral side of the body. This arrangement where each cerebral hemisphere controls the opposite side of the body is known as contralateral innervation: n

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In short, the right cerebral hemisphere becomes responsible for generating signals for volitional movement of the left side of the body while receiving and processing sensory information coming up to the brain from the left side of the body. The left cerebral hemisphere becomes responsible for generating signals for volitional movement of the right side of the body while receiving and processing sensory information being transmitted from the right side of the body to the left cerebral hemisphere.

FIGURE 11–13. Cerebral hemispheres. Reproduced with permission from Anatomage.

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Although the cerebral hemispheres have functions they each specialize in, it is wrong to think that the cerebral hemispheres function independently and in isolation from each other. The cerebral hemispheres perform their operations alongside and with help from one another, working in tandem, and this cooperation is made possible by a white matter pathway that connects the two cerebral hemispheres known as the corpus callosum (Figure 11–14). n The corpus callosum is located deep within and at the base of the longitudinal fissure. The corpus callosum is the largest white matter pathway connecting the cerebral hemispheres and allowing for communication between the left and right cerebral hemispheres. n In most individuals, the left cerebral hemisphere is dominant for language, meaning that most of our language abilities are usually housed within the left cerebral hemisphere. n Most individuals are right-handed. Because of contralateral innervation of the body, the left cerebral hemisphere is responsible volitional motor control to the right side of the body. Therefore, in most individuals, the left cerebral hemisphere is also responsible for control of their dominant hand for writing (the right hand) in addition to being dominant for language. n Although the right cerebral hemisphere has many important functions, it is not dominant for language. Even in left-handed individuals, the left cerebral hemisphere usually houses language or a greater part of it. n The left cerebral hemisphere is usually assumed to be synonymous with language dominance, though that is not necessarily always the case. Likewise, the right cerebral hemisphere is usually assumed to be synonymous with being nondominant for language. Right Cerebral Hemisphere.  Due to the limits of imaging technology in the past and the comparative ease of studying the function and deficits of the left cerebral hemisphere, most of the history of the study of the brain has been the study of the left cerebral hemisphere. Due to a lack of understanding of the importance of the right cerebral hemisphere, this 50% of the mass of cerebrum was previously disregarded as being relatively unimportant. Only within the previous 40 or 50 years has the study of the right cerebral hemisphere and our understanding of the right cerebral hemisphere expanded to begin to shed light on some of the most interesting deficits in neurology.

FIGURE 11–14.  Corpus callosum. Reproduced with permission from Anatomage.

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Although the right cerebral hemisphere plays a limited role in language, it has significant responsibilities for the process of communication. It is important to recall that communication involves not only your language (the words you use) but the prosody with which you speak your words. Prosody includes the changes in tone, rate, and intensity we use when we speak that give our spoken words an emotional component. Communication also involves your body language, facial expressions, and any accompanying gestures. These are all highly meaningful aspects of communication that accompany your use of language, but they are not language, they are nonlinguistic forms of communication. The right cerebral hemisphere specializes in these nonlinguistic forms of communication: n

These nonlinguistic forms of communication (prosody, facial expression, body language, gesture) are important because these are aspects of communication that contain a great deal of the emotional content of a person’s communication.

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As the right cerebral hemisphere is responsible for these nonlinguistic aspects of communication, the right cerebral hemisphere is very important to the expression of emotion.

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However, the right cerebral hemisphere is also important to the comprehension of the emotional content of other’s communication. The right cerebral hemisphere processes the meaning of body language, facial expression, gesture, and prosody of others.

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As most people communicate using their emotions a great deal, the ability to understand the emotional expression of others and to be able to express emotion effectively oneself is highly important to effective communication. When a person has damage or disfunction of the right hemisphere and is less capable of expressing their emotions and/or less capable of comprehending the emotional content of the expression of others, this can inhibit a person’s ability to communicate effectively.

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Deficits in the realm of using nonlinguistic forms of communication for expression or understanding the meaning of nonlinguistic information embedded within the expression of others often creates difficulties in the realm of social interactions.

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Speakers often use prosody, facial expression, or another nonlinguistic signals to indicate the presence of figurative language. Figurative language is used by speakers to overly a layer of meaning to their spoken words that embellishes, adds to, or even contradicts the meaning of the spoken words themselves. Some examples of figurative language are metaphor, hyperbole, idioms, or sarcasm. As a functional right hemisphere is required for the production of figurative language and for the comprehension of the figurative language of others, individuals with damage to the right hemisphere lose these abilities.

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Due to the loss of figurative language, those who have experienced right cerebral hemisphere damage are often overly restricted to the literal interpretation of other’s utterances. One can imagine the difficulty one would encounter in social situations without the ability to determine if a speaker is communicating literally or figuratively.

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The right cerebral hemisphere plays a large role in the ability to use appropriate facial expressions for expression of emotion as well as in the understanding of the facial expressions of others:

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Individuals who have experienced damage to the right cerebral hemisphere often display deficits in the ability to perceive faces and recognize familiar faces (Luria, 1973).

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Prosopagnosia is the deficit in the ability to recognize familiar faces. It is also commonly known as face blindness. A severe case of prosopagnosia can manifest in an individual being unable to recognize family members or close loved ones. They may not even be able to recognize

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their own face and will struggle with recognizing the meaning of facial expressions, which as noted before, is where a great deal of the emotional content of human communication is located. For the person with right cerebral hemisphere damage leading to prosopagnosia, this often contributes to difficulties in social interactions. n

Due to their difficulties expressing emotion via facial expression and prosody, those who have experienced damage to the right cerebral hemisphere are often judged by their speaking partners as having a monotone and emotionless voice and a neutral expressionless face. However, this lack of emotional expression due to a loss of prosody and facial expression does not reflect the true emotional state of the speaker. Clinicians and families of these patients must be careful to explicitly inquire into their emotional well-being and emotional state to be able to more correctly gauge the emotional state of the patient.

The right cerebral hemisphere also plays a role in the processing of nonspeech environmental sounds: n

Due to this, those with damage to the right cerebral hemisphere have been known to lose their ability to interpret the meaning of environmental sounds such as a toilet flushing, a car starting, or the sound of typing (Joseph, 1988). These individuals can specifically lose the ability to comprehend the meaning of environmental sounds while retaining their ability to process and comprehend prosody. This condition is revisited later more specifically in discussions of the auditory cortices.

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Macrostructure processing refers to the ability to recognize smaller details and, perceiving how many smaller details fit together, arrive at an understanding of the whole. An example would be a person’s ability, when looking at an animal, to perceive the many individual characteristics of the animal to arrive at a correct perception of the animal as a whole.

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Patients with right cerebral hemisphere damage often have deficits in macrostructure processing. These patients often are overly anchored to the smaller details and display an inability to perceive how details are related to generate a perception of the whole. Family members of these patients will often refer to their loved ones and being “unable to see the forest for trees.”

The right cerebral hemisphere also plays a large role in visuospatial processing. In short, visuospatial processing is the ability to determine the spatial relationships among objects perceived visually. Some examples of visuospatial skills are the visual perception of depth, movement, distance, shape, figure-ground, and the ability to localize targets in space (Joseph, 1988). Visuospatial skills are also very important to understanding where one’s own body parts are in space and how to navigate one’s body through space and the world. The right cerebral hemisphere is integral to regulating different levels of attentional abilities. The right hemisphere is known to play a large role in sustained attention and selective attention: n

As mentioned previously, sustained attention is the cognitive ability to hold one’s attention on a single stimulus for an extended period of time. Anytime you focus on attending to a speaker in a classroom, you are employing sustained attention ability.

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Selective attention is the cognitive ability to hold one’s attention on a single stimulus while not attending to competing or irrelevant stimuli. In other words, anytime there is a distraction, this is the cognitive ability you use to ignore the distraction and focus on the meaningful stimuli.

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The right cerebral hemisphere also allows for the processing of what is known as macrostructure, or gestalt:

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Those with damage to the right hemisphere often show deficits in both of these levels of attention. They struggle to hold their attention on any stimulus for any period of time and are extremely susceptible to having their attention broken by competing stimuli.

Left Cerebral Hemisphere.  Whereas study of the right hemisphere was almost nonexistent for much

of the history of neuroscience, the discovery that language is housed in the left cerebral hemisphere prompted decades of study into the function of the left cerebral hemisphere that began in the late 1800s. This early research into the left hemisphere beginning in the 1800s and through the 1950s largely involved deriving knowledge of the function of the brain from the practice of lesion localization. Lesion localization is when a pathologic lesion is observed in the brain, for instance a stroke, and the clinical deficits a person is displaying are then attributed to that part of the brain affected by the lesion. Before neuroimaging technology existed, doctors were restricted to documenting the deficits of their patients, and when those patients died, an autopsy would be performed to see what part of the brain was damaged. In a best-case scenario, the location of the lesion seen in autopsy would be responsible for the patient’s observed deficits. Then doctors could infer that the area of ability in which the deficits were displayed was the primary function of that particular location in the brain that experienced the lesion. Paul Broca and Carl Wernicke’s research revealing that the left hemisphere was the seat of language in the brain began a rush by scientists and doctors in exploring the anatomy of the brain in this way: n

Paul Broca’s research indicated that the left inferior and posterior frontal lobe was an area primarily responsible for locating words for the expression of intended meaning. In short, this is the part of your brain that helps you find the words to express the meaning of what you want to say. His major study documenting this find was published in 1861.

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The area located in the left frontal lobe that Broca asserted was responsible for expressive language is now referred to as Broca area (Figure 11–15).

FIGURE 11–15.  Left cerebral hemisphere. Reproduced with permission from Anatomage.

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Individuals who have suffered damage to Broca area, most often due to stroke, usually know the meaning that they want to communicate in words, but they struggle to find the words representing their thoughts.

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After Paul Broca’s findings were published, Carl Wernicke then localized the auditory reception of language to the medial portion of the superior gyrus of the temporal lobe in the left hemisphere.

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This area that Carl Wernicke identified as playing a primary role in auditory receptive language is now known as Wernicke area (Figure 11–15).

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In short, Wernicke area is responsible for interpreting spoken language heard by an individual and allowing that individual to derive meaning from those spoken words they have heard.

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Damage to Wernicke area produces a unique set of deficits known as Wernicke aphasia. Those with Wernicke aphasia struggle to understand the speech of others, their own expressive language is often meaningless and tangential, and they usually struggle to understand they are suffering from any language deficits at all.

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Coursing between Broca area and Wernicke area is a large white matter pathway known as the arcuate fasciculus that connects these two areas (Figure 11–16):

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The arcuate fasciculus allows words received and processed in Wernicke area to be transmitted anteriorly to Broca area for direct repetition. Damage to the arcuate fasciculus creates a condition known as conduction aphasia. Individuals with conduction aphasia have deficits in the realm of direct repetition of language they hear.

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Near where the parietal, temporal, and occipital lobes meet just posterior to Wernicke area is an area known as the angular gyrus (Figure 11–15). Whereas Wernicke area is responsible for the reception of auditory language, the angular gyrus is important to the reception of visual language, such as reading written language and sign language.

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All these language-specific areas of the left cerebral hemisphere (Broca area, Wernicke area, arcuate fasciculus, and angular gyrus) are together referred to as the zone of language.

FIGURE 11–16.  Arcuate fasciculus. Reproduced with permission from Anatomage.

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Conduction Aphasia Conduction aphasia is categorized as a fluent type of aphasia. Individuals with conduction aphasia usually display relatively intact verbal expression and relatively intact auditory reception of language but have significant deficits in the realm of language repetition. A person with severe conduction aphasia will struggle to repeat even a short two- to three-word utterance. Conduction aphasia is usually interesting to students new to speech pathology because it illustrates a seeming paradox. This false paradox is that those who display conduction aphasia can understand the words they hear spoken to them but cannot repeat those words they have heard. This is usually the first time that students have considered that the comprehension of language, which takes place at Wernicke area, is indeed a separate skill from the repetition of language. However, despite being unable to transmit words from Wernicke area along the arcuate fasciculus to Broca area for verbal repetition, those with conduction aphasia can verbally express the meaning of the language they hear, though in their own words. This is due to the combination of largely intact auditory comprehension of language that enables them to understand the language they hear, and their usually largely intact expressive language ability that allows them to find their own words to paraphrase the meaning of the language they have heard. For example, if asked to repeat the sentence, “We walked on the beach and found seashells,” the person with conduction aphasia would struggle to repeat this sentence verbally. However, if asked the meaning of the sentence, the person may be able to offer their own correct interpretation of the meaning, such as “At the beach we were walking and finding seashells.”

➤ Chapter Summary The cells that make up the nervous system are divided into two basic categories: neurons and neuroglia. Neurons are cells of the nervous system responsible for electrochemically transmitting and processing information. Neuroglia are several types of nervous system cells that act to provide important structural and physiological support to neurons but are not involved in transmitting or processing information. There are three basic divisions of neurons: sensory neurons, motor neurons, and interneurons. Interneurons are responsible for conjoining neurons to each other within the same area of the brain. Motor neurons are responsible for transmitting impulses of motor movement. Sensory neurons are responsible for transmitting sensory information. A neuron is made up of a cell body/soma, dendrites, and an axon. The soma is the portion of the neuron that contains the nucleus. Dendrites are projections that extend from the soma and synapse with axons of other neurons in order to receive information from the axons of these other neurons. The axon is a long projection from the nucleus that transmits information from the soma to the dendrites of other neurons. Motor and sensory neurons have axons wrapped in a white substance made of proteins and fat that is known as myelin. Myelin is a protein and fatty substance that forms electrical insulation for axons. It is the myelinated axons of sensory neurons that largely constitute the sensory pathways

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in the nervous system, and it is the myelinated axons of motor neurons that largely constitute the motor pathways in the nervous system. Myelinated neurons, such as motor and sensory neurons, are white matter; unmyelinated neurons such as interneurons, are gray matter. A neuron’s axon divides into terminal buttons before connecting to dendrites of other neurons. This point of connection between terminal buttons and dendrites is the synapse and is the point of connection and communication between neurons. Synaptic transmission is the process of communication between neurons across synapses. There are two neuroglial cells that are responsible for the production of myelin: Schwann cells and oligodendrocytes. Schwann cells produce myelin on axons within the PNS. Oligodendrocytes produce myelin on axons within the CNS. The neuroglial cells, astrocytes, provide structural support for neurons in the intercellular space between neurons in the CNS and function to maintain homeostasis in the CNS, help establish the blood–brain barrier, and can release additional energy to neurons if needed. The smallest category of neuroglia, microglia, are the strongest line of immune defense of the CNS. The nervous system is composed of two major divisions: the CNS and the PNS. The central nervous system (CNS) is composed of the brain and the spinal cord. The peripheral nervous system (PNS) is composed of the sensory and motor nerve tracts that course between the CNS and the rest of the body. The brain is part of the CNS and has three major divisions: the cerebrum, the brainstem, and the cerebellum. The cerebrum is the most superior section of the brain and is where the highest and most complex level of cognition, language, and most skilled motor movement is generated. The most superficial tissue of the cerebrum is a thin layer known as the cerebral cortex. The cerebral cortex is the part of the brain where the highest-level cognition and sensory/motor processing occurs. Between the inner surface of the skull and the surface of the brain and spinal cord are three layers of nutritive and protective tissue that are the cerebral meninges. In order of most superficial to most deep, these are the dura mater, arachnoid mater, and pia mater. Infection and inflammation of the meningeal layers are referred to as meningitis. The ventricular system is an interconnected series of cavities within the brain and also between the arachnoid mater and pia mater that produce and contain cerebrospinal fluid that circulates and functions to remove waste from the brain and deliver nutrients. The primary anatomy of the ventricular system consists of four cavities or ventricles that house and manufacture cerebrospinal fluid. These are the two lateral ventricles, the third ventricle, and the fourth ventricle. The lateral ventricles contain the tissue that produces most of the cerebrospinal fluid in the ventricular system known as choroid plexus. When cerebrospinal fluid has circulated through the brain and has delivered nutrients and picked up waste from the brain, it is then drained from the subarachnoid space into the venous system to be disposed of by the body. A buildup of too much cerebrospinal fluid in the ventricles is hydrocephalus. A deep groove known as the longitudinal fissure divides the cerebrum into left and right cerebral hemispheres. The two cerebral hemispheres are connected and communicate with one another via a large bundle of white matter known as the corpus callosum. Due to contralateral innervation, the left cerebral hemisphere is responsible for motor control to the right side of the body, and the right cerebral hemisphere is responsible for motor control to the left side of the body.

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In most individuals, the left cerebral hemisphere is dominant for language meaning that most of our language abilities are usually housed within the left cerebral hemisphere. The right cerebral hemisphere specializes in nonlinguistic forms of communication such as prosody, facial expression, body language, and gesture. As a great deal of the emotional content of communication exists in these nonlinguistic forms of communication, the right cerebral hemisphere is important to the comprehension of the emotional content of other’s communication and is also important to the appropriate expression of emotion. The right cerebral hemisphere also plays a large role in facial recognition. Prosopagnosia is the deficit in the ability to recognize familiar faces. It is also commonly known as face blindness. The right cerebral hemisphere also plays a role in the processing of nonspeech environmental sounds. The right cerebral hemisphere allows for the processing of what is known as macrostructure, or gestalt. Macrostructure processing refers to the ability to recognize smaller details and, perceiving how many smaller details fit together, arrive at an understanding of the whole. The right cerebral hemisphere also plays a large role in visuospatial processing. Visuospatial processing is the ability to determine the spatial relationships among objects perceived visually. The right hemisphere is known to play a large role in sustained attention and selective attention. Lesion localization is when a pathologic lesion is observed in the brain, for instance a stroke, and the clinical deficits a person is displaying are then attributed to that part of the brain affected by the lesion. This was the primary method used by early scientists exploring the function of the different areas of the brain. Paul Broca’s research indicated that the left inferior and posterior frontal lobe was an area primarily responsible for locating words for the expression of intended meaning. The area located in the left frontal lobe that Broca argued was responsible for expressive language is now referred to as Broca area. Carl Wernicke identified an area largely responsible for the auditory reception of language that was on the medial portion of the superior gyrus of the temporal lobe in the left hemisphere. This became known as Wernicke area. Coursing between Broca and Wernicke areas is a large white-matter pathway known as the arcuate fasciculus. The arcuate fasciculus allows direct repetition of heard language. All these language-specific areas of the left cerebral hemisphere (Broca area, Wernicke area, arcuate fasciculus, and angular gyrus) are together referred to as the zone of language.

➤ References Barres, B. A. (2008). The mystery and magic of glia: A perspective on their roles in health and disease. Neuron Perspective, 60, 430–440. Iliff, J. J., Wang, M., Liao, Y., Plogg, B. A., Peng, W., Gundersen, G. A., . . . Nedergaard, M. (2012). A paravascular pathway facilitates CSF flow through the brain parenchyma and the clearance of interstitial solutes, including amyloid B. Science Translational Medicine, 4(147). Joseph, R. (1988). The right cerebral hemisphere:

Emotion, music visual-spatial skills, body-image, dreams, and awareness. Journal of Clinical Psychology, 44(5), 630–673. Koehler, R., Roman, R., & Harder, D. (2008). Astrocytes and the regulation of cerebral blood flow. Trends in Neuroscience, 32(3), 160–169. Lee, Y., Morrison, B., Li, Y., Lengacher, S., Farah, M. H., Hoffman, P. N., . . . Rothstein, J. D. (2012). Oligodendroglia metabolically support axons and contribute to neurodegeneration. Nature, 487, 443–448.

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Xie, L., Kang, H., Xu, Q., Chen, M. J., Liao, Y., Thiyagarajan, M., . . . Nedergaard, M. (2013). Sleep drives metabolite clearance from the adult brain. Science, 342(6165), 373–377.

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Luria, A. (1973). The working brain: An introduction to neuropsychology. Basic Books. National Institute of Neurological Disorders and Stroke. (2020). Hydrocephalus fact sheet.

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➤ Learning Outcomes Upon completion of this chapter, students will be able to: n

Identify the major lobes of the cerebrum and the specialized areas within these in regard to speech, language, and cognition.

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Explain the nature and function of subcortical structures such as the basal ganglia, cerebellum, and thalamus.

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Understand the major division of the brainstem and general function of each division.

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Understand the general location, function, and anatomy of the different portions of the peripheral nervous system.

➤ The Lobes of the Cerebral Hemispheres In addition to the longitudinal fissure, two important landmarks that divide the cerebrum into major divisions are the lateral sulcus and the central sulcus (Figure 12–1): n

The central sulcus runs coronally across the medial portion of the cerebrum (Figure 12–1).

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Intersecting the base of the central sulcus is the lateral sulcus, which is also known as the Sylvian fissure. The lateral sulcus courses from the anterior, inferior, of each cerebral hemisphere and runs superiorly and posteriorly past the base of the central sulcus before terminating (Figure 12–1). 393

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FIGURE 12–1.  Lobes of the cerebrum. Reproduced with permission from Anatomage.

Whereas the longitudinal fissure divides the brain into left and right cerebral hemispheres, the lateral and central sulcus create important divisions within the cerebral hemispheres. These two sulci play important roles in dividing each of the cerebral hemispheres into major functional units known as the lobes of the cerebrum: n

The central sulcus creates the point of division between the frontal lobes and parietal lobes in each cerebral hemisphere (Figure 12–1). n As the lateral sulcus courses along the side of each cerebral hemisphere, it divides the base of each frontal lobe and parietal lobe from each temporal lobe (Figure 12–1). There are four lobes of the cerebrum in each of the two hemispheres: frontal, parietal, temporal, and occipital (Figure 12–1). Each of these paired lobes has a specific function and purpose and houses specialized areas within.

Frontal Lobes The anterior-most lobes of the cerebrum are the frontal lobes (Figure 12–1). The frontal lobes are extremely important to cognitive functions such as attention, memory, decision-making, and executive functioning. The frontal lobes also have important functions in regard to motor movement, speech, and language: n

Perhaps most important to the speech-language pathologist is the left frontal lobe that houses Broca area in the inferior posterior portion which is the primary area for expressive language. n The anterior-most portion of the paired frontal lobes is known as the prefrontal cortex. The prefrontal cortex is responsible for higher level cognitive skills such as decision-making, problem-solving, as well as executive functioning, initiation of movement, and inhibition of inappropriate social impulses. n Volitional and skilled motor activity (body movement) also originates in the frontal lobes. The ability of the brain to initiate movement and the ability to put together plans for body 394

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movement (efferent signal or motor plans) are housed in the frontal lobes. One of the primary areas responsible for volitional movement of the body is the primary motor cortex, also sometimes known as the motor strip: n The primary motor cortex is the posterior-most gyrus of both frontal lobes. n The primary motor cortex issues plans for volitional movement to be transmitted to the body for execution. n Due to contralateral innervation of the body for volitional movement, the right primary motor cortex issues plans of volitional movement to the left side of the body, and the left primary motor cortex issues plans of volitional movement to the right side of the body. n Within the primary motor cortex, those body parts that are capable of more elaborate, complex, and fine motor movement require more cortical surface area to be devoted to the motor control of these body parts. Those body parts that are capable of less elaborate, complex, and fine motor movement usually require less cortical surface area of the primary motor cortex dedicated to their control. For instance, body parts involved in speech that have to be moved very rapidly and with precision, such as the lips and tongue, are controlled by a greater amount of cortex within the primary motor cortex as opposed to, say, a portion of the back that moves very little in comparison. n A visual illustration of the varying amounts of cortex within the primary motor cortex dedicated to different portions of the body is known as the motor homunculus (Figure 12–2). Homunculus is a Latin word for little man.

Parietal Lobes

FIGURE 12–2.  Sensory homunculus and motor homunculus.

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Posterior to the frontal lobes are the parietal lobes (Figure 12–1). The parietal lobes are responsible for receiving and processing signals of body sensation, also known as somatosensation. Somatosensation

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is the group of sensory modalities originating from the body responsible for body sensations such as taction (sensation of touch), nociception (sensation of physical pain), and proprioception (sensation of the location of one’s body in space): n

Somatosensation arises from sensory receptors in the muscles, joints, and skin which generates afferent signals that are transmitted via the peripheral nervous system to the brainstem and spinal cord to ultimately arrive at the primary sensory cortex.

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The most anterior gyrus of the parietal lobes is the primary sensory cortex that is also known as the sensory strip.

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The primary sensory cortex receives and begins processing the somatosensation from the body. n As the primary motor cortices (left and right) and the body display contralateral patterns of innervation, so does the primary sensory cortices. The left primary sensory cortex receives somatosensation from sensory receptors within the right side of the body, and the right primary sensory cortex receives somatosensation from sensory receptors in the left side of the body. n

Within the primary sensory cortex, more cortical surface area is dedicated to those body parts that have higher numbers of sensory receptors and are, therefore, more sensitive, such as the mouth and the hands. Furthermore, those body parts with fewer sensory receptors, which are therefore less sensitive, have less cortical surface area within the primary sensory cortex devoted to them, such as the knee and elbow.

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The visual illustration/map of this arrangement of the cortex within the primary sensory cortex representing the varying degree of somatosensory representation of portions of the body is the sensory homunculus (Figure 12–2).

Temporal Lobes The location of the temporal lobes is inferior to the frontal lobes and parietal lobes and anterior to the occipital lobes (Figure 12–1). The temporal lobes are most well known for their role in reception and processing of audition, the sensation of hearing: n

As previously mentioned, Wernicke area, which is responsible for the comprehension of spoken language of others, is located in the left temporal lobe, specifically on the posterior one third of the superior temporal gyrus.

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One of the most noteworthy bilateral functions of the temporal lobes is that they contain more memory than other lobes of the cerebrum. Much of this capability is due to an area within both temporal lobes that is central to memory capability known as the hippocampi (plural ; singular : hippocampus): n

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The hippocampi are located deep within the inferior curl of the temporal lobes. There is a left hippocampus within the left temporal lobe and a right hippocampus within the right temporal lobe. These are easily viewed on a coronal view of the brain (Figure 12–3). Hippocampus is Latin for “seahorse” due to the resemblance of this structure to that marine creature. The hippocampi are extremely important to memory in that they function to turn shortterm memory into long-term memory for storage that can be later retrieved and not simply discarded and forgotten. The role of the hippocampi in generating memory was not understood until doctors Scoville and Milner (1957) began performing surgeries to excise the medial portions of both temporal 396

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FIGURE 12–3.  Hippocampus on coronal section of brain. Reproduced with permission from Anatomage.

lobes of some patients with life-threatening temporal lobe seizures. These patients’ seizures were reduced or eliminated after surgery, but the doctors noted a severe unexpected outcome in that these patients lost the ability to generate new memories. One of these patients was known as Patient H.M. for decades, and much of what we understand now about how memory functions is due to this man’s willingness to engage in memory scientists throughout his life (Carey, 2008; Corkin 2002).

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Those individuals who have experienced damage to one hippocampus still retain some memory capability, but those who have bilateral damage to the hippocampus have profound deficits in the ability to remember new memories. Although surgeons now know to avoid removal of both hippocampi, if possible, there are still conditions that can create fairly isolated bilateral damage to the hippocampi, such as anoxia or possibly strokes. However, speech-language pathologists will have individuals with all types of memory deficit, and memory deficit–inducing diseases, on their rehabilitation caseload, in addition to those patients with bilateral hippocampal damage as described earlier. Most people who know of the hippocampi are aware of it due to Alzheimer disease. In the course of Alzheimer disease, the hippocampi are where degeneration is first observed to occur. This results in the hallmark symptom of Alzheimer disease — memory loss. The degeneration of the hippocampi can be viewed on those with Alzheimer disease and appears as a wide-open space in the hippocampi which was once a tight curl (Figure 12–4).

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Another feature of the temporal lobes is the primary auditory cortex. The primary auditory cortex is located posteriorly on the superior temporal gyrus and on the left temporal lobe is located posterior to Wernicke area.

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The role of the primary auditory cortex is to receive afferent signals of audition (hearing) from the ears. 397

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FIGURE 12–4.  Degeneration of brain in Alzheimer disease.

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The left primary auditory cortex receives afferent signals of speech sounds and transmits those signals posteriorly to be processed in Wernicke area, allowing for comprehension of the speech of others. n The right primary auditory cortex receives afferent signals from the ears representing environmental sounds and transmits those impulses to the area just posterior to it for processing and the interpretation of the meaning of these nonspeech sounds (Bhatnagar, 2008).

The Occipital Lobes The posterior-most lobes of the cerebrum are the occipital lobes that are located behind the parietal and temporal lobes (Figure 12–1). The primary function of the occipital lobes is visual processing: n

The occipital lobes receive afferent information from the retinas of the eyes at the primary visual cortex. The primary visual cortex is the posterior-most section of the occipital lobes. The portion of the primary visual cortex in the left occipital lobe receives afferent information concerning the right visual field from both eyes. The portion of the primary visual cortex in the right occipital lobe receives afferent information concerning the left visual field from both eyes. n Anterior to the primary visual cortex is the visual association cortex. This larger portion of each occipital is responsible for processing and interpretation of the afferent information received at the primary visual cortex. n In short, the visual association cortex is the part of the occipital lobe that allows a person to understand what they are seeing, whereas the primary visual cortex is more concerned with simply receiving afferent information from the eyes. n A lesion or damage to the primary visual cortex results in a state of blindness referred to as cortical blindness. Cortical blindness is a complete loss of vision due to damage to the cortex. n A bilateral lesion to the visual association cortex creates not a loss of vision but an inability to make sense of what is being visually perceived, known as visual agnosia. 398

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➤ Subcortical Structures Deep to the cortex is an area and a group of structures collectively referred to as the subcortex. Whereas the cortex is known for our highest-level reasoning and cognitive functions, the subcortex is responsible for more life-giving and involuntary functions. Some of these functions of subcortical structures include maintenance of homeostasis in the body, regulation of digestion, regulation of the heart and cardiovascular system (heartbeat, blood pressure, etc.), regulation of vegetative respiration, the presence of reflexes, and the refining and monitoring of volitional motor movement. Subcortical structures covered here include the brainstem, cerebellum, thalamus, basal ganglia, and limbic system.

The Brainstem The brainstem is responsible for basic life-giving, and therefore very important, functions. The brainstem along with the cerebellum are the oldest parts of the human brain and were present in our ancestors many millennia before we developed a cerebrum and higher level cognitive abilities: n

Moving inferiorly from the cerebrum, the brainstem occurs and then narrows into and becomes the spinal cord (Figure 12–5).

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Most somatosensory and efferent/motor pathways coursing between the cerebrum and the body pass through the brainstem.

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The brainstem has three primary divisions. From superior to inferior, they are the midbrain, the pons, and the medulla (Figures 12–5 and 12–6): n

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Beneath the thalamus and above the pons is the midbrain (Figures 12–5 and 12–6). Within the midbrain is the substantia nigra that functions to produce the necessary neurotransmitter dopamine. Beneath the midbrain and above the medulla is the pons (Figures 12–5 and 12–6).

FIGURE 12–5.  Brainstem in context. Reproduced with permission from Anatomage.

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FIGURE 12–6.  Brainstem. Reproduced with permission from Anatomage.

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The pons is the slightly rounded middle portion of the brainstem, and it is where the cerebellum connects to the brain. Beneath the pons and above the spinal cord is the medulla (Figures 12–5 and 12–6). Although it is quite small, the medulla is extremely important to body function in a number of ways. The medulla houses the respiratory center from which originates vegetative respiration. The medulla houses the swallowing central pattern generator from which originates the reflexive coordinated sequential movements of the pharyngeal swallow (Jean, 2001). Together the pons and the medulla house the masticatory central pattern generator from which originates the volitional but highly automatic motor movement of chewing (Lund & Kolta, 2006; Morquette et al., 2012). Motor neuron fibers coursing from the primary motor cortex responsible for transmitting impulses of volitional body movement cross within the medulla from one side of the body to the other side. This is known as pyramidal decussation. Pyramidal decussation creates the contralateral innervation of the body in which the right cerebral hemisphere controls volitional movement to the left side of the body, and the left cerebral hemisphere controls volitional movement to the right side of the body. A unilateral (one-sided) spastic weakness of the body is known as hemiparesis, whereas a unilateral spastic total paralysis is hemiplegia. It is due to the crossing over at the medulla of these descending motor neuron pathways (Figure 12–7), that a lesion above the medulla (e.g., a unilateral stroke in one of the cerebral hemispheres) will create a hemiparesis or hemiplegia in the side of the body contralateral (on the opposite side) to the lesion. In short, a stroke in the left cerebral hemisphere, being above pyramidal decussation, will cause hemiparesis or hemiplegia in the right side of the body, and vice versa. If the stroke occurs in the spinal cord below pyramidal decussation, then the hemiparesis or hemiplegia will be on the side of the body ipsilateral (on the same side) as the lesion. 400

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Within the midbrain, pons, and medulla exists a number of nuclei that are the reticular activating system. The reticular activating system includes important structures that together work to regulate the level of wakefulness or arousal (including the sleep/wake cycle) and other autonomic functions such as blood pressure and respiration (Seikel et al., 2010).

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The brainstem is also responsible for the generation of what are known as brainstem reflexes.

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reflex is a simple motor response generated by the brainstem or possibly spinal cord automatically (beneath the level of awareness) in response to incoming sensory stimuli. Reflexes allow a person to respond quickly to changes in their environment and thereby assist in ensuring survival. Reflexes allow the body to respond quickly to stimuli by not waiting for 401

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FIGURE 12–7.  Decussation of motor neurons at medulla. Source: Figure 1.35 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 54), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

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sensory stimulation indicating certain changes or danger to be transmitted all the way up to the cerebrum for processing and decision-making before initiating a physical response. n

When a baby is born it has no organized conscious thought or knowledge of the world into which it is born. Its entire existence hinges on the presence of reflexes that allow it to respond automatically to the environment and survive.

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Some examples of reflexes generated at the brainstem are the gag reflex and vestibulo-ocular reflex. The gag reflex normally occurs when parts of the posterior oral cavity or posterior pharyngeal wall are touched and causes contraction of the pharynx and closure of the airway to prevent aspiration and penetration. The vestibulo-ocular reflex causes the muscles of the eyes to contract and move the eyes in a direction opposite of changes in head position detected at the semicircular canals. In this way, the vestibulo-ocular reflex stabilizes visual gaze and allows a person to remain visually focused on something despite movement of the head.

➤ The Cerebellum The most easily recognizable subcortical structure is the cerebellum, as it hangs off the back of the brainstem and looks like a smaller version of the brain stuck between the brainstem and occipital lobe. In fact, the word cerebellum is Latin for “little brain.” The gross anatomy of the cerebellum is divided into anterior lobe, posterior lobe, and flocculonodular lobe (Figure 12–8). These three lobes are themselves divided into the right and left lateral cerebellar hemispheres with connecting medial tissue, the vermis, at midline (Figure 12–8). The lateral cerebellar hemispheres are similar to the cerebral hemispheres in that they are composed of a tightly folded superficial layer of gray matter with white matter pathways coursing beneath:

FIGURE 12–8.  Cerebellar anatomy.

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The paired lateral cerebellar hemispheres are connected to one another at midline by a structure of gray matter known as the vermis (Figure 12–8). The vermis receives somatosensory information via its connections with the pons to be transmitted to the cerebellar hemispheres.

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A sagittal slice of the cerebellum reveals what early anatomists thought to resemble a treelike pattern in the white matter projections within the cerebellum (Figure 12–9). Due to its botanical appearance, they named this the arbor vitae, which is Latin for “tree of life.”

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The only point of connection between the cerebellum and the rest of the central nervous system is at the pons. The cerebellum has three paired points of the connection with the pons known as the peduncles (Figure 12–10). These are known as the superior, middle, and inferior peduncles.

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The word peduncle is another Latin botanical term derived from the word pedunculus that refers to the stalk of a flower or the stalk of a fruit. Early anatomists perceived the cerebellum connected to the brainstem and resembling an apple hanging off the branch of a tree and thus applied the word peduncles to the connections between the cerebellum and the brainstem.

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The paired superior cerebellar peduncles (Figure 12–10) function to transmit outgoing information (refined motor plans) from the cerebellum to the thalamus destined ultimately for the cerebrum to be sent to the body for execution of movement.

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The paired middle cerebellar peduncles (Figure 12–10) largely receive motor signals in need of refining from the cerebrum to the cerebellar hemispheres.

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The paired inferior cerebellar peduncles (Figure 12–10) largely receive somatosensory information concerning body position and location of the body within space.

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Using the peduncles as input and output pathways, the cerebellum accomplishes its primary task as an error control device for volitional movement. The cerebellum monitors the volitional motor plans from the cerebrum and compares these motor plans to incoming somatosensation to ensure the motor plans are as coordinated and efficient as possible and free of errors.

FIGURE 12–9.  Sagittal prosection displaying structures of central nervous system. Reproduced with permission from Anatomage.

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FIGURE 12–10.  Cerebellar peduncles. Blue and black arrows illustrate incoming signals to the cerebellum, while the green arrow on the superior cerebellar peduncle illustrates outgoing signal from the cerebellum.

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Once plans for volitional movement have been assembled in the frontal lobes, those plans for volitional movement are transmitted inferiorly to the cerebellum through the middle cerebellar peduncles for monitoring and refinement. The cerebellum compares the intent of volitional motor plans from the cerebrum against the afferent somatosensory input being transmitted through the inferior cerebellar peduncles to the cerebellum indicating position of the body and location in space in an ongoing fashion. By comparing these two inputs, the cerebellum monitors the success of the motor plans in generating desired movements.

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If any inconsistencies exist between the intent of the movement and the likely outcome given the motor plan (i.e., an error in the motor plan), it alters that motor plan in terms of muscle tone, range of movement, and force of movement to avoid the error and more likely achieve the intended result. In short, the cerebellum monitors volitional motor plans and ensures that the body is appropriately executing those movements (Duffy, 2005) and that intended movements will achieve the desired result.

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These functions of monitoring and refinement of the volitional movement occur in an online, ongoing fashion with the cerebellum making needed adjustments to motor plans as needed based on incoming somatosensation from the body.

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The middle cerebellar peduncles connect each cerebellar hemisphere to the contralateral cerebral hemisphere. Due to this arrangement, each cerebellar hemisphere is responsible for receiving and monitoring and refining motor plans for volitional movement from the contralateral hemisphere (Duffy, 2005). Therefore, the left cerebellar hemisphere receives motor plans from the right cerebral hemisphere, and vice versa. Since each cerebral hemisphere generates motor

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plans for the opposite side of the body, each cerebellar hemisphere is responsible for monitoring and refining motor movement for the ipsilateral side of the body (Duffy, 2005). n

Because errors in volitional movement are more likely to occur on movements that are required to be executed with more speed, accuracy, and precision than volitional movements that can be executed with success slowly and with less precision, the cerebellum is far more involved in ensuring the appropriate and efficient execution of fast and precise motor movement.

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The volitional motor movement that is executed with great speed and precision by most individuals almost constantly are those movements that create speech. The ultimate outcome of appropriate cerebellar activity on the act of speech is the rapid, smooth, and efficient movement of the articulators from one articulatory position to the next as different phonemes are produced. In fact, these movements of the articulators become so efficient as they move from position to position during speech that the phonemes being produced in some small ways blend into one another. This is known as coarticulation.

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The speech-language pathologist must be aware of the function of the cerebellum and the result of impaired cerebellar function. With a decrease in cerebellar function, errors in tone, force, and range of movement of the articulators during speech become more likely, and appropriate coarticulation becomes less possible. This increase in errors often causes the speaker to slow their speech and, in doing so, the speaker often loses appropriate coarticulation. The speech disorder arising from cerebellar disfunction is ataxic dysarthria.

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Ataxic dysarthria can be a presenting symptom of cerebellar disease because, for most individuals, speech is the fastest and most precise motor activity executed in their daily lives for which they require normal cerebellar function.

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The cerebellum also contributes to balance and equilibrium. Hence, with cerebellar pathology, impaired balance and equilibrium are often present.

➤ The Thalamus

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All afferent/sensory pathways, except for the olfactory pathway, coalesce into the thalamus as they course superiorly through the CNS. From the thalamus, these afferent pathways fan out into the cerebrum to each deliver different sensory information to different areas of the cerebrum for processing. Due to this function, the thalamus is known as a neurological relay station for afferent/sensory information.

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For instance, afferent information concerning audition from the cochlea, after it is received at the brainstem, will pass through the thalamus before being sent superiorly to the primary auditory cortex. Similarly, afferent information concerning somatosensation will pass superiorly through the spinal cord, brainstem, and to the thalamus before being directed to the primary sensory cortex.

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The thalamus also receives refined plans of volitional movement from the cerebellum to be transmitted superiorly back to the cerebrum to be sent efferently to the body for execution of motor movement (Duffy, 2005).

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Superior to the brainstem and beneath the cerebrum are the paired right and left olive-shaped lobes of the thalamus (Figures 12–9 and 12–11):

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FIGURE 12–11.  Thalamus. Reproduced with permission from Anatomage.

➤ The Basal Ganglia The term basal refers to the bottom or base, while the word ganglia refers to a group of nerve cells that usually operate to accomplish a shared function. For the basal ganglia, this primary function is appropriate movement of the body via the facilitation of desired voluntary movement and inhibition of involuntary movement. However, the basal ganglia are also known to play roles in new motor learning, executive functioning, and behavior (Lanciego et al., 2012). Located laterally to the thalamus (Figures 12–12 and 12–13), the basal ganglia are actually a group of smaller structures working as a functional unit. These individual structures of the basal ganglia all have complex connections among themselves through much of the CNS: n

The four major subcortical structures of the basal ganglia are the putamen, globus pallidus, subthalamic nucleus, and substantia nigra (Figures 12–12 and 12–13).

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Together the putamen and globus pallidus are a unit of the basal ganglia known as the lentiform nucleus. With the addition of the caudate nucleus, these three structures comprise a unit of the basal ganglia known as the dorsal striatum.

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These four subcortical structures of the basal ganglia work in unison to accomplish the major functions of the basal ganglia.

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Deep within the midbrain is the dark structure known as the substantia nigra (Figure 12–12). A major role of the substantia nigra is the production of the neurotransmitter dopamine. Dopamine is essential to appropriate movement of the body and also plays a role in the pleasure/​reward consequences decision-making function of the basal ganglia (Balliene et al., 2007).

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Degeneration or damage to different structures or pathways within the basal ganglia can create a variety of movement disorders involving the lack of initiation of movement, loss of new motor learning, decreased voluntary movement, and increased involuntary movement. 406

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FIGURE 12–13.  Basal ganglia. Reproduced with permission from Anatomage.

Some pathological conditions that negatively affect the basal ganglia and are characterized by these motor difficulties are dystonia, Parkinson disease, Huntington disease, PANDAS, and Tourette syndrome. 407

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FIGURE 12–12.  Coronal view of substantia nigra and basal ganglia. Source: Figure 12.9 from Advance Review of Speech-Language Pathology: Preparation for the Praxis SLP and Comprehensive Examination, Sixth Edition (p. 511), by Celeste Roseberry-McKibbin, M. N. Hegde and Glen M. Tellis, 2024, Austin, TX: PRO-ED. Copyright 2024 by PRO-ED, Inc. Reprinted with permission.

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Basal Ganglia and Parkinson Disease In 1817, James Parkinson first identified Parkinson disease. He described six cases of an incipient loss of motor movement, which he then called the shaking palsy but which is now known as Parkinson disease (Parkinson, 1817/2002). Men are more likely to develop Parkinson disease than are women, and it is estimated that 10 million people worldwide are living with Parkinson disease. This disease is primarily associated with motor abnormalities characterized by rigidity, tremor, and slowness of volitional movement. Nonetheless, cognitive deficits present with this disease and can at times reach a degree of severity to be called dementia. With the formation of pathological protein deposits (Lewy bodies) in the pigmented cells of the substantia nigra in the midbrain, the neuropathologic process of Parkinson disease begins with the loss of these dopamine-producing cells within the substantia nigra. Once a large enough number of these cells have died, a substantial loss of dopamine is created. With the lack of dopamine, certain areas of the brain are unable to function properly. The first area to malfunction as a result of the lack of dopamine is the basal ganglia. The basal ganglia play a large role in regulating and refining motor movement, learning new sequences of motor movement, and maintaining postural reflexes. As such, the presenting symptoms of this disease are motoric in nature and involve the reduction of voluntary motor movements and the release of involuntary movements and postural abnormalities. The primary speech manifestation of Parkinson disease is hypokinetic dysarthria. The speech of those with hypokinetic dysarthria is often characterized by inaccurate articulation, breathy voice, increased rate, and, at times, stutter-like dysfluencies. Much of the work of the speech-language pathologist with these individuals focuses on minimizing these issues in speech to maximize the intelligibility of those with Parkinson disease.

➤ The Limbic System The limbic system is a set of subcortical structures generally located above the brainstem laterally to each side of the thalamus. The limbic system is deeply involved in regulating emotion, as well as behaviors such as feeding and mating, motivation, and emotional learning. Along with the brainstem and cerebellum, the limbic system is one of the oldest parts of the human brain: n

The major structures of the limbic system include the hypothalamus (Figures 12–12 and 12–14), the amygdala, and the mamillary bodies (Figure 12–14).

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Some scientists include the thalamus and hippocampus as part of the limbic system. As the limbic system deals heavily in emotion and as emotion experienced by a person is closely linked to their sensory experiences, it should be no surprise that the thalamus, through which passes all sensory information except for olfaction, can be considered part of the limbic system. Also, as memories are capable of eliciting strong emotion, and experiences producing strong emotion are most likely to create strong memories, it should be no surprise that the hippocampus, which encodes memory, can also be considered to be part of the limbic system.

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Deep within each temporal lobe is the almond-shaped amygdala that is involved in emotion. Specifically, the amygdala plays a role in the generation of negative emotions such as aggression, fear, anger, and anxiety. The amygdala also is involved in emotional 408

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FIGURE 12–14.  Limbic system. Reproduced with permission from Anatomage.

memory and fear conditioning. Fear conditioning is the result of an animal experiencing a stimulus and then experiencing a negative or painful response as a consequence to the presence of that stimulus and, in result, learning to fear the stimulus. The amygdala connects the memory or re-experiencing of a negative or painful experience to the elicitation of fear and anxiety. In short, the amygdala ensures we experience fear and anxiety in response to threatening stimuli. n

The more the amygdala is stimulated, the more sensitive it becomes to stimuli in the environment. The more sensitive the amygdala is, the more likely it is to be stimulated. This vicious cycle can eventually lead the amygdala to generate fear and anxiety in response to nonthreatening stimuli. This is one way in which a hyperactive amygdala can be involved in the manifestation of anxiety disorders.

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mammillary bodies (Figure 12–14) are small bodies of nuclei in front of the thalamus that share connections with the hippocampi and are involved in spatial and episodic memory (Dillingham, et al., 2015). Damage to the mammillary bodies, as in the case of a condition known as Korsakoff syndrome, which is induced by a lack of thiamine in the brain usually due to alcoholism, is known to create anterograde amnesia (Gold & Squire, 2006; Kril & Harper, 2012; Yoneoka et al., 2004). hypothalamus is located, as its name implies, just below the thalamus (Figures 12–12 and 12–14). The primary role of the hypothalamus is to regulate autonomic functions such as heart rate, blood pressure, urination and defecation, hunger, thirst, and sexual arousal. Below the hypothalamus is the pituitary gland.

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The hypothalamus regulates autonomic processes through control of the pituitary gland. The pituitary gland is known as the master gland because the pituitary gland controls most of the other glands in the human body.

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Pathologies of the limbic system can create emotional disturbances and anxiety disorders as well as other related issues. 409

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Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

➤ The Spinal Cord Within the vertebral column and beneath the brainstem is the spinal cord (Figure 12–15). The spinal cord is an elongated tubular piece of tissue made of gray and white matter tracts. The spinal cord is located beneath the medulla of the brainstem and terminates inferiorly at the level of the lumbar vertebrae: n

Most individuals inherently grasp that the spinal cord plays a large role in connecting your brain to your body. Specifically, the spinal cord houses major afferent/sensory and efferent/motor neural pathways that are responsible for the transmission of impulses between the brain and the peripheral nervous system.

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Like the brainstem, the spinal cord is also responsible for the generation of some basic reflexes that assist in survival. These are known as spinal reflexes. The most easily understood spinal reflex is the pain withdrawal reflex. Everyone at some point has burned their hand in the kitchen or on a curling iron. In response to this incoming sensation of the hand burning reaching the spinal cord, the spinal cord initiates a simple motor plan that contracts the muscles to jerk the burning hand away to best preserve the hand by minimizing the burning. It is usually while pulling the hand away or after the hand is pulled away that the person with the hand that has just been burned senses the painful stimuli. In this example, the person’s hand would be far more severely burned if that person had no pain withdrawal reflex and, as a result, had to wait until the painful afferent/sensory stimuli of hand burning was transmitted all the way to the cerebral cortex to be processed before becoming aware of the hand burning and then had to decide to act and how to respond to the burning sensation.

FIGURE 12–15.  Spinal cord. Reproduced with permission from Anatomage.

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An interesting feature of the spinal cord is that it terminates inferiorly by essentially breaking apart into many spinal nerves. Just prior to this branching apart is a narrowing of the spinal cord that occurs in the lumbar vertebrae known as the conus medullaris.

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After the conus medullaris, the group of loose strands of spinal nerves into which the spinal cord has split is named the cauda equina (Figure 12–15), which is Latin for “horse’s tail,” due to the resemblance of the spinal nerves to the strands of hair in the tail of a horse.

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A transverse section of the spinal cord reveals a shape like a gray butterfly in the middle of the spinal cord (Figure 12–16). This is gray matter surrounded by white matter that creates this distinctive pattern. The gray matter is the point of synapse for spinal nerves’ efferent and afferent pathways. The white matter surrounding this butterfly shape is responsible for the transmission of efferent impulses received from the cerebral cortex and subcortex, to be sent through the spinal cord to the appropriate point of synapse with the spinal nerves. This white matter is also responsible for transmission of afferent impulses superiorly from afferent spinal nerves to ultimately arrive at the cerebral cortex.

➤ Blood Supply to the Brain

FIGURE 12–16.  Transverse view of spinal cord.

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The human brain uses about 20% of the oxygen the body takes in, and as there is no system for storing oxygen in the body, the supply of oxygen to the brain must be constant. Oxygen is carried by red blood cells through the arterial portion of the cardiovascular system. Any interruption in the supply of blood to the brain, as in the case of stroke or heart attack, results quickly in a severe oxygen deficit. This creates a state of hypoxia or anoxia that is likely to lead to brain damage or death. For the heart to supply blood to the brain, there are large arteries coursing superiorly from the heart into the neck and brain to feed the brain’s large and constant need for freshly oxygenated blood:

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

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From the heart, the aorta branches off from the heart and the right and left subclavian arteries branch off from the aorta. The right subclavian projects off to the right to carry oxygenated blood supply to the right side of the body, while the left subclavian branches off to the left to carry oxygenated blood to the left side of the body (Figure 12–17).

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From the right and left subclavian arteries, two arterial systems arise that supply blood through the neck to the brain: the vertebral system and the carotid system (Figure 12–17).

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The vertebral arteries supply oxygenated blood to the posterior brain: n

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The internal carotid arteries supply oxygenated blood to the medial and anterior brain: n

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Right and left vertebral arteries branch from the right and left subclavian arteries, respectively, to course posteriorly then superiorly through the transverse foramen of the cervical vertebrae. After exiting the transverse foramen superiorly, the vertebral arteries join together to form a single artery, the basilar artery (Figure 12–17), which has many lateral branches supplying blood to the cerebellum. Right and left common carotid arteries branch from the right and left, respectively, to course anteriorly and superiorly. The common carotids divide into the internal and external carotid arteries. The internal carotids course superiorly from the chest through the neck and behind your ears, at which point a person’s pulse is often checked (Figure 12–17).

At the base of the brain, the basilar artery and internal carotids join to form a roughly circular structure of blood vessels known as the circle of Willis (Figure 12–18). The circle of Willis serves the highly important function of providing a point of connection between the

FIGURE 12–17.  Blood supply to the brain.

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FIGURE 12–18.  Circle of Willis. Reproduced with permission from Anatomage.

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These communicating arteries that connect the basilar and internal carotids allow the circle of Willis to function as a safeguard against hypoxia/anoxia to the brain in the case of an occlusion (such as a clot) of one of these major arteries.

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This safeguarding function is possible due to the communication between the vertebral and carotid systems that occurs at the circle of Willis. Because of these connections, blood can be rerouted from one of these systems into the other if there is a decrease or lack of blood flow in one of the internal carotid arteries, one of the vertebral arteries, or the basilar artery. In this way, the circle of Willis functions to ensure a more consistent blood flow to the brain in the case of an occlusion of an artery below the circle, thereby providing a greater chance of avoiding hypoxia/anoxia in the brain and possible brain tissue damage and death. Due to this function, the circle of Willis is often thought of as a safety valve.

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For instance, if blood flow is reduced from the right internal carotid due to an occlusion there, blood will flow from the left internal carotid and the basilar artery and will be rerouted through the communicating arteries of circle of Willis to reach those arteries lacking bloodflow due to the occluded right internal carotid (the right anterior cerebral artery and right middle cerebral artery). In this fashion areas of the brain with blood flow usually supplied by the right internal carotid may avoid tissue death and more likely ensure survival.

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The posterior anatomy of the circle of Willis is formed when the basilar artery reaches the posterior base of the brain (Figure 12–18). At this point, the basilar artery divides into the right and left posterior cerebral arteries (Figure 12–18). The posterior cerebral arteries deliver blood to posterior and inferior portions of the brain such as the cerebellum, occipital lobes, cerebellum, and inferior temporal lobes (Seikel et al., 2010).

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The anterior anatomy of the circle of Willis is formed when the internal carotids reach the base of the brain and divide into the middle cerebral arteries and anterior cerebral arteries 413

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vertebral system and the carotid system by a system of small connecting arteries known as the communicating arteries.

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

(Figure 12–18). The middle cerebral arteries project laterally and provide oxygenated blood flow to most of the lateral medial portions of the brain. This includes posterior lateral portions of the frontal lobes including the zone of language and primary motor cortex, as well as portions of the temporal lobes and parietal lobes. The anterior cerebral arteries project anteriorly to provide oxygenated blood flow toward the medial inferior frontal lobes, medial parietal lobes, basal ganglia, and corpus callosum. n

Finally, the anterior cerebral arteries, middle cerebral arteries, and posterior cerebral arteries are connected to one another by communicating arteries (Figure 12–18). Between the right and left anterior cerebral arteries, there exists a small blood vessel connecting these two known as the anterior communicating artery (Figure 12–18). On each side of the circle of Willis, between each posterior cerebral artery and each middle cerebral artery exists the posterior communicating arteries (Figure 12–18).

➤ The Peripheral Nervous System The peripheral nervous system (PNS) is composed of bundles of neurons known as nerves that course between the CNS and the body. The nerves of the PNS provide efferent communication from the CNS to the muscles and glands of the body as well as afferent communication from sensory receptors in the body to the CNS. In this way, the PNS connects the brain to the environment through afferent/sensory flow of information from sensory receptors, which is how humans perceive their environment. The PNS then allows the brain to respond to the environment by transmitting the efferent/motor flow of body commands from the CNS out to the muscles, organs, and glands of the body to move the body and regulate the body’s metabolism: n

The PNS is divided into two primary divisions: the spinal nerves and the cranial nerves.

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The cranial nerves are that portion of the PNS associated with the head and neck and synapse with the CNS at the brain and brainstem. The spinal nerves are that portion of the PNS that synapse with the CNS at the spinal cord.

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The 12 paired cranial nerves are directly associated with structures of the face and neck associated with speech, mastication, and deglutition and are, in this way, essential to the speechlanguage pathologist. The cranial nerves are covered thoroughly in Chapter 1.

The Spinal Nerves Whereas the cranial nerves are involved in control of the structures of the face and neck, the spinal nerves are associated with control of the rest of the body: n

There are 31 paired spinal nerves in the body that synapse with the spinal cord at the gray matter within the spinal cord. The spinal nerves then course out from between the intervertebral foramina of the vertebral column (Figure 12–19) to provide efferent and afferent innervation to structures of the body.

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Although speech-language pathologists spend large amounts of time considering the structure, function, and pathology of the cranial nerves, we rarely get involved in the spinal nerves, as movement of the extremities is more in the realm of physical therapy and occupational therapy. An exception to this pattern is the phrenic nerve (Figure 12–20).

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phrenic nerve (Figure 12–20) is the spinal nerve that originates in the cervical area of the spinal cord and is the sole provider of efferent signal to the diaphragm.

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As covered previously, the diaphragm is a primary muscle of respiration and is specifically the primary muscle of inspiration. Damage to this nerve can create deficits in the realm of inspiration. Speech-language pathologists spend a great deal of time working with individuals with respiratory deficits because of their lack of ability to produce phonation.

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FIGURE 12–19.  Spinal nerve coursing out between two vertebrae. Reproduced with permission from Anatomage.

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

FIGURE 12–20.  Diaphragm and phrenic nerve. Reproduced with permission from Anatomage.

➤ Chapter Summary Two important landmarks for understanding the anatomy of the cerebrum are the central sulcus that runs coronally across the medial portion of the cerebrum and the lateral sulcus that courses from the anterior, inferior, of each cerebral hemisphere and runs superiorly and posteriorly past the base of the central sulcus. The central sulci create the point of division between the frontal lobes and parietal lobes in each cerebral hemisphere. As the lateral sulci courses along the side of each cerebral hemisphere, it divides the base of each frontal lobe and parietal lobe from each temporal lobe. The anterior-most lobes of the cerebrum are the frontal lobes. Broca area is in the inferior posterior left frontal lobe and is the primary area for expressive language. The anteriormost portion of the paired frontal lobes is known as the prefrontal cortex and is responsible for higher level cognitive skills, executive functioning, initiation of movement, and inhibition of inappropriate social impulses. The posterior-most gyrus of the frontal lobes is the primary motor cortex that issues plans for volitional movement to be transmitted to the body for execution. A visual representation of the amount of cortex within the primary motor cortex devoted to the control of each body part is the motor homunculus. Posterior to the frontal lobes are the parietal lobes that are responsible for receiving and processing signals of somatosensation. The number of senses categorized as somatosensation arise in sensory receptors in the muscles, joints, and skin which generate afferent signals. The anterior-most gyrus of the parietal lobes is the primary sensory cortex, which receives and begins processing the somatosensation from the body. A visual representation of the amount of cortex

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within the primary sensory cortex devoted to the reception and processing of somatosensation from each body part is the sensory homunculus. The temporal lobes are located beneath the frontal and parietal lobes. The temporal lobes play important roles in the reception and processing of impulses of audition and also play a primary role in the creation of memory due to the hippocampi. The hippocampi function to turn short-term memory into long-term memory for storage that can be later retrieved and not simply discarded and forgotten. The presenting symptom of memory loss associated with Alzheimer disease is due to degeneration of the hippocampi. The temporal lobes also house the primary auditory cortex, left and right, which in the left temporal lobe receives auditory signals of speech sounds and transmits those signals posteriorly to be processed in Wernicke area, allowing for the comprehension of the speech of others. The posterior-most lobes of the cerebrum are the occipital lobes that house areas responsible for visual processing. The most posterior portion of the occipital lobes is the primary visual cortex that receives visual afferent information. Anterior to the primary visual cortex is the visual association cortex that is responsible for processing and interpreting the afferent information received at the primary visual cortex. A lesion or damage to the primary visual cortex results in a state of blindness referred to as cortical blindness. A bilateral lesion to the visual association cortex creates an inability to make sense of what is being visually perceived, known as visual agnosia. The brainstem is responsible for basic autonomic life-giving functions and is divided into three primary sections. From superior to inferior, these are the midbrain, pons, and medulla. The brainstem connects the spinal cord to the rest of the superior CNS. The brainstem houses somatosensory and efferent pathways coursing between the cerebrum and the body. The midbrain houses the substantia nigra that produces the neurotransmitter dopamine. Beneath the midbrain, the pons is the point of connection between the cerebellum and rest of the CNS. Beneath the pons is the medulla that houses the respiratory center, the swallowing central pattern generator, and is the point of pyramidal decussation that is the crossing of certain motor neuron pathways from one side of the body to the other. In this way, pyramidal decussation creates contralateral innervation of the body. A unilateral (one-sided) spastic weakness of the body is known as hemiparesis, whereas a full unilateral spastic paralysis is hemiplegia. Across the midbrain, pons, and medulla exists a number of nuclei that are the reticular activating system. The reticular activating system includes important structures that together work to regulate the level of wakefulness or arousal. The brainstem is also responsible for the generation of what are known as brainstem reflexes. A reflex is a simple motor response generated by the brainstem or possibly spinal cord automatically that allows a person to respond quickly to changes in their environment and thereby assist in ensuring survival. Some examples of reflexes generated at the brainstem are the gag reflex and vestibulo-ocular reflex. The cerebellum hangs off the back of the brainstem and functions as an error control device, functions to monitor volitional motor plans, and ensures that the body is appropriately executing those movements and that intended movements will achieve the desired result. The cerebellum is divided into the anterior lobe, posterior lobe, and flocculonodular lobe. These lobes are further divided into lateral cerebellar hemispheres, the left and right cerebellar hemispheres. The paired lateral cerebellar hemispheres are connected to one another at midline by a structure of gray matter

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known as the vermis. The cerebellum has three paired points of the connection with the pons known as the peduncles. These are known as the superior, middle, and inferior peduncles. The thalamus is an olive-shaped structure resting on top of the brainstem. All afferent/ sensory pathways, except for the olfactory pathway, coalesce into the thalamus as they course superiorly through the CNS. Due to this function, the thalamus is known as a relay station for afferent/sensory information. The primary function of the basal ganglia is appropriate movement of the body via the facilitation of desired voluntary movement and the inhibition of involuntary movement. However, the basal ganglia are also known to play roles in new motor learning, executive functioning, and behavior. The four major subcortical structures of the basal ganglia are the putamen, globus pallidus, subthalamic nucleus, and substantia nigra. Degeneration or damage to different structures or pathways within the basal ganglia can create a variety of movement disorders involving the lack of initiation of movement, loss of new motor learning, decreased voluntary movement, and increased involuntary movement. The limbic system is a set of subcortical structures generally located above the brainstem on each side of both lobes of the thalamus that are involved in regulating emotion, behaviors such as feeding and mating, motivation, and emotional learning. Major structures of the limbic system include the hypothalamus, amygdala, and mamillary bodies. The amygdala plays a role in the generation of negative emotions such as aggression, fear, anger, anxiety, emotional memory, and fear conditioning. The mammillary bodies are small bodies of nuclei in front of the thalamus that share connections with the hippocampus and are involved in spatial and episodic memory. The primary role of the hypothalamus is to regulate autonomic functions such as heart rate, blood pressure, urination and defecation, hunger, thirst, and sexual arousal. Pathologies of the limbic system can create emotional disturbances and anxiety disorders as well as other related issues. The spinal cord is an elongated tubular piece of tissue made of gray and white matter tracts housed within the vertebral column. The spinal cord houses major afferent/sensory and efferent/ motor neural pathways that are responsible for the transmission of impulses between the brain and the peripheral nervous system. The spinal cord is also responsible for the generation of some spinal reflexes that assist in survival. The brain needs a large and steady supply of freshly oxygenated blood to be pumped from the heart for survival. Any interruption in the supply of blood to the brain as in the case of stroke or heart attack results quickly in a severe oxygen deficit. The internal carotids are the supply of blood to the medial and anterior brain, while the vertebral/basilar arteries supply oxygenated blood to the posterior brain. At the base of the brain, the basilar artery and internal carotids join to form a roughly circular structure of blood vessels known as the circle of Willis. The circle of Willis serves the highly important function of providing a point of connection between the vertebral system and the carotid system by a system of small connecting arteries known as the communicating arteries. The peripheral nervous system (PNS) is composed of bundles of neurons known as nerves that course between the CNS and the body. The nerves of the PNS provide efferent communication from the CNS to the muscles and glands of the body as well as afferent communication from sensory receptors in the body to the CNS. The PNS is divided into the spinal nerves and the cranial nerves. The 12 cranial nerves are that portion of the PNS associated with the head and neck and synapse with the CNS at the brain and brainstem. The spinal nerves are that portion of the PNS that synapse with the CNS at the spinal cord. The phrenic nerve is the spinal nerve that originates in the cervical area of the spinal cord and is the sole provider of efferent signal to the diaphragm. The diaphragm is the primary muscle of respiration and is responsible for inspiration.

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➤ References Lanciego, J., Luquin, N., & Obeso, J. (2012). Functional neuroanatomy of the basal ganglia. Cold Spring Harbor Perspectives in Medicine, 2(12). Lund, J. P., & Kolta, A. (2006). Generation of the central masticatory pattern and its modification by sensory feedback. Dysphagia, 21(3), 167–174. Morquette, P., Lavoie, R., Fhima, M.-D., Lamoureux, X., Verdier, D., & Kolta, A. (2012). Generation of the masticatory central pattern and its modulation by sensory feedback. Progress in Neurobiology, 96(3), 340–355. Parkinson, J. (2002). An essay on the shaking palsy. 1817. Journal of Neuropsychiatry and Clinical Neuroscience (Neuropsychiatry Classics), 14(2), 223– 236. https://doi.org/10.1176/jnp.14.2.223 (Original work published 1817) Scoville, W. B., & Milner, B. (1957). Loss of recent memory after bilateral hippocampal lesions. Journal of Neurology, Neurosurgery, and Psychiatry, 20(11), 11–21. Seikel, J., King, D., & Drumright, D. (2010). Anatomy and physiology for speech, language, and hearing (4th ed.). Delmar Cengage. Yokeoka, Y., Takada, N., Inoue, A., Ibuchi, Y., Kumagai, T., Sugai, T., . . . Ueda, K. (2004). Acute Korsakoff syndrome following mammillothalamic tract infarction. American Journal of Neuroradiology, 25, 964–968.

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Balliene, B., Mauricio, D., & Okihide, H. (2007). The role of the dorsal striatum in reward and decision making. Journal of Neuroscience, 27(31), 8161–8165. Bhatnagar, S. (2008). Neuroscience for the study of communicative disorders. Wolters Kluwer/Lippincott Williams & Wilkins. Carey, B. (2008). H.M., an unforgettable amnesiac, dies at 82. New York Times. Retrieved from http://www.nytimes.com/2008/12/05/us/05hm​ .html?pagewanted=al&_rmoc.semityn.www Corkin, S. (2002). What’s new with the patient H.M.? Nature Reviews: Neuroscience, 3, 153–160. Dillingham, C., Frizzata, A., Nelson, A., & Vann, S. (2015). How do mammillary body inputs contribute to anterior thalamic function? Neuroscience & Biobehavioral Reviews, 54, 108–119. Duffy, J. (2005). Motor speech disorders: Substrates, differential diagnosis, and management (2nd ed.). Mosby. Gold, J., & Squire, L. (2006). The anatomy of amnesia: Neurohistological analysis of three new cases. Learning and Memory, 13, 699–710. Jean, A. (2001). Brain stem control of swallowing neuronal network and cellular mechanisms. Physiological Reviews, 81(2). Kril, J., & Harper, C. (2012). Neuroanatomy and neuropathology associated with Korsakoff ’s syndrome. Neuropsychological Review, 22, 72–88.

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Glossary

Abdominal aponeurosis:  a broad, sheetlike tendon that covers the anterior abdominal wall. Abdominal esophagus:  the inferior third of the esophagus that passes through the abdomen and is composed of smooth muscle. Abdominal fixation:  the muscles and tissues of the abdominal wall are tightened and secured to provide additional support to the abdominal organs. Absent pharyngeal swallow:  when the bolus enters the pharynx and stays there with no initiation of the pharyngeal swallow for 10 s or more. Accessory muscles of expiration:  a group of muscles that facilitate expiration when the demand for oxygen is increased or when there is resistance to the outflow of air. Accessory muscles of inspiration:  a group of muscles that facilitate inspiration when there is an increased demand for oxygen or when there is resistance to the inflow of air. Accessory muscles of inspiration of the back:  any muscle that has attachments at the vertebral column and courses inferiorly to attach to the rib cage and can function to elevate the rib cage upon contraction to assist in forced inspiration. Accessory muscles of inspiration of the chest:  the muscles that have medial attachments to the rib cage and distal attachments to the shoulder that can function to expand the rib cage anteriorly and superiorly to assist in forced inspiration. Accessory muscles of inspiration of the neck:  any muscle that has an attachment at the neck and courses inferiorly to attach to the rib cage and can function to pull the rib cage superiorly, thereby assisting forced inspiration. Acetabulum:  the large socket in the ischium into which the head of the femur inserts and articulates. Acoustic energy:  the sound pressure waves that vibrate the tympanic membrane. Acoustic parameters:  the measurable physical characteristics of sound waves, including frequency, amplitude, duration, and pitch. Acoustic reflex:  an involuntary reflex that occurs when the tensor tympani and stapedius muscles contract in response to loud sounds. Acoustic trauma:  also called noise-induced hearing loss; damage to the ear caused by exposure to high levels of sound at one point in time or constant exposure to moderately loud sounds over time. Acquired:  something that has been gained or developed over time. Acromion process:  the most superior and lateral-most portion of the scapula that projects above the glenoid fossa and is the point of articulation between the scapula and clavicle. Action potential:  an electrochemical impulse passed from one neuron to another. Adductors:  the muscles that bring the vocal folds together to produce phonation or speech. Aditus:  the entrance to the antrum located in the posterior wall of the middle ear and bordered by the stapes bone and the incus bone. Admittance:  the ease with which energy flows through the system. Aerodynamic:  the study of the motion of air, particularly in relation to objects moving through it. Aerodynamic parameters:  the measures of the air pressure and flow in the respiratory and phonatory systems; are important in the production of speech. 421

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Afferent pathway:  the neural pathway that carries sensory information from sensory receptors or peripheral tissues to the central nervous system. Air conduction:  the process by which sound waves travel through the air and enter the ear canal, causing the tympanic membrane to vibrate. Airflow:  how much air escapes through the vocal folds. Alternating current (AC):  an electrical current that intermittently switches directions. Alveolar air:  the air that is found in the small sacs (alveoli) within the lungs where gas exchange takes place. Alveolar ducts:  the smallest of air passages in the lungs that connect the respiratory bronchioles to the alveolar sacs. Alveolar pressure:  the air pressure inside the alveoli of the lungs. Alveolar process:  a portion of the mandible that houses the dental alveoli for the upper dental arch. Alveolar sacs:  the chambers within which groups of individual alveoli are formed. Alveoli:  the tiny, air-filled sacs located in the lungs where gas exchange occurs. Amphiarthrodial joints:  the joints where the bones are connected to cartilage and allow limited movement. Amplitude:  the degree or magnitude of displacement of a particle from its mean position or resting state; the maximum displacement of a wave from equilibrium that has the perceptual correlate of loudness. Amplitude of vibration:  the degree of lateral excursion of the vocal folds from the midpoint. Ampulla (plural:  ampullae):  a vestibule in the inner ear located within the semicircular canals that contains the crista ampularis. Amygdala:  a small, almond-shaped structure located deep within the temporal lobes of the brain that plays a role in the generation of negative emotions such as aggression, fear, anger, and anxiety. Amylase:  an enzyme that is the active component of saliva. Anatomical variation:  the nonpathological structural anomalies that are different from normal. Anatomy:  the study of the structure of organisms and their parts. Anencephaly:  a severe and rare birth defect in which a baby fails to develop the cerebrum. Angle of the mandible:  the point at which the body of the mandible meets the rami. Angle of the rib:  the location on the rib where the shaft changes direction from a lateral course to an anterior course. Annular ligament:  a ligament located in the middle ear that connects the footplate of the stapes bone to the oval window. Anotia:  missing pinna. Anoxia:  a complete lack of oxygen supply to either the entire body or a specific body part, including but not limited to the brain, heart, and other organs. Anterior cerebral arteries:  paired arteries that originate from the internal carotid arteries and project anteriorly to provide oxygenated blood flow toward the medial inferior frontal lobes, medial parietal lobes, basal ganglia, and corpus callosum. Anterior communicating artery:  a small blood vessel connecting the right and left anterior cerebral arteries. Anterior gap:  a gap near the anterior commissure of the vocal folds (toward the vocal folds’ attachment with the thyroid cartilage). Anterior ligament:  a small ligament located in the middle ear that connects the neck of the malleus to the anterior wall of the middle ear. Anterior scalenes:  the anterior-most pair of scalene muscles that can function to elevate the first rib for inspiration. 422

Glossary

Anterior semicircular canal:  also called the superior semicircular canal; oriented vertically and perpendicularly to the temporal bone’s long axis. Anterior wall of the eustachian tube:  also called the carotid wall; contains the opening of the eustachian tube. Antitragus:  the inferior margin of the concha opposite to the tragus. Antrum:  a small, air-filled space located in the mastoid bone; helps to regulate pressure within the ear, promoting efficient transmission of sound. Aortic hiatus:  the opening through which the abdominal aorta passes on its way from the heart into the abdomen to supply oxygenated blood to the lower half of the body. Aperiodic:  the time it takes to complete each cycle is inconsistent. Apex of the cochlea:  the tapered end of the cochlea. Aponeurosis:  a strong, flat, sheetlike tendon. Appendicular skeleton:  includes the limbs as well as the skeletal structures in the limbs, the pelvic girdles, and the pectoral girdles (also known as the shoulder girdles) — these form the complete skeleton. Applied anatomy:  the application mainly concerned with the diagnosis and treatment of various conditions as well as the application of anatomical knowledge to specific fields (e.g., surgery). Approximal surfaces:  the surfaces of side-by-side teeth that are in contact with one another. Arachnoid mater:  the middle meningeal layer contains a high number of blood vessels and supplies blood to the surface of the brain. Arbor vitae:  a treelike pattern in the white matter projections within the cerebellum. Arcuate fasciculus:  a white matter pathway that connects Broca and Wernicke areas. Area advantage:  where the sound intensity is increased as sound waves pass through an expanding area. Articular capsule:  a structure that surrounds and holds the synovial joints. Articulation:  the act of using the structures of the vocal tract to shape phonemes for speech production. Articulatory system:  a system of organs and structures that are involved in the production of speech sounds. Aryepiglottic folds:  the paired structures that form the upper portion of the quadrangular membrane. Arytenoid cartilages:  a pair of small, pyramid-shaped cartilages located in the larynx that sit on top of the cricoid cartilage, which forms the base. Arytenoids:  the paired hyaline cartilages; important for speech production because they are attached to the vocal folds and allow for movement of the folds. Aspiration:  when foreign material passes into the airway below the true vocal folds. Astrocytes:  the neuroglial cells that provide structural support for neurons in the intercellular space between neurons in the central nervous system and function to maintain homeostasis in the central nervous system. Astrogliosis:  the protective process of astrocyte proliferation around an injury in the brain to contain inflammation. Atlas:  the first cervical vertebra. Atresia:  when the external auditory meatus does not form appropriately during development. Audiogram:  a graphical representation of the threshold for each frequency in each ear. Audition:  the sensation of hearing. Auditory, acoustic, vestibulocochlear, or auditory vestibular nerve:  the eighth cranial nerve; responsible for transmitting sensory information related to hearing and balance from the inner ear to the brain. Auditory brainstem response (ABR):  a diagnostic tool for sensorineural hearing loss that measures the electrical activity of the auditory nerve and brainstem in response to sound stimuli. Auditory cortex:  the region of the brain responsible for processing sound information. 423

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Auditory-evoked potentials:  electrical responses that are recorded from the scalp in response to sound stimuli. Auricle:  also known as the pinna; a cartilaginous structure designed to collect sound waves and direct them into the ear canal. Auricular cartilage:  the flexible, elastic cartilage that forms the shape and structure of the auricle. Auricular (Darwin) tubercle:  a thickened protuberance frequently found on the superior and posterior portion of the helix. Auricular orifice:  also called the external orifice; the inner end of the first one third of the ear canal and where the diameter of the external auditory meatus is the largest. Autophonia:  a medical condition characterized by the perception of abnormally loud sounds originating from one’s own body, particularly the head or ears. Axial skeleton:  comprises the bones of the trunk and the head. Axis:  the second cervical vertebra. Axon:  a type of nerve fiber that sends action potential signals to the adjoining neuron at junctions. Axons transmit electrical impulses, or action potentials, over long distances to allow communication between different parts of the nervous system. Axon terminal:  the specialized end of the axon at which an axon synapses with the dendrites of other neurons. Basal end:  the part of the inner ear closest to the middle ear; the site where the vibrations of the stapes bone are transmitted into the fluid-filled cochlea. Basal ganglia:  a group of interconnected nuclei located deep within the brain primarily responsible for appropriate movement of the body via the facilitation of desired voluntary movement and the inhibition of involuntary movement; also important for new motor learning, executive functioning, and behavior. Base:  the largest part of the cochlea. Basement membrane:  a thin, specialized layer of extracellular matrix that separates and supports the epithelial and endothelial cells from the underlying connective tissue. Basilar artery:  a major blood vessel that arises from the paired vertebral arteries at the level of the medulla oblongata in the brainstem, has many lateral branches supplying blood flow to the cerebellum, and courses superiorly to the circle of Willis. Basilar membrane:  also called the cochlear partition; a thin, fibrous membrane in the cochlea that separates the scala media from the scala tympani. Bell palsy:  a condition that causes sudden, temporary weakness or paralysis of the muscles on one side of the face. Bernoulli effect:  as air passes through a point of constriction (the glottis), the velocity of airflow increases, resulting in a decrease in pressure. Bicuspids:  the premolars; used for grinding food once a portion of food suitable for mastication is in the mouth. Bilateral innervation:  the innervation of a structure or organ by nerves that originate from both sides of the body. Biological functions of the larynx:  breathing, abdominal fixation, protection during the swallowing reflex, throat clearing, and coughing. Biological system:  a network or a group of two or more organs that combine to function together. Biology:  the study of living organisms and their processes. Blood–brain barrier:  a protective layer of cells that keep such unwanted or dangerous molecules such as poisons or pathogens from moving into the brain from the circulatory system. 424

Glossary

Blood oxygen level:  oxygen saturation; the amount of oxygen-saturated hemoglobin compared to the total volume of hemoglobin in the body; the amount of oxygen in the bloodstream. Body of hyoid:  the U-shaped bone located in the neck, just above the thyroid cartilage and below the mandible. Body of the mandible:  the curved portion of the mandible creating the framework for the lower dental arch. Body-cover theory:  the structure of the vocal folds plays a role in their vibration. Bolus:  a ready-to-swallow mass of food or liquid. Bone:  a part of the vertebrate skeleton and is the hardest structure of the body. Bone conduction:  the transmission of sound waves through the bones of the skull. Bony thorax:  a rigid bone of the thorax that provides structure to the thorax and support to soft tissues of the thorax. Boyle’s law:  states that given a constant temperature, if the volume of a container is decreased, air pressure within that container increases, whereas if the volume of a container is increased, air pressure within the container decreases. Brainstem:  the inferior portion of the brain between the cerebrum and the spinal cord; responsible for many autonomic, life-giving functions. Breathy vocal attack:  when airflow begins prior to adducting the vocal folds. Broca area:  a region of the brain located in the inferior posterior left frontal lobe that is highly responsible for expressive language. Bronchial tree:  the branching of the respiratory passages into sequentially smaller and smaller passages between the primary bronchi and the alveoli. Brownian motion:  a random, high-speed, and constant motion in which molecules in a gas or liquid are constantly colliding with each other. Buccal cavity:  the space between the lateral dental arches, the posterior teeth, and the flesh of the cheeks. Buccal surface:  the surface of the teeth that contacts the inside of the cheeks. Buccinator:  the primary muscle of the cheeks responsible for compression of the cheeks against the teeth to keep food from falling into the buccal cavities. Calcium ions:  play a crucial role in a wide range of physiological processes in the human body, including muscle contraction, nerve function, blood clotting, and bone formation. Carbon dioxide poisoning/hypercapnia: a destructive and poisonous overabundance of carbon dioxide in the blood. Cardiac (semi-striated) muscles:  contract involuntarily, are found in the heart, and may be triggered by endocrine or peripheral plexus activation or because of messages received by the central nervous system. Carhart notch:  a characteristic dip in the bone conduction audiogram at around 2000 Hz. Carina:  where the trachea branches into the left and right primary bronchi. Cartilage:  smooth elastic tissue. Castrato:  a person who only has a high-sounding voice. Cauda equina:  the loose strands of spinal nerves into which the spinal cord terminates. Cavum conchae:  the lower portion of the concha. Cell structures:  the basic units of organisms and the building blocks of life. Cells of Claudius and Boettcher:  the columnar and cuboidal cells that make up the stria vascularis found in the organ of Corti. Cellular respiration:  a cell’s use of oxygen for metabolic purposes in the production of energy to power the cells of the body and the by-product of carbon dioxide from this process. 425

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Cementum:  the substance that coats the root of a tooth and holds the tooth in place. Central nervous system:  the portion of the nervous system made up of the brain and the spinal cord. Central sulcus:  a prominent sulcus that divides the frontal lobes from the parietal lobes. Central tendon:  the heart-shaped aponeurosis (sheetlike tendon) centered in the diaphragm. Cerebellum:  a structure of the brain that hangs posteriorly off the brainstem beneath the posterior cerebrum and plays an important role in coordinating and controlling voluntary movement, balance, and posture. Cerebral cortex:  the most superficial layer of the cerebrum where the highest-level cognition and sensory/motor processing occurs. Cerebral meninges:  three layers of nutritive and protective tissue that are located between the inner surface of the skull and the surface of the brain and spinal cord. Cerebrospinal fluid:  the fluid present in the space between the pia mater and the arachnoid mater in the central nervous system. Cerebrum:  the most superior section of the brain; a large, gray, and rounded portion of the brain with a wrinkled-appearing surface. Cerumen:  commonly known as earwax; a yellowish, waxy substance that is created in the first one third of the external auditory meatus. Cervical esophagus:  the most superior section of the esophagus that is composed of striated muscle. Cervical vertebrae:  the superior-most seven vertebrae of the vertebral column; located between the thorax and skull. Characteristic frequency:  the frequency that requires the minimum amount of intensity to cause the nerve fiber to fire. Cheeks:  constitute the lateral walls of the oral cavity and are appropriate for maintaining normal oral resonance. Chondral portion of the internal intercostals:  the anterior-most section of the internal intercostals that assists the external intercostals during forced inspiration. Chorda tympani:  a branch of the facial nerve that travels within the posterior wall of the ear. Choroid plexus:  the tissue located in the lateral ventricles that produces most of the cerebrospinal fluid in the ventricular system. Chronic middle ear disease:  disrupts the incudostapedial joint and damages the ossicles, resulting in a moderate conductive hearing loss. Cilia:  microscopic, hairlike structures that protect the ear canal. Circle of Willis:  a roughly circular structure of blood vessels located at the base of the brain that connects the carotid and vertebral artery systems. Circulatory/cardiovascular system:  a network of vessels and organs that circulate blood and lymph throughout the body. It includes the blood vessels, blood, and heart. Circumvallate papillae:  small, bumplike structures that give the tongue a rough texture and house taste buds and temperature receptors. Coccygeal vertebrae:  the inferior-most vertebrae that constitute the coccyx. Coccyx: the fused coccygeal vertebrae that constitute the tailbone. Cochlea:  also called the osseous cochlear labyrinth; a spiral-shaped, bony structure located in the inner ear containing hair cells. Cochlear aqueduct:  a small opening near the round window between the scala tympani and the cranial cavity. Cochlear branch:  also known as the auditory branch; a branch of the vestibulocochlear nerve (cranial nerve VIII) that is responsible for transmitting auditory information from the cochlea of the inner ear to the brainstem. 426

Glossary

Cochlear microphonics (CMs):  the electrical signals that are generated by the hair cells in the cochlea of the inner ear in response to sound waves. Cochlear nucleus:  a group of nuclei located in the brainstem that receive input from the cochlea. Cochleariform process:  a curved bone separating the tensor tympani from the orifice of the eustachian tube. Coding intensity:  the way in which the auditory system represents the intensity or loudness of sound. Commissure of the lips:  where the vermilion border of the lower lip meets the vermilion border of the upper lip. Common carotid arteries:  large blood vessels that course from the heart to supply oxygenated blood to the head and brain. Comparative anatomy:  the study of similarities and differences in the structures of all living organisms. Compressions:  the areas of high pressure in a sound wave. Concha:  the hollow, bowl-shaped depression located in the central part of the external ear. Conductive hearing loss:  when sound is unable to be conducted through the outer and/or middle ear. Condylar head:  the rounded, protruding end of the condylar process of the mandible that articulates with the skull at the temporomandibular joint. Condylar neck:  the narrow, cylindrical portion of the condylar process that connects the condylar head to the ramus. Cone of light:  a triangular reflection of otoscope light radiating from the umbo seen on the tympanic membrane. Congenital:  a condition or trait that is present at birth or that arises during fetal development. Congenital abnormalities:  also known as birth defects; the physical or structural abnormalities that are present at birth. They can be caused by genetic or environmental factors or a combination of both. Connective tissue proper:  includes loose and dense connective tissue. Contralateral innervation:  the neural connections between one side of the brain and the opposite side of the body. Conus elasticus:  a yellow, elastic funnel-like cavity that resides below the vocal folds; integral to the makeup of the vibrating part of the vocal folds. Conus medullaris:  the tapered lower end of the spinal cord that is distal to the cauda equina. Coracoid process:  a bony projection of the scapula that is the point of attachment between the arm and pectoral muscles of the chest. Corniculate cartilage:  a small conical structure at the top of each arytenoid cartilage. Coronoid process:  a triangular bony protrusion located superiorly on the ramus of the mandible and anterior to the condylar process that provides a point of attachment of muscles of mastication. Corpus/body:  the central part of an organ or structure. Corpus callosum:  a bundle of nerve fibers that is located in the center of the brain and connects the right and left hemispheres of the cerebral cortex. Corrugator:  the muscle responsible for wrinkling the forehead. Cortical blindness:  blindness that is the result of a lesion or damage to the primary visual cortex. Cortilymph:  a fluid in the tunnel of Corti. Costal groove:  a longitudinal groove on the inferior surface of each rib. Costotransverse joints:  the points of articulation between ribs at the tubercle of the rib and the transverse processes of the thoracic vertebrae. Costovertebral joints:  the points of articulation between the ribs and corpus of the thoracic vertebrae. Countertenor:  a type of male singer who sings in a high voice but can also produce low notes as well. Cranial nerve X:  the vagus nerve; it innervates the larynx bilaterally. Cranial nerves:  a set of 12 pairs of nerves that emerge from the brain and are responsible for controlling a variety of functions in the head and neck region. 427

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Cricoid cartilage:  a ring-shaped cartilage structure located at the base of the larynx in the neck. Cricothyroid joint:  a synovial joint located between the cricoid cartilage and the thyroid cartilage in the larynx. Cricothyroid ligament:  a strong, fibrous band that connects the thyroid cartilage and cricoid cartilage in the larynx. Cricothyroid muscle:  a paired muscle located in the larynx that connects the cricoid cartilage to the thyroid cartilage. Cricotracheal membrane:  connects the lower portion of the cricoid cartilage with the first ring of the trachea. Crista ampullaris:  the sensory organ for movement located within the ampulla in the inner ear. Crossed fibers:  nerve fibers that cross over to the opposite side of the body before reaching their final destination in the brain or spinal cord. Crown:  the portion of the tooth projecting above the gingiva. Crura antihelicis:  also called the helical crura; two curved structures in the ear that form the superior portion of the antihelix. Cuneiform cartilages:  the wedge-shaped elastic cartilages that are located above and behind the corniculate cartilages and are covered by the aryepiglottic folds. Cupid’s bow:  where the philtral pillars meet the upper lip at two peaks in the upper lip that form a curvature of the lip. Cupola:  also called the cupula; a gelatinous structure located in the ampulla of each of the three semicircular canals in the inner ear. Curved membrane buckling:  when the tympanic membrane vibrates as a result of sound energy so that one arm of the malleus does not move as much as the tympanic membrane. Cuspids:  the teeth used for gripping and tearing food. Cuticular layer:  the thin layer of skin that covers the outer surface of the tympanic membrane. Cycle of respiration:  one inspiration and one expiration. Cymba conchae:  the upper part of the concha in the external ear. Cytology:  the study of cell structures and functions. Dead air:  the air that exists in the passageways of the lungs that are not directly involved in gas exchange. Decibel (dB):  the unit used to measure intensity of a sound wave. Deciduous teeth:  the first set of teeth that develop; colloquially known as one’s baby teeth, or milk teeth. Deiters cells:  supporting cells embedded in the basilar membrane. Delayed pharyngeal swallow:  when the pharyngeal swallow is cued after the bolus passes into the pharynx but prior to 10 s. Dendrites:  projections that extend from the soma and synapse with axons of other neurons and receive information from the axons of these other neurons. Dense connective tissue:  includes dense regular (composed of closely packed collagen fibers that provide stability and strength to structures such as ligaments, tendons, and fascia) and dense irregular tissue (has collagen fibers arranged in a more random pattern, giving it greater resistance and flexibility to stress in multiple directions). Dense irregular tissue:  a type of fibrous connective tissue that is present in the deep layers of the skin, digestive tract, and lymph nodes. Dense regular tissue:  a type of tissue that joins tissues in different parts of the body. Dental alveoli:  the sockets of the upper and lower dental arches from which the teeth grow and are secured. 428

Glossary

Depolarization:  a physiological process that occurs when the membrane potential of a cell becomes less negative, or more positive, than its resting potential. Depressor anguli oris:  a paired muscle that squeezes the corners of the mouth medially and inferiorly, thereby depressing the corners of the mouth. Depressor labii inferioris:  a paired muscle that insert into the lower lip and depresses the lower lip and also can retract the lower lip inferiorly and laterally. Depressors:  a division of the muscles of the face that depress the lower lip or corner of the mouth. Depressors of the velum:  a division of muscles of the velum that lower the velum. Descriptive anatomy:  the study of organ systems that work together. Developmental anatomy:  the study of how an embryo develops from a single cell to evolve into a human being. Diaphragm:  a large, dome-shaped muscle that separates the thoracic and abdominal cavities and is the primary muscle of inspiration. Diarthrodial/synovial joints:  the most common type of joint in the body. They are highly mobile joints that allow for a wide range of movement in different directions. Diffusion:  the process by which oxygen and carbon dioxide move passively through cell walls and across alveolar and capillary walls from areas of high concentration to areas of low concentration. Digastric:  a paired muscle located in the neck region of the human body. It elevates the larynx and the hyoid bone and depresses the mandible. Digestive system:  a complex system of structures and organs that work together to break down food and absorb nutrients. Diphthong:  a vowel-like consonant that is produced with an open vocal tract and is characterized by a transition from one tongue position to another that produces transition from one vowel sound to another within a single syllable. Direct current (DC):  an electrical current that flows in one direction. Discharge rate:  the rate that the nerve fiber fires as the result of the increase with the intensity of the stimulus. Distortion product OAEs (DPOAEs):  the sounds that are elicited with two pure tone frequencies that are presented simultaneously and closely spaced at moderate intensity levels. Dorsal midbrain:  a region of the brainstem located in the upper part of the midbrain. Dorsal striatum:  a portion of the basal ganglia that is the globus pallidus, putamen, and caudate nucleus. Ductus reuniens:  a small canal that connects the cochlear duct of the inner ear to the saccule. Dura mater:  the most superficial of the cerebral meninges that is dense, fibrous, and protective in nature. Dysphagia:  any change that decreases function of mastication and deglutition outside of the range of normal to a degree of impairment. Earlobe:  the most inferior portion of the pinna composed of connective tissue. Efferent pathway:  the neural pathway that carries signals away from the central nervous system to peripheral organs or tissues. Elasticity:  a material’s ability to return to its original size and shape when a distorting force is removed. Electrocochleography (ECOG or ECochG):  a diagnostic test that examines the function of the inner ear and auditory pathway; can be performed with either invasive or noninvasive electrodes. Elevators:  a division of the muscles of the face that elevate the upper lip or corner of the mouth. Elevators of the velum:  a division of muscles of the velum that elevate the velum. Enamel:  the hard, white substance composed almost entirely of minerals that coat the crowns of the teeth. End feet:  the specialized structures of astrocytes that work to form the blood–brain barrier. 429

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Endocochlear potential (EP):  an about +80 mV voltage difference that exists between the endolymph in the scala media of the inner ear. Endocranium:  the base inner portion of the skull. Endocrine system:  a complex network of organs and glands that communicates by using hormones produced by the thyroid, parathyroid, adrenal glands, and endocrine glands — which include the pituitary glands, pineal gland, and hypothalamus. Endolymph:  a liquid found within the scala media of the inner ear that has a high concentration of potassium ions and a low concentration of sodium and calcium ions. Endolymphatic duct:  the indirect connection of the utricle and saccule. Endomysium:  a fibrous tissue that separates muscle fibers from each other. Enteric nervous system:  a complex network of nerves that controls the function of the gastrointestinal system. It is sometimes called the “second brain” because it can operate independently of the central nervous system. Epicranius:  a supplementary muscle of facial expression involved with wrinkling the forehead and raising the eyebrows. Epiglottis:  a thin, leaf-shaped cartilaginous flap located at the base of the tongue that descends to cover the opening to the larynx during a swallow to assist in preventing the aspiration or penetration of foods and liquids into the airway. Epimysium:  a layer of connective tissue that surrounds an entire skeletal muscle. Esophageal hiatus:  the opening in the diaphragm through which the esophagus passes on its course down to the stomach. Esophageal motility disorder:  when the duration and/or amplitude of esophageal peristalsis is uncoordinated, too weak, or too strong. Esophageal peristalsis:  a coordinated autonomic series of constrictions of the walls of the esophagus that propels a bolus inferiorly to be deposited in the stomach. Esophageal rings/webs:  lesions that are bands of mucosal/submucosal tissue that form points of constriction within the esophagus. Esophageal stage:  the fourth and final stage of deglutition characterized by the bolus passing through the esophagus to the stomach. Esophagitis:  an inflammation of the linings of the esophagus. Esophagus:  the collapsed muscular tube connecting the pharynx to the stomach that conducts food and liquids being swallowed from the laryngopharynx to the stomach. Ethmoid:  a complex unpaired bone deep to the maxillae that forms a boundary between the nasal cavity and the cranium. Eustachian tube:  also called the auditory tube or pharyngotympanic tube; a narrow canal that connects the middle ear to the back of the pharynx and plays an important role in equalizing the pressure between the middle ear and the outside environment. Excretory system:  responsible for the removal of waste products from the body. It includes the kidney, ureters, urethra, and bladder. Expiration:  the process of expelling carbon dioxide–rich air from inside the lungs back into the environment. Expiratory reserve volume:  the maximal amount of air that can be expired after a tidal expiration. External auditory meatus (EAM):  also called the ear canal or auditory canal; a tubelike structure that runs from the outer ear to the middle ear and is responsible for localizing, collecting, and guiding sounds into the middle ear. External branch of the superior laryngeal nerve:  one of two branches of the superior laryngeal nerve, which is a branch of the vagus nerve. 430

Glossary

External intercostals:  a group of muscles that are located between the ribs and function as important muscles of inspiration. External oblique abdominis:  the largest and most superficial of the abdominal muscles. Extratympanic (ET) electrodes:  placed outside the ear canal, but still within the external ear, to record or stimulate electrical activity in the inner ear. Extrinsic auricular ligaments:  a group of ligaments that attach the auricle to the side of the head. Extrinsic laryngeal membrane:  a thin layer of connective tissue that surrounds the larynx and attaches it to adjacent structures in the neck. Extrinsic laryngeal membranes and ligaments:  membranes and ligaments that connect the laryngeal cartilages with other structures outside the larynx. Extrinsic muscles of the larynx:  a group of muscles that are located outside of the larynx but attach to it and are responsible for moving the larynx as a whole. Extrinsic muscles of the tongue:  the muscles of the tongue that originate elsewhere and insert into the tongue and are responsible for gross movement of the tongue. False vocal folds:  the two folds of mucous membrane that are located above the true vocal folds in the larynx. Falsetto register:  when the vocal folds are thin and tense. They move to produce a higher frequency and breathier sound. Fascia:  a sheet of dense connective tissue that is mainly made up of collagen and supports and surrounds organs, muscles, and other structures within the body. Fasciculi:  the groups of muscle fibers within the skeletal muscle that are enclosed within a layer of connective tissue called perimysium. Fiberoptic endoscopic evaluation of swallow (FEES):  a form of swallowing evaluation where a fiberoptic endoscope is passed through the nasal cavity to the nasopharynx to observe the anatomy, physiology, and features of deglutition during the swallow. Fibrocartilage:  a type of cartilage that functions best as a cushion and is found in areas of the body that experience high levels of pressure such as the intervertebral discs. Filter:  the way the vocal tract modifies the sound produced by the vocal folds before it is emitted as speech or singing. Fissures:  deep grooves in the cerebrum that create major anatomical divisions of the cerebrum. Fixators:  the muscles that provide stability and help to support and stabilize the movement of other muscles during a specific activity or movement. Foramen vena cava:  the opening in the diaphragm through which the inferior vena cava passes in its course from the abdomen back into the thorax. Forced expiration:  the activation of the muscles of expiration to expire more air more quickly than would occur during a passive expiration. Forced inspiration:  employs the diaphragm as well as the accessory muscles of inspiration to increase the volume of air inspired and the speed of inspiration above which would occur during a quiet inspiration. Forced respiration:  the pattern of respiration in which additional muscular activity is used to increase the amount of air inspired and expired and to increase the rate of respiration. Frequency:  the number of vibratory cycles that occur during vocal fold vibration in a specified unit of time; commonly referred to in cycles per second (cps) and represented by the symbol Hz (hertz). Frequency coding:  the way in which the auditory system represents different frequencies of sound. Frontal bone:  a large, unpaired bone that is the forehead and is the anterior superior portion of the cranium. 431

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Frontal lobes:  the anterior-most lobes of the cerebrum responsible for executive functions, motor control, speech, language, emotions, and social behavior. Frontal processes:  a bony projection of the zygomatic bones that reach superiorly above the nasal cavity to articulate with the frontal bone superiorly and also with the nasal bones. Frontal/coronal plane:  divides the body into ventral/anterior (belly) and dorsal/posterior (back). Functional residual capacity:  the amount of air in the lungs after a passive expiration. Fundamental frequency:  the lowest frequency of a vibrating body; the primary frequency of vibration of the vocal folds. Gag reflex:  a brainstem reflex that occurs when parts of the posterior oral cavity or posterior pharyngeal wall are touched; causes contraction of the pharynx and closure of the airway to prevent aspiration and penetration. General anatomy:  the study of gross and microscopic structures including different parts of the body, its fluids, and tissues. Geniohyoid:  a small, paired muscle located in the neck region of the human body. It elevates the larynx and the hyoid bone and depresses the mandible. Genome:  the genetic material of an organism. Gingiva:  the gums of the dental arches. Gingival line:  also called the gum line; the point on the tooth where it meets the gingiva. Glenoid fossa:  the facet formed by the scapula into which the head of the humerus, the large bone of the upper arm, attaches. Glial cells:  also called neuroglia or simply glia; the nonneuronal cells that provide support and protection to neurons in the nervous system. They are the “glue ” that keeps the nervous system together. Glial scar:  the barrier created by proliferating astrocytes around an injury in the central nervous system. Glottal fry:  also called pulse register; a vocal register that is characterized by a low, rumbling, creaky sound produced by the vibration of the vocal folds at a low frequency. Glottal vocal attack:  the vocal folds are adducted prior to the initiation of airflow. Glutamate:  an amino acid that functions as a neurotransmitter in the central nervous system. Glycolytic fibers:  also known as Type II muscle fibers or fast-twitch fibers; a type of skeletal muscle fiber that contracts quickly but fatigues rapidly. They can produce a large amount of force in a short time. Goblet cells: the specialized cells found in the epithelial lining of the respiratory passages that produce and secrete mucus, helping to protect the airway from foreign particulates. Gomphosis:  a joint that is found between the root of the teeth and the socket of the mandible (jawbone). Gray matter:  the dark-colored tissue that is found in the brain, cerebellum, brainstem, and spinal cord. It is made up of capillaries, glial cells, dendrites, axons, synapses, and neuronal cell bodies. It is called “gray” because it lacks myelin. Greater horns of hyoid:  the two bony projections that extend laterally from the body of the hyoid bone. Gross anatomy:  the study of animal body parts visible to the naked eye. Ground substance:  a fluid that slows down the spread of pathogens. Gustatory system:  the sensory system of taste. Habenula perforata:  a group of perforations that provide passage for the olfactory nerves. Habitual pitch:  the frequency of vibration that is used most regularly and often by an individual. Hard palate:  the bony structure that forms the roof of the mouth and separates the oral cavity from the nasal cavity. Harmonics:  multiples of the fundamental frequency. 432

Glossary

Head of each rib:  the rounded end of the rib that articulates with the thoracic vertebrae forming the costovertebral joint. Helicotrema:  a small opening or canal that connects the scala tympani and scala vestibuli located at the apex of the cochlea. Helix:  the outermost ridge of the pinna. Hemiparesis:  a unilateral spastic weakness of the body. Hemiplegia:  a unilateral spastic paralysis of the body. Hensen cells:  column-shaped cells that support the outer hair cells and the tectorial membrane in the ear. Herpes:  an infection caused by the herpes simplex virus. Heschl gyrus:  also called the transverse temporal gyrus; found in the area of the primary auditory cortex located in the temporal lobe that receives the frequency characteristics of the signal. High-frequency sounds:  vibrate the basilar membrane at the basal end of the cochlea. High-resolution manometry:  a method of evaluating the levels of pharyngeal pressures present during deglutition. High-speed digital videoendoscopy:  a type of digital recording technique for viewing vocal fold vibration that allows sampling rates up to 2,000 to 4,000 frames per second. Hippocampi:  a pair of seahorse-shaped structures located deep within the inferior curl of the temporal lobes that function to turn short-term memory into long-term memory that can be later retrieved and not simply discarded and forgotten. Histology:  the study of tissues under a light or electron microscope. Hourglass shape:  created when there are both anterior and posterior gaps. Hyaline cartilage:  a type of cartilage that is characterized by its smooth, glassy appearance. Hydrocephalus:  a buildup of too much cerebrospinal fluid in the cerebrospinal fluid system that increases intracranial pressure. Hyoepiglottic ligament:  connects the anterior part of the epiglottis to the upper body of the hyoid. Hyoid bone:  the U-shaped bone that is part of the axial skeleton and resides in the anterior of the neck. Hyolaryngeal excursion:  occurs when the swallow reflex is triggered; the hyoid bone is drawn upward and anteriorly, resulting in the larynx moving in the same direction which helps prevent penetration or aspiration. Hypernasality:  when there is a greater than normal amount of nasal resonance in speech. Hyperpolarization:  a change in the electrical potential across the membrane of a cell, in which the potential becomes more negative than the resting potential. Hyponasality:  when there is a less than normal amount of nasal resonance in speech. Hypopharynx:  also called the laryngopharynx; the most inferior division of the pharynx. Hypothalamus:  a subcortical structure just below the thalamus with the primary role of regulating autonomic functions. Hypoxia:  a condition in which the body or a part of the body has a less than adequate supply of oxygen. Ilium:  the largest bone of the pelvic girdle; forms the upper and widest part of the hip. Illness:  a state of poor health or a condition that disrupts normal bodily functioning, including but not limited to rubella, syphilis, herpes, and meningitis. Immittance meter:  a diagnostic tool used to measure the acoustic immittance of the middle ear. Immobile articulators:  the vocal tract structures upon which the mobile articulators act for speech but which are themselves incapable of movement. Immune system:  a complex network of molecules, cells, proteins, tissues, and organs that work together to defend against disease. Impacted ear canal:  the ear canal is excessively packed with earwax or a foreign substance. 433

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Impedance:  the blockage of energy flowing through the system. Incisivus labii inferior:  a muscle that originates at the integument (skin) in the region of the mouth with fibers that run parallel to those of the transverse fibers of the orbicularis oris of the lower lip and insert into the orbicularis oris. Incisivus labii superior:  a muscle that originates at the maxilla above the canine teeth with fibers that run parallel to the transverse fibers of the orbicularis oris of the upper lip and insert laterally to the angle of the mouth. Incisors:  elongated, thin, and quadrilateral-shaped teeth with a sharp edge used primarily for cutting food. Incus:  also called the anvil; one of the three small bones in the middle ear, located between the malleus (hammer) and the stapes (stirrup). Inertia:  the tendency for an object in motion to stay in motion or an object at rest to stay at rest unless acted upon by an outside force. Inertial properties:  the tendency of an object to resist changes in motion. Inferior cerebellar peduncles:  one of three neural structures known as peduncles that connect the cerebellum to the brainstem; responsible for receiving somatosensory information concerning body position and location of the body within space. Inferior colliculus:  a structure located at the dorsal midbrain that receives information from the superior olivary complex, CN VIII, and plays a role in the localization of sound and visual orientation. Inferior nasal conchae:  the small, scroll-shaped bones that form the lateral walls of the nasal cavity. Inferior pharyngeal constrictor muscle:  also called the cricopharyngeus muscle; a circular muscle located at the lower end of the pharynx, just above the esophagus. Inferior wall:  also called the floor of the middle ear cavity or the jugular wall; divides the middle ear space and the jugular fossa. Inner ear:  also called the labyrinth; located in the petrous part of the temporal bone. Inner hair cells (IHCs):  the sensory cells located in the cochlea of the inner ear responsible for frequency coding. They convert sound vibrations into electrical signals that can be transmitted to the brain for interpretation. Innermost intercostals:  a group of muscles located in the intercostal spaces and deep to the internal and external intercostal muscles; they contract to assist in forced expiration. Insertion:  the point where a muscle, tendon, or ligament attaches. Inspiration:  the process of pulling air into the lungs. Inspiratory capacity:  the total amount of air that can be inhaled from the point of a tidal expiration. Inspiratory checking:  the slow relaxing of muscles of inspiration after an inspiration that allows the thorax to retract slowly, therefore allowing expiratory volume to be carefully controlled and utilized for speech. Inspiratory reserve volume:  the maximal amount of air that can be inspired after a tidal inspiration. Insula:  a structure within the temporal lobe that processes the temporal aspects of sounds. Integumentary system:  the organ system that consists of the nails, skin, hair, and associated glands. It protects the body from external damage and helps regulate body temperature. Intensity:  the amount of power transferred by a sound wave. Interarytenoid muscle:  made up of the transverse and oblique arytenoid muscles. Intermaxillary suture:  where the paired maxillae fuse with the opposite maxilla’s palatine process at a midline. Intermediate (fibrous) layer:  situated between the outer and inner layers of the tympanic membrane. Internal auditory meatus:  also called the internal auditory canal; a small opening that serves as a passageway for the vestibulocochlear nerve (CN VIII). 434

Glossary

Internal branch of the superior laryngeal nerve:  one of two branches of the superior laryngeal nerve, which is a branch of the vagus nerve. Internal carotids:  two large arteries that branch from the common carotid arteries and provide oxygenated blood flow to the medial and anterior brain. Internal intercostals:  a group of muscles located in the intercostal spaces between the ribs, just beneath the external intercostal muscles that assist in forced expiration. Internal oblique abdominis:  an abdominal muscle that forms the middle layer of abdominal musculature between the external oblique abdominis and the rectus abdominis and assists in forced expiration. Interneuron:  a type of neuron that is responsible for conjoining neurons to each other within the same area of the brain. Interspike interval:  the amount of time between individual action potentials (spikes) of a neuron. Intervertebral discs:  the cartilaginous discs located between the vertebrae in the spine. Intervertebral foramina:  the openings between articulating vertebrae between which the roots of the spinal nerves exit the vertebral column. Intonation:  the changes in pitch during an utterance to communicate meaning. Intraoral pressure:  the air pressure within the oral cavity. Intrapleural pressure:  the pressure that exists within the pleural linkage, between the visceral pleura and parietal pleura Intrapleural space:  the airtight cavity between the visceral and parietal pleura, which are the thin membranes that envelop the lungs. Intrinsic auricular ligaments:  the fibrous bands that connect structures of the auricle to each other. Intrinsic laryngeal membrane:  originate from the elastic membrane — a broad sheet of connective tissue that lines most of the interior of the larynx. Intrinsic muscles of the larynx:  responsible for opening and closing of the vocal folds. Intrinsic muscles of the tongue:  muscles that comprise the mass of the tongue and are responsible for fine movement of the tongue. Invasive electrodes:  provide clearer, more precise electrical responses due to the electrodes being in close proximity to the voltage generators but requires medical supervision and the patient to be sedated with anesthesia. Irregular vibration of the vocal folds:  when the vocal folds vibrate in an inconsistent manner. Ischial tuberosity:  a posterior section of the ischium that bears weight of the body in a sitting position. Ischium:  one of three parts of the hip bone, this is the posterior inferior section of bone that bears body weight when sitting and provides a point of attachment for the femur. Isthmus:  a narrow portion of the ear canal or a constricted area in the eustachian tube. Jitter:  a measurement of frequency instability, in cycle-to-cycle fundamental frequency. Joints:  where two bones are attached to allow body parts to move. Jugular vein:  a large blood vessel in the neck that carries blood from the head back to the heart. Kinocilium:  the sensory receptor of the hair cell within the crista ampularis. Kinocilium:  the tallest stereocilia found within each hair cell in the inner ear. Labial surface:  the surface of the anterior-most teeth, the incisors and cuspids, that contacts the inside of the lips. Labyrinthian:  also called the labyrinthine wall; refers to the bony wall of the inner ear that contains the cochlea and the vestibular system. 435

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Lacrimal bones:  the small paired facial bones situated medially within the orbital cavity and named due to their proximity to the tear ducts and other soft tissue structures involved in the production of tears. Lamina propria:  a layer of loose connective tissue that lies beneath the epithelial layer of various organs. It is made up of the superficial, intermediate, and deep layers. Laminae:  the thin, flat, or arched parts of the vertebrae that form the posterior section of each vertebra and, therefore, the posterior of the spinal canal. Laryngopharynx:  also called the hypopharynx; the most inferior division of the pharynx, closely associated with the larynx. Laryngostroboscopy:  a medical procedure used to examine the larynx using a flexible or rigid endoscope that contains a flashing light source, called a stroboscope. Larynx:  a section of the respiratory system located between the pharynx and the trachea. Latency:  the time delay between the onset of the stimulus and the onset of the neural response. Latency intensity function:  a latency function of stimulus intensity that can be used to assess the electrophysiology of the auditory mechanism. Lateral cricoarytenoid muscles:  the paired muscles located in the larynx that connect the cricoid cartilage to the muscular process of the arytenoid cartilage. Lateral cricothyroid membranes:  the thin, fibrous bands of tissue that extend from the superior border of the cricoid cartilage to the inferior portion of the vocal ligaments. Lateral lemniscus:  a neural pathway in the auditory system that plays a key role in relaying information about sound from the cochlear nucleus to the inferior colliculus in the midbrain. Lateral ligament:  a small ligament located in the middle ear, which connects the malleus bone to the lateral wall. Lateral semicircular canal:  one of three semicircular canals found in the inner ear that is oriented roughly horizontally and is positioned at a right angle to the anterior semicircular canal and the posterior semicircular canal. Lateral sulcus:  a deep groove that runs along the lateral surface of the brain and separates the frontal lobe from the temporal lobe. Lateral thyrohyoid ligament:  forms the posterior border of the thyrohyoid membrane and courses through the tip of the superior cornu of the thyroid cartilage and the greater cornu of the hyoid bone. Lateral ventricles:  two symmetrical and large C-shaped cavities beneath the cerebrum that at any moment contain most of the cerebrospinal fluid within the ventricular system. Lateral wall:  the tympanic membrane and only part of the middle ear cavity not enclosed by bone. Latissimus dorsi:  a large superficial muscle of the lower back that is primarily important for movement of the arm. Lentiform nucleus:  a structure of the basal ganglia that is the putamen and globus pallidus. Leptomeninges:  the meningeal layers of the pia mater and the arachnoid mater. Lesion localization:  when a pathologic lesion is observed in the brain and the clinical deficits a person is displaying are then attributed to that part of the brain affected by the lesion. Lesser horns of hyoid:  the two small, bony projections that extend from the superior border of the body of the hyoid bone. Levator anguli oris:  a paired facial muscle that courses inferiorly to insert into the corners of the orbicularis oris from above; functions to raise the corners of the mouth superiorly and medially. Levator costarum:  a group of paired muscles located posteriorly and medially on the ribs on either side of the vertebral column; can function to elevate the rib cage for forced inspiration. Levator labii superioris:  a paired facial muscle that courses inferiorly toward the upper lip at an angle from above and functions to elevate the upper lip. 436

Glossary

Levator labii superioris alaeque nasi:  a paired facial muscle that courses inferiorly at a vertical angle and inserts into the upper lip and functions to elevate the upper lip. Levator scapulae:  a paired muscle located at a posterior lateral location on the neck; functions to stabilize and elevate the scapula. Lever:  when a pivot point is close to the unit being displaced, such as the ossicular chain. Linea semilunaris:  a curved tendon on either side of the rectus abdominis providing a point of attachment for lateral abdominal muscles. Lingual frenulum:  a band of epithelial tissue that runs from the underside of the tongue to the floor of the oral cavity. Lingual septum:  the fibrous tissue that runs longitudinally in the tongue and is the medial point of attachment for muscle of the tongue. Lingual surface:  the surface of the teeth that comes into contact with the tongue. Lingual tonsils:  large, bumplike structures of lymphoid tissue on the base of the tongue. Lips:  the anterior-most boundary of the oral cavity formed by a layer of transparent epithelial tissue, which reveals the red-colored vascular tissue beneath. Longitudinal muscles of the pharynx:  the group of pharyngeal muscles that course vertically within the pharynx and function to elevate the pharynx during deglutition. Loose connective tissue:  found throughout the body and attaches epithelial tissue to other tissues and keeps the organs in place. Loudness:  the perceptual correlate of both amplitude and intensity. Low-frequency sounds:  generate a longer traveling wave that moves toward the apex of the cochlea. Lower esophageal sphincter (LES):  a ring of muscle located at the junction between the esophagus and the stomach that controls admittance of the bolus from the esophagus into the stomach. Lower respiratory system:  the organs that are responsible for the exchange of gases between the body and the environment. Lower respiratory tract:  the respiratory passages below the larynx; from superior to inferior these include the trachea and all branches of the bronchial tree down to the alveoli. Lumbar vertebrae:  the largest of the vertebrae and are inferior to the thoracic vertebrae and superior to the sacral vertebrae. Lumbodorsal fascia:  a fibrous sheet of connective tissue located in the lower back region of the body; provides a point of attachment between the external and internal oblique abdominis, transversus abdominis, and the vertebral column. Lung volumes:  individual and separate divisions of the total amount of air that the lungs are capable of containing. Lungs:  the primary organs of respiration; house the major passages and structures that allow the human body to absorb oxygen and release carbon dioxide. Lymphatic system:  a network of tissues, organs, and vessels that helps to defend against infections, maintain fluid balance, and absorb and transport dietary fats. Macroscopic anatomy:  the study of gross anatomy that uses unaided eyesight to study parts of an animal’s body. Macrostructure processing:  the ability to recognize smaller details and, perceiving how many smaller details fit together, arrive at an understanding of the whole. Macula (plural:  maculae):  specialized sensory organs located within the utricle and saccule of the inner ear. Maculae:  the specialized sensory organs located within the utricle and saccule of the inner ear; responsible for sensing acceleration of the head. 437

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Malleolar folds:  located on either side of the pars flaccida separating it from the pars tensa. Malleus:  the first and largest of the ossicles resembling a hammer that is attached to the tympanic membrane via fibers of connective tissue. Mammillary bodies: the small bodies of nuclei in front of the thalamus that share connections with the hippocampus and are involved in spatial and episodic memory. Mandible:  the jawbone; houses the inferior dental arch and articulates with the skull at the temporomandibular joint. Mandibular hypoplasia:  a congenital condition featuring a small, underdeveloped mandible. Manometry:  the measurement of pressure within the respiratory system using a manometer. Manubrium sterni:  the superior-most portion of the sternum. Masticatory central pattern generator:  a group of nuclei in the brainstem that is responsible for generating and coordinating the rhythmic movements of the mandible during mastication. Matrix:  the extracellular substance that is present between cells in the body. Maxillae:  paired bones of the face that form the upper dental arch, the roof of the mouth, the base and the lateral portions of the nasal cavity, and also a small portion of the orbital cavity. Mechanical energy:  sets into motion the fluid of the inner ear. Medial geniculate body:  the location where all afferent nerve fibers synapse at in the thalamus. Medial sulcus:  the midline longitudinal crease on the tongue. Median cricothyroid ligament:  a thin, fibrous membrane that connects the thyroid cartilage to the cricoid cartilage in the larynx in the neck. Medulla:  the inferior-most portion of the brainstem. Membranous ampullae:  the structures located within the semicircular canals of the inner ear. Membranous labyrinth:  composed of the cochlear duct, utricle, saccule, and membranous semicircular canals all located in an osseous labyrinth within the inner ear. Membranous semicircular canals:  located within the osseous semicircular canals, they connect to the utricle in the vestibule of the inner ear via five orifices. Meninges:  the outermost membranes that cover the brain and spinal cord; they are made up of connective tissue. Meningitis:  an infection and inflammation of the meninges. Mental protuberance:  the medial bony projection at the base of the chin where the mental symphysis is divided. Mental symphysis:  the medial point of fusion of the two halves of the mandible. Mental tubercles:  the depression on the mandible at midline with raised bony projections on either side. Mentalis:  a muscle of the face that courses superiorly from the medial portion of the mandible into the inferior lip from below; functions to wrinkle the chin and raise the lower lip. Mesothelium:  the type of epithelial cell type that composes the lining of many cavities of the body. Microbial physiology:  the study of bacteria, parasites, viruses, and fungi. Microglia:  smaller immunological glial cells of the central nervous system that account for 10% to 15% of the brain. Microscopic anatomy:  a type of anatomy that allows clinicians to use optical methods to observe structures and tissues inside a living person without dissection. Microtia:  misshapen pinna. Midbrain:  the superior-most portion of the brainstem. Middle cerebellar peduncles:  one of three neural structures known as peduncles that connect the cerebellum to the brainstem; largely receive motor signals in need of refining from the cerebrum to the cerebellar hemispheres. 438

Glossary

Middle cerebral arteries:  a pair of arteries that supply blood to the medial lateral surface of the brain. Middle cricothyroid ligament:  the yellow, elastic tissue that is strong and thick and connects the front parts of the contiguous margins of the thyroid and cricoid cartilages. Middle scalenes:  the medial and largest pair of scalene muscles that can function to elevate the first rib for inspiration or tilt the head. Middle thyrohyoid ligament:  a fibrous band of tissue that connects the thyroid cartilage to the hyoid bone. Mixed dentition stage:  the period of time during which a child has a mixture of deciduous and permanent teeth. Mixed hearing loss:  the result of coexisting conductive and sensorineural hearing loss. Mobile articulators:  the structures of the vocal tract involved in articulation of speech that move for production of speech. Modal register:  used during everyday speech, where the vocal folds are neither relaxed nor stretched. Mode of vocal fold vibration:  a precise pattern in which the vocal folds can move during a vibratory cycle; usually restricted within a particular pitch range. It also creates the vocal register. Modiolus:  a cone-shaped bony structure located at the center of the cochlea. Molars:  the largest of the teeth that are the primary grinders of food. Monoloud:  a speaking or singing voice that lacks variation in loudness. Monophthong:  a vowel phoneme with a single constant perceived quality due to an unchanging single tongue position. Monopitch:  a speaking or singing voice that lacks variation in pitch. Morbid anatomy:  the study of diseased tissues. Motor homunculus:  a visual representation of the volume of cortex within the primary motor cortex devoted to the control of each body part. Motor neuron:  a type of neuron that is responsible for transmitting impulses of motor movement. Motor unit:  is made up of a single motor neuron and also all of the individual muscle fibers innervated by single motor neurons. Mucosal wave:  also called the traveling wave; the superficial tissue of the vocal folds that can vibrate laterally, longitudinally, or vertically. Mucous layer:  the innermost layer of the tympanic membrane that is continuous with the mucosal lining of the rest of the ear. Muscles of mastication:  a group of muscles that are important for the movement of the mandible. Muscles of the face:  a group of muscles that are responsible for facial expression and contribute to articulation of speech and mastication. Muscles of the velum:  a group of muscles responsible for either elevating or depressing the velum. Muscular process:  a part of the arytenoid cartilage; a projection on the lateral surface of each arytenoid cartilage. Muscular system:  the collection of muscles in the body that are responsible for various movements and activities. Myelin:  a fatty substance that forms a protective cover around the axons of nerve cells in the nervous system. Mylohyoid:  a paired muscle located in the floor of the mouth, forming the base of the oral cavity. Myoelastic-aerodynamic theory:  the vibration of the vocal folds is dependent on muscle action, elasticity, pressure, and airflow. Myofibrils:  the contractile units of muscle cells that are made up of thousands of long filaments found in muscle fibers that contain actin and myosin. Myoglobin:  a protein that binds oxygen to muscle fiber. 439

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Myringotomy:  a surgical procedure in which a small incision is made in the tympanic membrane to relieve pressure or to drain fluid that has accumulated in the middle ear. Nares:  the anterior opening of the nasal cavity at the face. Nasal bones:  the two narrow and long bones that are fused at the midline to create the bridge of the nose. Nasal cavity:  a large air-filled space within the skull that is lined with mucous membranes and cilia and constitutes part of the upper respiratory tract. Nasal choanae:  the point at which the nasal cavity opens into the pharynx posteriorly. Nasopharynx:  the superior-most portion of the pharynx located behind the nasal cavity and above the velum. Neck of the rib:  the portion of the rib that exists between the ribs’ terminal attachments at the corpus of the thoracic vertebrae and the secondary attachment of the rib on the transverse process of the thoracic vertebrae. Neck of the tooth:  the point at which the crown and root of the tooth meet. Nerves:  transmit signals between the brain and other parts of the body. Nervous system:  a complex network of specialized cells, tissues, and organs that coordinate and control the activities of the body. It is made up of nerves, the brain, and the spinal cord. Neuroglia:  several types of nervous system cells that act to provide important structural and physiological support to neurons but are not involved in transmitting or processing information. Neuron:  also called a nerve cell; a specialized cell that is the central unit of the nervous system. Neurotransmitters:  chemical messengers that allow neurons to communicate with each other and with other cells in the body. Noninvasive electrodes:  can be used to measure electrical activity in the body without penetrating the skin or mucous membrane. Nonlinear source-filter coupling theory:  the pressure changes in the filter influence the production of frequencies by the source. Oblique arytenoid muscles:  paired muscles located in the larynx that connect the muscular process of one arytenoid cartilage to the apex of the opposite arytenoid cartilage. Occipital lobes:  the posterior-most lobes of the cerebrum; primarily responsible for processing visual information. Occlusal surface:  the surface of the teeth where the teeth of the upper and lower dental arches come into contact with one another when the mandible is raised. Occlusion:  the act of raising the mandible to bring the upper teeth into contact with the lower teeth. Oligodendrocytes:  neuroglia that produce the myelin sheath on axons in the central nervous system. Omohyoid:  a long, slender muscle located in the neck region of the human body. Optic chiasm:  the point at which the left and right optic nerves come together, and the medial fibers from each nerve decussate (cross over) to the opposite side to continue within the brain along the optic tract on the way to the occipital lobe where visual information is processed. Optic tract:  the continuation of the optic nerve fibers through the brain. Optimal pitch:  the ideal frequency of vocal fold vibration that requires the least amount of effort for an individual. Oral cavity:  the mouth; a part of the digestive tract and is where food enters the body but is also an important part of the respiratory tract and is vital for articulation of speech. Oral preparatory stage:  the first stage of the swallowing process where food or liquid is placed in the mouth and is manipulated, masticated, and readied into a bolus. 440

Glossary

Oral stage:  the second stage of the swallowing process where the tongue transports the bolus posteriorly toward the pharynx, triggering the pharyngeal swallow. Orbicularis oculi:  a paired muscle of the face that aids in gently closing the eyelids when blinking, firmly closing the eyelids when winking, and drawing tears to the eyes. Orbicularis oris:  the sphincter muscle that is located within the lips and comprises oval-shaped fibers that circle the mouth; responsible for puckering the lips and pressing the lips together. Organ of Corti:  also called the spiral organ; a sensory organ located in the cochlea responsible for hearing; contains specialized sensory cells that convert sound waves into electrical signals. Organelles:  specialized structures within cells that are responsible for tasks such as creating proteins to generate energy for the cell. Cells have a finite life span. Organs:  groups of tissues that work together to perform a specific function within the body. Origin:  the fixed point of attachment of a muscle. Oropharynx:  the section of the pharynx posterior to the oral cavity. Os coxae:  the bone of the hip or hip bone; made up of the ilium, ischium, and pubic bones. Oscillator:  a device or circuit that produces a periodic, repetitive waveform or signal. Osseous (bony) labyrinth:  the bony outer shell that surrounds and protects the delicate membranous labyrinth of the inner ear. Osseous semicircular canals:  three bony channels that are located within the inner ear and are a part of the vestibular system. Osseous spiral lamina:  located in the cochlea; two bony plates that extend outward from the modiolus that splits the cochlea into the scala vestibuli and tympani. Ossicular chain:  a group of three small bones (ossicles) located in the middle ear that transmit sound waves from the tympanic membrane to the inner ear. Osteoblasts:  cells that help with forming new bones when there are fractures. Otitis media:  an infection or inflammation of the middle ear. Otoacoustic emissions (OAEs):  sounds that echo back and can be measured in the middle ear space. Otolithic membrane:  a gelatinous layer that covers the sensory hair cells in the utricle and saccule of the inner ear. Otoliths:  the small, calcium carbonate crystals that are found in the otolithic membrane of the utricle and saccule. Otosclerosis:  abnormal bone growth usually around the footplate of the stapes. Otoscope:  a handheld light source commonly used to examine the tympanic membrane. Ototoxic drugs:  medications that have harmful effects on the inner ear. Outer hair cells (OHC):  a type of sensory cell found in the cochlea. They are named for their location in the outermost layer of the cochlea and for the presence of small hairlike projections on their surface, which help amplify sound waves and increase the sensitivity of the inner ear. Oval window:  a small, oval-shaped membrane located at the base of the cochlea in the inner ear; one of two openings through which sound waves enter the cochlea. Overjet:  how far anterior the maxillary incisors are to the mandibular incisors. Pain withdrawal reflex:  a spinal reflex that is shown when an extremity is retracted from a painful stimulus. Paired cartilages:  include the arytenoid, corniculate, and cuneiform cartilages. Palatal aponeurosis:  a piece of tendinous fibrous tissue arising from the posterior hard palate and coursing through the length of velum. Palatal rugae:  a series of small ridges on the anterior hard palate. Palatine bones:  the complex small bones on the posterior of the maxillae forming the posterior portions of walls of the nasal cavity, part of the orbital cavity, and the posterior one third of the hard palate. 441

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Palatine process:  the portion of each maxilla creating the anterior two thirds of the hard palate. Parallel muscles:  the superficial muscles of the integument in the region of the mouth that course parallel to the orbicularis oris. Parietal bones:  paired bones of the medial cranium that overly the parietal lobes of the brain. Parietal lobes: posterior to the frontal lobes; responsible for receiving and processing signals of somatosensation. Parietal pleura:  thin layers of pleura that line the inside of the thoracic cavity. Pars flaccida:  superior region of the intermediate layer of the tympanic membrane that moves outward for pressure equalization. Pars tensa:  the thicker, tougher, and more central part of the tympanic membrane located below the pars flaccida. Passive expiration:  expiration using only the passive forces of gravity and the recoil of elastic tissues of the lungs and thorax to return the thorax to a position of rest after being displaced during inspiration. Peak amplitude:  the maximum displacement of the basilar membrane in response to a sound stimulus. Pectoral girdle:  consists of the clavicle and scapula and is the point of origin of some accessory muscles of respiration and is the point of connection of the arm to the rest of the skeleton. Pectoralis major:  a large, fan-shaped muscle of the chest; located anteriorly and superficially on the thorax and can assist in expanding the rib cage anteriorly and superiorly for forced inspiration. Pectoralis minor:  small muscle that occurs on the anterior superior thorax beneath the pectoralis major; can assist in elevating the rib cage for forced inspiration. Pedicles:  the paired bony processes that project posteriorly from the corpus of each vertebra and fuse with the laminae to constitute the vertebral foramen. Peduncles:  three neural structures connecting the cerebellum to the brainstem. Pelvic girdle:  also called the hip girdle; a ringlike structure that is made up of bones that connect the axial skeleton to the lower limbs; provides the skeletal framework that connects the lower extremities (the legs) to the vertebral column. Penetration:  when foreign material passes into the airway but does not pass below the true vocal folds. Perforated tympanic membrane:  hole in the tympanic membrane. Perfusion:  the process of the circulatory system delivering oxygenated blood to the capillaries surrounding body tissues, such as the alveoli of the lungs. Perilymph:  a fluid high in sodium and calcium that fills the scala tympani and scala vestibuli. Perilymphatic space:  the space between the wall of the bony labyrinth and the membranous labyrinth of the vestibular system filled with perilymph. Perimysium:  a connective tissue that separates groups of muscle fibers from one another and permits muscle function as a single unit. Period of vibration:  the time it takes to complete one cycle of vibration. Periodic:  vibration repeats itself during each cycle. Periosteum:  a dense layer of fibrous connective tissue that covers the outer surface of bones, except for the joint surfaces where cartilage is located. Peripheral nervous system:  the portion of the nervous system that is made up of the sensory and motor nerve tracts that course between the central nervous system and the rest of the body. Perturbation:  a disturbance in the regularity of a waveform; correlates to a harsher vocal quality. Phalangeal cells:  support the bases of the inner hair cells in the ear. Pharyngeal constrictor muscles:  the muscles of the pharynx that constitute the walls of the pharynx and are responsible for pharyngeal constriction. Pharyngeal peristalsis:  the coordinated muscular contractions of the walls of the pharynx that guide and propel the bolus over the airway and inferiorly to the esophagus. 442

Glossary

Pharyngeal plexus:  a network of nerves that innervates the muscles of the pharynx and soft palate, which are involved in swallowing and speech production. Pharyngeal raphe:  a fibrous ligament at posterior midline on the pharynx where the pharyngeal constrictors insert. Pharyngeal stage:  the third stage of the swallowing process that begins as the pharyngeal swallow is triggered and the bolus is moved through the pharynx to the esophagus. Pharyngeal stasis:  the bolus residue remaining in the pharynx after deglutition. Pharynx:  a muscular tube that exists posterior to the nasal cavity and oral cavity. Philtral pillars:  the raised vertical columns that are on either side of the philtrum. Philtrum:  the medial and vertical indentation that runs from the nasal septum to the upper lip. Phonation:  the production of sound by the vibration of the vocal folds in the larynx. Phonation threshold pressure:  the minimum amount of pressure necessary to sustain vibration of the vocal folds. Phonatory:  the process of producing sound by the vocal folds in the larynx during speech or singing. Phonatory system:  the anatomical structures and physiological processes involved in the production of sound in human speech. Phrenic nerve:  the spinal nerve that originates in the cervical area of the spinal cord and is the sole provider of efferent signal to the diaphragm. Physiology:  the study of the functions of living organisms and their parts. Pia mater:  the innermost and most fragile layer of the meninges. Pillar cells:  the supporting cells that form the tunnel of Corti located between the inner and outer hair cells. Pinna:  is shaped like a funnel and has various grooves and folds; it serves to localize and collect sound and guide it into the ear canal. Pitch:  the perceptual correlate of frequency. Pitch range:  the difference between the highest and lowest frequencies produced by a specific set of vocal folds. Pituitary gland:  a small gland located at the base of the brain known as the master gland because it controls most other glands in the body. Plant physiology:  the study of the functioning of plants. Pleural linkage:  the airtight coupling between the lungs and the wall of the thoracic by the pleural membranes. Pleural membranes:  the delicate external lining of the lungs (visceral pleura) and internal lining of the thoracic cavity (parietal pleura). Polyps:  abnormal growths that can occur on the lining of the vocal folds in the larynx. Pons:  the middle portion of the brainstem. Posterior cerebral arteries:  a pair of arteries that arise from the basilar artery at the base of the brain and supply the posterior portion of the brain. Posterior communicating arteries:  a pair of arteries that connect the posterior cerebral arteries to the internal carotid arteries in the brain. Posterior cricoarytenoid muscle:  the muscle located in the larynx that abducts the vocal folds and rotates the arytenoid cartilages. It is the only muscle involved in opening the vocal folds for normal breathing. Posterior gap:  the vocal fold closure pattern if there is a gap near where the vocal folds attach to the arytenoid cartilages at the vocal process. Posterior ligament:  suspends the short process of the incus. Posterior quadrate lamina:  located on the superior surface of the cricoid cartilage; connects with the arytenoid cartilages. 443

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Posterior scalenes:  the smallest and posterior-most pair of scalene muscles; can function to elevate the second rib to assist in forced inspiration or the tilting of the head to one side. Posterior semicircular canal:  oriented vertically; located in the posterior portion of the bony labyrinth of the inner ear. Posterior thorax:  the dorsal side of the thorax. Posterior wall:  also called the mastoid wall; one of the four walls of the middle ear cavity that is wider at the top than the bottom. Postlingual hearing loss:  hearing loss that occurs after the acquisition of speech and language. Postsynaptic neuron:  the neuron that is receiving the signal across the synapse. Potassium ions:  positively charged ions that are essential for many physiological processes in the human body, including nerve impulse transmission and muscle contraction. Power:  generated from the lungs. Power for voice:  the strength or loudness of the sound produced by the vocal folds. Prefrontal cortex:  the anterior-most portion of the paired frontal lobes responsible for higher level cognitive skills, executive functioning, initiation of movement, and inhibition of inappropriate social impulses. Prelingual hearing loss:  hearing loss that occurs before the acquisition of speech and language. Premaxilla:  the anterior-most and medial division of the hard palate formed by the maxillae. Premaxillary suture:  the point where the bones of the maxilla meet to form the premaxilla. Presbycusis:  hearing loss due to normal age-related changes in the inner ear. Presbyphagia:  age-related changes in swallowing function that can lead to difficulties in mastication and deglutition. Presynaptic neuron:  the neuron that is transmitting an action potential toward the synapse. Primary auditory cortex:  a region in the superior temporal lobes that houses Heschl gyrus and receives afferent signals of audition from the ears. Primary bronchi:  the first and largest respiratory passages that branch from the trachea. Primary motor cortex:  the posterior-most gyrus of the frontal lobes that is responsible for the initiation and control of voluntary movement in the body. Primary muscles of expiration:  the muscles that are associated with the abdomen and are involved in pushing the viscera up into the diaphragm to reduce the vertical dimension of the thorax for expiration. Primary sensory cortex:  the anterior-most gyrus of the parietal lobes that is responsible for processing and interpreting somatosensation. Primary tissues:  epithelial tissue, connective tissue, muscle tissue, and nervous tissue. Primary visual cortex:  the posterior-most portion of the occipital lobes that receives and processes visual information from the eyes. Prime movers:  the muscles that permit specific movements, also known as agonists. Procerus:  a muscle involved with wrinkling at the root of the nose. Promontory:  a rounded protuberance shaped by the basal turn of the cochlea located between the oval and round windows. Prosody:  the changes in tone, stress, and intonation pattern that give speech an emotional component. Prosopagnosia:  the deficit in the ability to recognize familiar faces. Protective redundancy:  ensures that even if one side of the nervous system is damaged or disrupted, the other side can still maintain some degree of control over the organ or tissue. Pterygomandibular raphe/ligament:  a band of ligament coursing between the sphenoid bone and the mandible. Pubic bone:  one of the three main bones that constitute the bone of the hip and is the inferior and anterior bony portion of the pelvic girdle. 444

Glossary

Pubic symphysis:  a midline joint where the left and right pubic bones meet. Pulmonary arteries:  a pair of arteries that carry deoxygenated blood from the heart to the lungs for oxygenation. Pulmonary veins:  the veins that transport oxygenated blood from the lungs to the heart. They are the only veins in the body that carry oxygenated blood. Pulp:  the inner matter of teeth that contains associated soft tissue such as blood vessels and nerves. Pure tone audiometry:  measures air and bone conduction thresholds and can be used to diagnose conductive, sensorineural, or mixed hearing loss. Pyramidal decussation:  the point where the many motor neuron fibers descending through the central nervous system cross over from one side of the medulla to the opposite side of the medulla allowing for contralateral innervation. Pyramidal eminence:  a small, triangular-shaped elevation located on the medial wall of the middle ear cavity. Pyriform sinus:  the small spaces located between the mucous lining of the thyroid cartilage and the aryepiglottic folds. Quadrangular membranes:  made up of collagen and elastic fibers and contain the cuneiform cartilages. Quadratus lumborum:  a deep posterior muscle of the abdomen that courses between the pelvis and the last rib and first four lumbar vertebrae and can function to retract the rib cage for expiration. Quiet inspiration:  the level of inspiration that is necessary to maintain life with minimal energy exerted. Quiet respiration:  the most and natural efficient pattern of respiration as a person is breathing softly with the body exerting little physical effort; involves quiet inspiration and passive expiration. Radiological anatomy:  the use of fluorography and radiography to study anatomy. Rami:  the perpendicular/vertical portion of the mandible. Rarefaction:  a decrease in air pressure in a sound wave that occurs when the air particle is moving back to equilibrium. Rectus abdominis:  a paired flat muscle that extends across the anterior of the abdomen, is divided into sections of muscle, and can function to compress the abdomen for forced expiration. Recurrent laryngeal nerve:  a branch of the vagus nerve that supplies motor innervation to all of the muscles of the larynx except for the cricothyroid muscle. It innervates the laryngeal muscles, including the vocal folds. It is called “recurrent” because it wraps around the aortic arch (on the left side) or subclavian artery (on the right side) before returning upward to the larynx. Reflex:  a simple motor response generated by the brainstem or possibly spinal cord automatically (beneath the level of awareness) in response to incoming sensory stimuli. Regular vibration of the vocal folds:  when the vocal folds vibrate in a consistent manner. Reinke edema:  a condition in which the vocal folds become swollen and filled with fluid. Reissner membrane:  a thin, delicate membrane located within the cochlea, specifically in the scala media. It separates the scala media from the scala vestibuli. Reproductive system:  a collection of tissues and organs that work together to facilitate sexual reproduction. Residual volume:  the amount of air that is always retained in the lungs and cannot be pushed out during expiration. Resonance:  the process by which an air-filled cavity, or a container of air, inhibits certain sound frequencies while reinforcing other frequencies based on physical properties of the container such as volume and length. Resonant frequency:  when a certain structure vibrates in response to a specific frequency. 445

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Resonators:  all the structures above the vocal folds. Respiration:  the process of inhaling air into the lungs and exhaling it out of the body. Respiratory center:  a specialized neural network located within the medulla and pons of the brainstem that is responsible for generating and monitoring autonomic respiration. Respiratory passages:  the tissues and structures that are directly responsible for exchange of gases and through which air moves during the process of respiration. Respiratory system:  a collection of tissues and organs that work together to facilitate the exchange of gases between the body and the environment. Respiratory zones:  the last few divisions of the bronchial tree that contain alveoli and where gas exchange occurs. Resting potential:  the electrical potential difference across a cell membrane when the cell is at rest and not generating electrical impulses. Reticular activating system:  important structures that together work to regulate the level of wakefulness and arousal and other autonomic functions such as blood pressure and respiration. Reticular membrane:  a fragile membrane made of phalangeal cells that stereocilia project through. Risorius:  a paired muscle of the face that functions to retract the corners of the mouth posteriorly. Roof:  also called the tegmental wall; the upper wall of the middle ear composed of a thin layer of bone, which separates it from the brain cavity above. Root:  inferior bony projections of teeth below the gingival line. Round window:  an opening in the bony wall of the cochlea of the inner ear located below the oval window and covered by a thin, flexible membrane. Rubella:  German measles. Saccule:  a small, fluid-filled sac located in the vestibule of the inner ear that resides on the medial wall of the membranous labyrinth and connects to the cochlea through the ductus reuniens. Sacral vertebrae:  the four to five fused vertebrae that form the sacrum. Sacrum:  a triangular-shaped bony structure located at the base of the vertebral column and between the bones of the hip. Sagittal/vertical plane:  divides the body into right and left sides vertically. Salivary glands:  the tissues that produce saliva in the oral cavity for the oral preparation of food prior to a swallow to maintain appropriate oral hygiene. Scala media:  also called the cochlear duct; an endolymph-filled cavity that is located in the cochlea and contains hair cells. Scala tympani:  one of the three fluid-filled chambers that make up the cochlea in the inner ear, filled with perilymph. Scala vestibuli:  the upper passageway of the cochlea, filled with perilymph. Scalenes:  a group of three pairs of neck muscles deep to the sternocleidomastoid muscle with the primary function of stabilizing, tilting, and rotating the head. Scaphoid fossa:  the depression between the helix and antihelix. Scapula:  a thin, flat, and triangular bone that is also known as the shoulder blade and is the posterior portion of the pectoral girdle. Schindylesis:  a joint type where two bone surfaces are interlocked tightly, without an intervening articular cartilage or synovial membrane present. This joint is located between the vomer and the perpendicular plate of the ethmoid bone. Schwann cell:  neuroglia that produces the myelin sheath on axons within the peripheral nervous system. Secondary bronchi:  the first subdivision of the primary bronchi.

446

Glossary

Secondary tympanic membrane:  a thin, flexible membrane that separates the middle ear from the scala tympani. Selective enhancement:  when the pinna augments certain sounds like a microphone but dampens sounds due to its shape. Semilunar notch:  the depression in bone between the condylar and coronoid processes of the mandible. Sensorineural hearing loss (SNHL):  the product of damage to the inner ear or the pathways of CN VIII leading to the brain; may be frequency specific depending on the etiology. Sensory homunculus:  a visual representation of the volume of cortex in the primary sensory cortex dedicated to receiving somatosensation from each body part. Sensory neuron:  neurons responsible for transmitting afferent/sensory information. Serratus anterior:  a fan-shaped muscle positioned laterally on the thorax that can assist in elevating the rib cage for forced inspiration. Serratus posterior inferior:  a quadrilateral muscle of the lower back that can assist in retracting the rib cage for forced expiration. Serratus posterior superior:  a thin and superficially situated muscle of the upper back that can function to elevate the rib cage for forced inspiration. Shaft of the rib:  the thin flat section of bone convex on the external surface and concave on the internal surface; makes up most of the mass of the rib. Shearing action:  when the outer hair cells shift in relation to the tectorial membrane as the wave travels along the basilar membrane. Shimmer:  the measurement of amplitude instability, in cycle-to-cycle fundamental frequency. Simultaneous vocal attack:  adduction of the vocal folds and the initiation of expiration occur simultaneously. Sine wave:  smooth, continuous waveform. Skeletal (striated) muscle:  a type of muscle tissue that is attached to bones and enables movement of the skeleton. Skeletal system:  a complex system that is made up of cartilage, ligaments, bones, and other connective tissues. Smooth (nonstriated) muscle:  a type of muscle tissue that lines the walls of internal organs and structures such as blood vessels, airways, and the digestive tract. Soma:  the portion of the neuron that contains the nucleus. Somatosensation:  the group of sensory modalities originating from the body responsible for body sensation. Sound intensity:  the amount of power transferred by sound waves per unit area in a direction perpendicular to that area. Source:  the location of vocal fold vibration. Source-filter theory of vowel production:  the process of cavities of the vocal tract suppressing certain frequencies of the raw phonatory signal while propagating other frequencies to produce a varying spectrum of possible vowels. Speech audiometry:  a type of hearing test that assesses a person’s ability to hear and understand speech. Speech breathing:  a forced respiration pattern that is used to volitionally commandeer the respiratory system to produce speech sounds. Speech perception:  the understanding of complex features of speech. Speech reception threshold (SRT):  the softest level at which an individual can hear speech 50% of the time. Sphenoid:  a large, unpaired bone of the base of the skull.

447

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Spikes:  action potentials. Spinal cord:  an elongated tubular piece of tissue made of gray and white matter tracts housed by the vertebral column. Spinal nerves:  the 31 paired nerves of the peripheral nervous system arising from the spinal cord. Spinal reflexes:  a simple motor response generated by the spinal cord automatically in response to incoming sensory stimuli. Spindle shape:  incomplete vocal fold closure along the entire length of the vocal folds. Spinous process:  a bony projection that courses posteriorly from each vertebra and provides a point of attachment for muscles. Spinous process of the scapula:  a triangular bony projection on the dorsal surface of the scapula at the junction of its upper one third and lower two thirds. Spiral ganglion:  a group of nerve cells located in the modiolus whose axons extend into CN VIII and are responsible for transmitting auditory information from the hair cells of the cochlea to the brain. Spiral ligament:  attaches the basilar membrane to the lateral wall of the osseous spiral lamina. Spiral limbus:  a collection of connective tissue that lies on the spiral lamina and connects to Reissner membrane. Spirometry:  the measurement of volumes and capacities of the respiratory system using a device called a spirometer. Standard anatomical position:  where the body is at rest and standing erect with the feet together or slightly apart. The face is directed forward. The arms are at the side and rotated outward, with the palms facing forward. The thumbs are pointed away from the body. Stapedius:  one of the two main muscles of the ossicular chain that helps to stiffen the ossicular chain to play a key role in acoustic reflex. Stapes:  the smallest ossicle shaped like a stirrup that connects and transmits sound vibrations to the oval window of the inner ear. Stenosis:  occurs when the ear canal is excessively narrow. Stereocilia:  the tiny, hairlike structures found on the sensory cells (hair cells) of the inner ear, specifically in the cochlea and vestibular system. They are important for detecting and transmitting auditory and vestibular information to the brain. Sternoclavicular joint:  the point at which the clavicle articulates with the sternum. Sternocleidomastoid:  a paired muscle located anteriorly and laterally on the neck that functions to rotate the head or elevate the rib cage for forced inspiration. Sternohyoid:  a thin, straplike muscle located in the neck region of the human body. It depresses the hyoid and the larynx. Sternothyroid:  a thin, paired muscle located in the neck region of the human body. It depresses the thyroid cartilage and the larynx. Sternum:  also known as the breastbone; the prominent anterior and midline structure of the bony thorax that provides a point of attachment for the clavicles and for many ribs. Stiffness:  the degree to which a material resists a deforming force. Stress:  the emphasis given to a word or syllable in a phrase or sentence through the use of an increase in fundamental frequency, intensity, and duration. Stria vascularis:  a highly vascularized, epithelial structure located in the lateral wall of the cochlea in the inner ear. Stylohyoid:  a slender, paired muscle located in the neck region of the human body. It elevates the larynx and initiates a swallow. Subclavius:  a short muscle of the shoulder located between the clavicle and the first rib that is deep to the pectoralis major and can function to assist in elevating the rib cage for forced inspiration. 448

Glossary

Subcortex:  the portion of the brain that lies below the cerebral cortex. Subcostals:  a muscle group situated deep to the internal intercostals on the interior surface of the wall of the posterior thorax; can assist in expiration. Subglottal pressure:  the air pressure below the glottis. Subglottic space:  the area below the level of the vocal folds. Submucous fibrous layer:  a layer of connective tissue in the tongue that provides a superficial attachment point for muscles of the tongue. Substantia nigra:  a paired dark structure of the midbrain and part of the basal ganglia where the neurotransmitter dopamine is produced. Successional teeth:  the permanent teeth that have deciduous teeth that they are similar to and are replacing. Sucking feeding pattern:  a later and more volitional and more sophisticated pattern of infant feeding. Suckle feeding pattern:  an early reflexive feeding pattern observed in newborns. Sulcus terminalis:  a V-shaped groove in the tongue made where the dorsum of the tongue meets the lingual tonsils. Summating potential (SP):  an electrical potential generated by the cochlea in response to a sound stimulus. Superadded teeth:  the permanent teeth that do not have deciduous analogues. Superficial anatomy:  the study of external structures of the body. Superficial lamina propria:  a layer of connective tissue that lies just beneath the epithelium in some tissues, particularly in the respiratory and digestive tracts. Superficial layer of squamous epithelium:  the outermost layer of cells in a stratified squamous epithelium. Superior cerebellar peduncles:  one of three neural structures known as peduncles that connect the cerebellum to the brainstem; functions to transmit outgoing information from the cerebellum back to the central nervous system to then be sent efferently to the body for execution of movement. Superior colliculus:  a structure located in the midbrain that is involved in the processing of visual and auditory sensory information. Superior laryngeal nerve:  a branch of the vagus nerve that supplies the muscles of the larynx and the sensation of the larynx above the vocal folds. It divides into two branches:  internal and external. Superior ligaments:  located in the middle ear; hold the epitympanic recess to the head of the malleus and attach the incus to the epitympanic recess. Superior olivary complex (SOC or superior olive):  a group of nuclei located in the brainstem, specifically in the pons, that is involved in the processing of auditory information from both ears. Superior temporal gyrus (STG):  a region of the cerebral cortex located in the temporal lobe of the brain involved in various functions, including auditory processing, language comprehension, and memory. Supplementary muscles:  facial muscles assist in performing movements of the structures of the face superior to the mouth. Suprasegmental properties of speech:  include pitch, prosody, intonation, and variations of loudness. Surface anatomy:  the study of the surface of human body structures. Surfactant:  a lubricating substance that is produced by the body between the pleural membranes. Sustained phonation:  phonation that is steadily held out for a relatively long duration at a specific tone. Suture or seam:  found only in the skull; immovable joints that occur between the bones of the skull. Swallowing central pattern generator:  the group of nuclei located in the medulla of the brainstem that are responsible for the coordinated sequential movements of the pharyngeal swallow. Symphysis:  a joint in the body where two bones are connected by a fibrocartilaginous pad or disc. This joint allows for restricted movement and is responsible for cushioning and absorbing shock and pressure. 449

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Synapse:  a specific point of contact that enables information exchange between two neurons, or between a neuron and a target cell such as a gland or muscle cell. Synaptic cleft:  the space between the presynaptic axon and postsynaptic dendrite. Synaptic transmission:  the exchange of electricity or the exchange of both chemicals and electricity between neurons. Synarthrodial joints:  types of joints in the body that have very little or no mobility. Synchondrosis:  an unmoving joint where the connecting tissue is hyaline cartilage. Syndesmosis:  a minimally movable joint that allows for restricted movement while offering support and stability to the bones. Synovial fluid:  a clear, viscous liquid that is found in the cavities of synovial joints, such as the knee, hip, and elbow joints. Synovial joints:  joints of the body that are characterized by smooth gliding cartilaginous surfaces lubricated between by a viscous fluid (synovial fluid). Synovial membrane:  a thin layer of tissue that lines the inner surface of synovial joints and forms a capsule around the joint. It produces synovial fluid, which lubricates and nourishes the joint and provides nutrients and oxygen to the joint cartilage. Syphilis:  a bacterial infection usually spread by sexual contact. Taste buds:  the specialized sensory organs of taste located on the tongue and the palatal epithelium. Tectorial membrane:  a structure in the inner ear that consists of protein and collagen, originates from the spiral lamina, and rests on top of the cilia of the hair cells. Temporal bones:  the bones of the skull that overlay the temporal lobes of the brain. Temporal fossa:  a shallow depression located on the lateral aspect of the skull from which the temporalis muscle arises. Temporal lobes:  lobes of the cerebral hemispheres that are located beneath the frontal and parietal lobes and are involved in a variety of functions related to processing audition, memory, as well as receptive language. Temporomandibular joint:  the joint where the mandible articulates with the temporal bone of the skull. Temporo-parieto-occipital association area:  a region of the brain that is located at the junction of the temporal, parietal, and occipital lobes. It is involved in the integration and processing of visual, auditory, and somatosensory information, as well as in the integration of information across different sensory modalities. Tensor tympani:  a small muscle located in the middle ear that attaches to the malleus bone and plays a role in the acoustic reflex. Tensor veli palatini:  a muscle of the soft palate; responsible for the dilation and tensing of the soft palate during swallowing, speaking, and yawning. Terminal buttons:  specialized structures of an axon that are responsible for transmitting signals to other neurons. Terminal respiratory bronchioles:  the smallest branch of the bronchial tree that supplies air to the tiny sacs of air that contain the alveoli. Tertiary bronchi:  the third level of branching in the bronchial tree from the trachea. Thalamus:  a neurological relay station for all afferent pathways except for olfaction. Thoracic esophagus:  the middle third of the esophagus where the striated muscle transitions into true smooth muscle of the digestive tract. Thoracic fixation:  a squeezing together of the vocal folds, sealing off the lower respiratory tract and system during forcible expiration to increase intrathoracic pressure and rigidify the thorax for heavy lifting or biological functions such as childbirth. 450

Glossary

Thoracic vertebrae:  the 12 vertebrae below the cervical vertebrae and above the lumbar vertebrae that provide a point of attachment between the vertebral column and rib cage. Three paired cartilages of the larynx:  the arytenoid, corniculate, and cuneiform cartilages. Three unpaired cartilages of the larynx:  the thyroid, cricoid, and epiglottis as well as the intrinsic and extrinsic muscles. Threshold:  the minimum sound intensity or volume required to detect a sound. Thyroarytenoid muscle:  the body of the vocal folds. The muscle reduces the tension of the vocal folds and shortens them. Thyroepiglottic ligament:  a small fibrous band that connects the epiglottis. Thyrohyoid membrane:  suspends the larynx and is located between the hyoid bone and the superior border of the thyroid cartilage. Thyrohyoid muscle:  a small muscle located in the front of the neck that connects the thyroid cartilage of the larynx to the hyoid bone. It depresses the hyoid and elevates the thyroid gland. Thyroid cartilage:  the largest cartilage in the larynx; is located in the front of the larynx. Thyroid gland:  an endocrine gland located in the neck, just below the thyroid cartilage. Thyromuscularis:  a muscle located in the larynx that is involved in controlling the tension and position of the vocal fold during speech and singing. Tidal expiration:  the amount of air expelled from the lungs during a passive expiration. Tidal inspiration:  the amount of air pulled into the lungs during a quiet inspiration. Tidal volume:  the volume of air that is inspired and expired during a cycle of respiration. Tinnitus:  a ringing in the ears but can also be heard as a buzzing, hissing, or whistling sound. Tissue elasticity: the degree to which the fibers of the body, once deformed, are subsequently able to passively retract to their original position; a passive force of expiration. Tissues:  groups of cells that are responsible for a particular function. Tongue:  a symmetrical and muscular organ within the oral cavity that plays a significant role in speech, mastication, and swallowing. Tonotopic:  neurons that respond to high-frequency sounds are located near the base of the cochlea, while neurons that respond to low-frequency sounds are located near the apex of the cochlea. Topographic anatomy: anatomy that studies the surface of human body structures. Total lung capacity:  the amount of all air present in the lungs after a full inspiration. Trachea:  the largest passageway for air between the larynx and carina. Tragus:  a small, cartilaginous projection on the outer ear located in front of the ear canal. Transduction:  the process in which the mechanical vibrations of the basilar membrane are converted into electrochemical impulses. Transformer action:  the process through which sounds are transformed from acoustic to mechanical energy; helps to overcome the impedance mismatch that exists. Transient-evoked otoacoustic emissions (TEOAEs):  the sounds that are generated by the inner ear in response to brief, rapid changes in sound, such as clicks or tone bursts. Transtympanic (TT) needles:  medical devices that are used to deliver drugs directly into the middle ear through the tympanic membrane. These drugs are typically used for treating certain inner ear disorders such as Ménière disease. Transverse arytenoid muscles:  the paired muscles located in the larynx that connect the posterior surface of the arytenoid cartilages. Transverse/horizontal/axial/transaxial plane:  divides the body into upper and lower parts. Transverse muscles:  the muscles of the face that are oriented horizontally, or transversely, in relation to the mouth. Transverse processes:  the bony projections that project laterally from each vertebra. 451

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Transversus abdominis:  the deepest of the abdominal muscles; can compress the abdomen contributing to forced expiration. Transversus thoracis:  a thin, almost hemp leaf–shaped muscle that exists on the inside surface of the rib cage and can assist in retracting the rib cage and resisting elevation of the rib cage. Trapezius:  a large, flat muscle and is the most superficial muscle of the upper back and neck; can assist in expanding the rib cage for forced inspiration. Trapezoid body:  a structure located in the brainstem, specifically in the auditory pathway. It plays a key role in this process by ensuring that the information from both ears is relayed to the same side of the brainstem. Triangular fossa:  a small depression located on the medial wall of the middle ear. Triticeal cartilage:  a tiny nodule found in the middle thyrohyoid ligament. Tubercle of the ribs:  a small indentation located on the posterior aspect of the ribs where they articulate with the thoracic vertebrae. Tumors in the ear canal or middle ear space:  can be either benign or malignant. Tunnel of Corti:  formed by pillar cells that help to separate the inner hair cells from the outer hair cells; contains cortilymph. Tympanic membrane:  also called the eardrum; a thin, cone-shaped membrane located at the end of the ear canal that separates the outer ear from the middle ear and plays an important role in the process of hearing. Tympanic sulcus:  also called the annular sulcus; a groove or furrow in the temporal bone that surrounds the tympanic membrane located on the outer edge of the bony part of the ear canal; helps to anchor the tympanic membrane in place. Tympanogram:  a graph that displays the movement of the tympanic membrane in response to changes in air pressure. Tympanometry:  a diagnostic test that measures movement of the tympanic membrane. Tympanosclerosis:  scar tissue that forms on the tympanic membrane that is usually the result of recurrent otitis media and usually only has a minor effect on hearing. Umbo:  the deepest, most depressed part of the tympanic membrane that also radiates the cone of light. Uncrossed fibers:  the neural fibers that do not cross over from one side of the body to the other. Underbite:  when the mandibular incisors are far anterior to the maxillary incisors. Unilateral innervation:  only one side of the body is innervated with nerve fibers by the nervous system. Unpaired cartilages:  the thyroid cartilage, the cricoid cartilage, and the epiglottis. Upper esophageal sphincter (UES):  a ring of muscle located at the junction between the pharynx and esophagus that controls admittance of the bolus from the pharynx into the esophagus. Upper respiratory tract:  the part of the respiratory system that includes the nasal and oral cavities, the pharynx, and the larynx. Utricle:  connects to the membranous semicircular canals through five openings; located within the elliptical recess of the vestibule. Uvula:  the fleshy posterior terminus of the soft palate. Valleculae:  the small depressions or grooves located between the base of the tongue and the epiglottis. Valsalva maneuver:  also known as thoracic fixation; a breathing technique that involves forcibly exhaling while keeping the mouth and nose closed, resulting in increased intra-abdominal and intrathoracic pressure. Vegetative respiration:  the automatic, unconscious respiration to meet the body’s needs for the intake of oxygen and the release of carbon dioxide. 452

Glossary

Velopharyngeal incompetence:  a lack of appropriate velopharyngeal seal caused by an inability to move anatomical structures normally. Velopharyngeal insufficiency:  a lack of appropriate velopharyngeal seal due to abnormal anatomical structure. Velopharyngeal port:  the opening between the nasopharynx and the oropharynx. Velum:  a flap of muscular tissue hanging off the posterior hard palate; helps seal off the nasal cavity from the pharynx when needed. Ventilation:  the movement of air into and out of the lungs or the amount of oxygen reaching the alveoli. Ventricular system:  an interconnected series of fluid-filled cavities within the brain and also between the arachnoid mater and pia mater that functions to remove waste from the brain and deliver nutrients. Vermilion border:  the boundary between the paler skin of the face and the pinker or scarlet-colored skin of the lips. Vertebral arteries:  two large arteries that arise from the subclavian arteries and ascend through the transverse foramina of the cervical vertebrae, eventually merging to form the basilar artery at the level of the pons. Vertebral column:  the 32 or 33 individual bones known as vertebrae resting on top of each other that form the framework for the superior portion of the skeleton. Vertebral foramen:  the large opening in the center of each vertebra through which the spinal cord passes. Vertebral ribs:  floating ribs; these ribs articulate directly with the thoracic vertebrae posteriorly but have no anterior skeletal attachment. Vertebrochondral ribs:  false ribs; these ribs attach directly to the thoracic vertebrae posteriorly. Vertebrosternal ribs:  true ribs; these ribs articulate directly with the thoracic vertebrae posteriorly and the sternum in the anterior. Vertical phase difference:  the difference in timing between the opening and closing of the vocal folds during speech production. Vestibular branch:  a part of the vestibulocochlear nerve (cranial nerve VIII) that is responsible for carrying information related to the body’s balance and spatial orientation from the vestibular organs in the inner ear to the brain. Vestibular nerve:  also called the vestibular branch; one of two branches of the vestibulocochlear nerve (CN VIII) responsible for carrying sensory information related to balance, orientation, and spatial awareness from the semicircular canals and otolith organs (utricle and saccule) to the brainstem. Vestibule:  a small, oval-shaped cavity located in the bony labyrinth of the inner ear, between the semicircular canals and the cochlea. Vestibulocochlear nerve (CN VIII):  the eighth cranial nerve; responsible for transmitting sensory information related to hearing and balance from the inner ear to the brain. Vestibulo-ocular reflex:  a brainstem reflex that allows for the stabilization of visual gaze and allows a person to remain visually focused on something despite movements of the head. Vibratory cycle for the vocal folds:  one open phase and one closed phase. Vibratory motion:  a pattern that is formed from the displacement of air particles; a cycle made of compressions and rarefactions. Videofluoroscopic swallow study (VFSS):  a method of evaluating the swallow in which patients consume varying consistencies of liquids and solids mixed with barium, and the passage of the barium is viewed by fluoroscopy as it moves through the oral and pharyngeal stages of the swallow. Videokymography:  a type of digital recording technique that uses a reference line that is transverse to the glottis. Visceral pleura:  the pleural membrane that wraps and encases the lungs. 453

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Visual agnosia:  an inability to appropriately comprehend what is being visually perceived. Visual association cortex:  anterior occipital area that is responsible for processing and interpreting the afferent information received from the eyes at the primary visual cortex. Visuospatial processing:  the ability to determine the spatial relationships among objects perceived. Vital capacity:  the amount of air you can expire after a maximal inspiration. Vocal attack:  when the vocal folds are required to approximate, or adduct, and move into the stream of airflow. Vocal fold epithelium:  provides structural stability to the vocal folds and protects the underlying connective tissue from sustaining injury. Vocal fold termination:  adducting the vocal folds after sustained phonation. Vocal ligament:  also called the vocal fold; a fibrous band of tissue located in the larynx. Vocal process:  the anterior surface of the arytenoid cartilage. Vocal register:  the range of different modes of vibration of the vocal folds, which produce different qualities or timbres in the human voice. Vocal tract:  a series of cavities within the neck and head within and through which voice is produced. Vocalis muscle:  a small, delicate muscle that is part of the vocal folds in the larynx. Vomer:  a thin, unpaired triangle of bone resting medially and vertically on the floor of the posterior nasal cavity; constitutes the bony inferior posterior portion of the nasal septum. Vowel quadrilateral:  a graph of the relative position of the tongue during production of vowels. Wernicke area:  a region of the brain located at the posterior superior left temporal lobe; responsible for interpreting spoken language that is heard. Whistle register:  a fundamental frequency higher than the falsetto register and is more a product of turbulence rather than a patterned mode of vibration. White matter:  a type of tissue in the central nervous system that is made up of myelinated nerve fibers. The myelin sheath that surrounds these fibers is what gives white matter its characteristic white color. Whole-nerve action potential:  a measure of the electrical activity produced by a group of neurons in a peripheral nerve when they are stimulated. Xyphoid:  a delicate and pointed bony projection extending inferiorly from the corpus of the sternum. Zenker diverticulum:  an abnormal and acquired pouchlike structure in the hypopharynx that is related to decreased dilation of the UES due to sustained contraction of the cricopharyngeal muscle during deglutition. Zone of language:  the region of the left cerebral hemisphere that contains all the language-specific areas of the left cerebral hemisphere (Broca area, Wernicke area, arcuate fasciculus, angular gyrus). Zygomatic arch:  the junction between the zygomatic and temporal bones that form the structure of the cheekbones. Zygomatic bones:  the paired bones that make up the lateral (outer) part of the orbit (eye socket) and the prominence of the cheek. Zygomatic major:  a paired muscle of the face that courses inferiorly from the zygomatic bones to the corners of the mouth and retracts the corners of the mouth superiorly and posteriorly for smiling. Zygomatic minor:  a paired muscle of the face that courses inferiorly from the zygomatic bones; functions to elevate the upper lip and can contribute to the movements of the mouth during smiling. Zygomatic processes:  lateral bony protrusions of the maxillae that project out to articulate with zygomatic bones of the cheek.

454

Index

Note:  Page numbers in bold reference non-text material.

A

Adduction, defined, 7 Adductors, phonatory, 154 Adenosine triphosphate (ATP), 20 Adipocytes, 14 Adipose tissue, 14 Aditus, middle ear, 326 Admittance, 343 Adulthood, anatomical differences, infants and, 305–307 Aerodynamic voice, 174 parameters, 180–181 Afferent pathway, 351, 352–353 Age changes with, 305–308 respiration and, 120 Agonists, 18 defined, 7 Air alveolar, 73 conduction, 356 pressure, subglottic, phonation and, 181 Airflow convergent, 172 divergent, 172 phonation and, 181 Alternating current (AC), 349 Alveolar air, 73 ducts, 72 pressure, 112 process, 197 ridge, 236 sacs, 72 Alveoli, 48, 72–73 dental, 230 Alveolus, gas exchange at level of, 125 Alzheimer disease brain degeneration and, 398

Abdominal aponeurosis, 93–94 esophagus, 297 muscles attachment points of, 93–94 fixation, 168 transverse view of, 94 Abdominis external oblique, 94–95 transverse, 96–97 Abducens nerves, 37 Abduction, defined, 7 ABR (Auditory brainstem response), 360 Absorptive, epithelial tissue function, 11 AC (Alternating current), 349 Accessory muscles back (posterior thorax), 87–92 of inspiration, 78–92 anterior view of, 81 of neck, 84–87 of rib cage, inspiration, 78–83 Accessory nerves, 42 Acetabulum, 62 Achilles tendon, 14 ACL (Anterior cruciate ligament), 15 Acoustic parameters voice, 174 of voice, 186 reflex, 323, 343 trauma, 364 energy, 341 reflex, testing, 358–359 Acquired hearing loss, 361 Acromion process, 64 Action potentials, 21, 349 defined, 372

455

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Alzheimer disease  (continued) hippocampi and, 397 Amphiarthrodial, 25 Amplitude defined, 179, 180 peak, 347 sound, 339, 340 of vibration, 179, 180 Ampulla, 331 branch inner ear and, 326 vestibulocochlear nerve, 38 membranous, 332 Amygdala, limbic system and, 408–409 Amyotrophic lateral sclerosis, 377 Anaerobic muscles, 20 Anatomical nomenclature, 4–5 orientation, 5 terms, 5–9 variation, 2 Anatomy described, 2 specialization in, 3 Anencephaly, 376 Angle, of ribs, 59 Animal physiology, defined, 4 Annular ligament, ossicular, 323 sulcus, 319 Anotia, 341, 363 Anoxia, 48, 411, 413 described, 48 ANS (Autonomic nervous systems), 21 Antagonists, defined, 7 Anterior accessory muscles of inspiration, posterior thorax, 80–83 auricular, ligaments, 318 cerebral arteries, 414 communicating artery, 414 cruciate ligament (ACL), 15 cylindrical mass, of vertebra, 50 defined, 7 faucial pillars, 237 gap, vocal folds, 182 ligament, ossicular, 323 process, middle ear, 321 scalenes, 84, 85 semicircular canal, 331

thorax, accessory muscles of inspiration, 80–83 Antihelix, 316 Antitragus, 317 Antrum, middle ear, 326 Aortic hiatus, 77 Aperiodic, vibration, 185, 186 Apex, of cochlea, 347 Aphasia conduction, 388 Wernicke, 387 Aponeuroses, 15, 76 Appendicular skeleton, 5, 6 Applied anatomy, defined, 2 Approximal surfaces, 235 Aqueduct, cochlear, 329 Arachnoid mater, 378 Arbor vitae, 403 Arcuate fasciculus, 387 Area advantage, 342 Areolar tissue, 14 Arteries basilar, 412 cerebral anterior, 414 middle, 414 posterior, 413 common carotid, 412 communicating anterior, 414 posterior, 414 vertebral, 412 Arthritis, described, 25 Articular capsule, 25 Articulation cheeks and, 279 defined, 266 lips and, 266–268 mandible and, 276–279 pharynx and, 282 physiology of, 266–283 teeth and, 275–276 tongue and, 268 muscles and, 268–269 velum and, 279–282 Articulatory/resonance system, 27 Aryepiglottic folds, 141, 148 Arytenoids, 140 cartilages, 18 posterior view of, 135 muscles, 154

456

Index

oblique, 151 transverse, 151 Aspiration, defined, 288 Associated visual cortex, 398 Astrocytes, 373–374 Astrogliosis, 374 Atlas, 51 articulation of, 54 views of, 53 Atmospheric pressure, 112 ATP (Adenosine triphosphate), 20 Atresia, 341 Attack breathy vocal, 188 glottal vocal, 188 onset, 188 simultaneous vocal, 188 vocal, 188 Audiogram, 357 mixed hearing loss, 365 sensorineural hearing loss, 356 Audiometry, speech, 357 Audition, temporal lobes and, 396 Auditory brainstem response (ABR), 360 central nervous system, 351–354 cortex, 352, 353–355 evoked potentials, 360 meatus external, 340–341 internal, 333 mechanism auricle, 316–317 external auditory meatus, 316 outer ear, 316–321 structures of, 315 nervous system, 351–354 system, inner ear and, 327–331 tube, 325 Auricular cartilage, 316, 317 ligaments, 318 muscles, 317 extrinsic, 317–318 intrinsic, 317–318 orifice, 319 tubercle, 316 Autonomic nervous systems (ANS), 21 Autophonia, 345 Axial skeleton, 5

Axis, 51 articulation of, 54 views of, 53 Axons, 21, 370 long-range myelinated tracts, 23 myelinated, 370–371 terminals of, 371

B Baby teeth, 232 Balance eustachian tube and, 344–345 middle ear, 341–344 outer ear and, 340–341 Barium swallow modified, 302–303 Basal end, cochlea, 347 ganglia, 406–407 Parkinson’s disease and, 408 Basement membrane, 136 Basilar arteries, 412 membrane, 329, 345 Basle Nomina Anatomica (BNA), 4 Bell, Alexander Graham, 315 Bell Labs, 357 Bell palsy, 363 Bernoulli, Daniel, 180 Bernoulli effect, 170–171, 173 venturi tube effect and, 180–181 Best frequency, 350 Bicuspids, 232, 233 Bilateral innervation, 38 Biological system, defined, 1 Biology, defined, 1 Bios, defined, 1 Black lung disease, 127 Blindness, cortical, 398 Blood brain barrier, 374 oxygen level, 127, 132 hypoxia, 127 supply, to brain, 411–414 BNA (Basle Nomina Anatomica), 4 Body-cover theory, 172–173 Body systems, 9–31 cells, 9–10 joints, 24–26 organs, 27

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Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Body systems  (continued) tissues, 10–24 epithelial, 10–13 Bolus, 287–288 Bone conduction, 356 Bony labyrinth, 326 thorax, respiration and, 49–64 Brain adult, 21 Alzheimer disease degeneration, 398 blood supply to, 411–414 cerebellum, 399, 402–405 coronal section of, 372 cranial nerves and, 21 described, 375–388 hemispheres central nervous system (CNS), 393–398 cerebral, 382–387 limbic system and, 408–409 lobes of frontal, 394–395 occipital, 398 parietal, 395–396 temporal, 353, 396–398 subcortical structures, 399–402 thalamus, 405–406 ventricular system, 379–382 Brainstem, 399–402 cranial nerves and, 21 Breathing, 167 Breathy vocal attack, 188 Brevis, 89–90 Broca, Paul, 386, 387 Broca area, 386 Bronchial tree, 64, 67, 68 divisions of, 72 Brownian motion, 338 Buccal cavities, 237–238 oral preparatory stage and, 290 facial nerve branch, 38 fat pads, infants, 306 surfaces, 235 Buccinator, 214–215

Carbon dioxide poisoning, 48 Carcinoma, squamous cell, 341 Cardiac muscles, 18, 19, 20–21 semi-striated, 21 Cardiovascular system, 27 Carina, 68 Carotid arteries common, 412 internal, 412 sinus nerve, glossopharyngeal nerve, 40 Cartilage arytenoid, 18 posterior view of, 135 auricular, 316, 317 corniculate, 140 paired, 141 cricoid, 140 cuneiform, 148 larynx, 138–146 lateral view of, 140 paired, 140–141 unpaired, 141–146 thyroid, 18, 133, 134, 141 posterior view of, 135 Caudal, defined, 7 Cauliflower ear, 341 Cavum conchae, 316 Cell structures, defined, 1 Cells body of, 370 of Claudius and Boettcher, 329 Cellular physiology, defined, 4 respiration, 125 Cementum, 230 Central defined, 7 hemispheres, lobes of, 393–398 sulcus, 393 tendon, 76 Central nervous system (CNS), 23, 375–388 auditory, 351–354 connective tissue and, 13 meninges and, 21 nervous tissue, 21–24 skeletal (striated) muscles and, 20–21 Central pattern generators, 288 masticatory, 288 swallowing, 288

C Cadaver, defined, 2 Cancellous bone tissue, 16

458

Index

Cerebellar peduncles, 403, 404 Cerebellum, 399, 402–405 Cerebral arteries anterior, 414 cerebral, 414 middle ear, 414 posterior, 413 cortex, 376–377 hemisphere, 382 left, 386–387 right, 383–386 meninges, 378 Cerebrospinal fluid, 21, 380–382 shunts, 381 ventricles, 380 Cerebrum, 375 Cerumen, 318, 341 Ceruminous gland, 318 Cervical arteries, 52 esophagus, 297 vertebrae, 50 described, 51 Charcot-Marie-Tooth disease, 377 CHARGE syndrome, 282 Cheeks articulation and, 279 described, 279 oral preparatory stage and, 290 resonance and, 279 Chest, accessory muscles of, inspiration, 80–83 Chewing changes with age and, 305–308 described, 246 dysphagia and, 289 esophageal stage, disorders of, 299–302 muscles of, 246–252 oral preparatory stage, 289–291 disorders of, 290–291 structures/physiology of, 289–291 oral stage, disorders of, 291–292 pharyngeal stage, 294–295 process of, 287–291 stages of, 289 videofluoroscopic study of, 302–303 Childhood, anatomical differences, later childhood/adulthood, 305–307 Chorda tympani, middle ear, 326 Choroid plexus, 380

Chronic middle ear disease, 363 obstructive pulmonary disease (COPD), 74 Cilia, 341 Circle of Willis, 412–414 Circulatory system, 27, 29 Claudius and Boettcher, cells of, 329 Claudius Galenus, 4 Clavicle, 62 Clearing, throat, 168 Cleft palate, 198–199 Clefts, premaxillary sutures, 198 Clinical anatomy, defined, 2 Closure, vocal folds, 182–183, 184 CMs (Cochlear microphones), 349–350 CNS (Central Nervous System), 23, 375–388 auditory, 351–354 connective tissue and, 13 meninges and, 21 nervous tissue, 21–24 skeletal (striated) muscles and, 20–21 Coccygeal vertebrae, 56 Coccyx, 56 Cochlea, 327–331, 328 apex of, 347 basal end of, 347 membranous labyrinth, 332 modiolus, 38, 333 stimulation of, 345–348 transduction, 348–351 vestibular system, 331–332 osseous semicircular canals, 331–332 vestibule, 327–328 Cochlear aqueduct, 329 branch, vestibulocochlear nerve, 39 duct media, 328, 329–331 tympani, 328, 329, 345 vestibuli, 328, 329 labyrinth, osseous, 327–333 microphones (CMs), 349–350 nucleus, 352 Cochleariform process, middle ear, 325 Coding intensity, 347 Collagenous fibers, 14 Collapsed lung, 71 Collarbone, 62 Commissure of the lips, 267, 267 Common carotid arteries, 412

459

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Communicating artery, anterior, 414 Compact bone tissue, 16 Comparative anatomy, defined, 2 Compressions, sound, 338 Conduction air, 356 aphasia, 388 bone, 356 Conductive hearing loss, 362–363 Condylar, head/neck, 195 Cone of light, tympanic membrane and, 320 Congenital abnormalities, sensorineural hearing loss and, 363 hearing loss, 361 Connective tissues, 13–18 fibers, 14 muscular, 18–21 nervous, 21–24 proper, 14–15 specialized, 15–18 blood, 17–18 bone, 16–17 cartilage, 15–16 Consonants, production of, tongue and, 269 Constrictors pharyngeal, 255 middle, 257 superior, 255–257 Contralateral defined, 7 innervation, 382 Conus elasticus, 148 Convergent airflow, 172 COPD (Chronic obstructive pulmonary disease), 74 Coracoid process, 64 Corniculate cartilage, 140 paired, 141 Coronoid process, 195 Corpus, 57, 57 callosum, 23, 24, 383 of vertebra, 50 Corrugator, 224 Cortex prefrontal, 394 primary motor, 395 sensory, 396 Corti, Alfonso, 315, 329 Cortical

blindness, 398 bone tissue, 16 Cortilymph, 329 Costal groove, of rib, 59 Costochondritis, 15 Costovertebral joints, 59 Cotton swabs, 340 Cotugno, Domenico, 315 Coughing, throat, 168 Coupling theory, nonlinear source-filter, 173 Cranial nerves, 21, 32–43 abducens nerves, 37 accessory, 42 facial nerves, 37–38 glossopharyngeal nerve, 39–40 hypoglossal, 42–43 mnemonic, 33 oculomotor nerve, 36 olfactory nerve, 33–34 optic nerve, 34–36 origin, type, function, 34 trigeminal nerve, 36–37 trochlear nerve, 36 vagus, 40–42, 139 branches of, 138 vestibulocochlear nerve, 38–39 Cri du chat, 196 Cricoarytenoid muscles lateral, 154–155 posterior, 155 Cricoid cartilage, 15, 16, 140, 143 Cricoidectomy, 145 Cricopharyngeal muscle, 258–259 Cricopharyngeus muscle, 258–259 Cricothyroid joints, 141, 144 ligament, 15, 148 lateral, 148 middle, 148 muscle, 138, 143, 151, 152, 155 lateral, 152–153 Cricotracheal membrane, 147 Crista ampularis, 331 Crista ampullaris, 354 Crossed fibers, 353 Crown, tooth, 230 Crura antihelicis, 316 stapes, 323 Cuboidal tissue, 13 Cuneiform cartilages, 148 460

Index

Cupid’s bow, 267, 267 Cupola, 331 Curved membrane buckling, 342 Cuspids, 232 Cuticular layer, tympanic membrane and, 320 Cymba conchae, 316 Cytology, defined, 2 Cytoplasm, defined, 9 Cytoskeleton, defined, 9

labii inferioris, 221, 222 Depressors facial muscles and, 212, 221–224 velum, 254–255 Descriptive anatomy, defined, 2 Developmental anatomy, defined, 2 Diaphragm, 76 views of, 76 anteroposterior, 77 inferior, 77 Diarthrodial/synovial joints, 25 Diffusion, 126 Digastric muscles, 18, 156–157 Digastricus, 250 Digestive system, 27, 30 Digital videoendoscopy, 185 Diphthongs defined, 273 in English, 274 production of vowels and, 273–274 Direct current (DC), 349 Discharge rates, 350 Distal, defined, 7 Distortion product emissions (DPOAEs), 360 Divergent airflow, 172 Dorsal defined, 7 midbrain, 353 posterior (back), 7 Down syndrome, 279, 282 DPOAEs emissions (Distortion product), 360 Ductus reuniens, inner ear, 332 Dura mater, 378, 379 Dysphagia, 289

D Darwin, Charles, facial expression and, 211 Darwin tubercle, 316 dB (Decibel), defined, 179, 180 DC (Direct current), 349 de Boulogne, Duchenne, facial expression and, 211 Decibel (dB), defined, 179, 180 Deciduous teeth, 232, 233 Deep, defined, 7 Deglutition changes with age and, 305–308 coordination of, with respiration, 309 dysphagia and, 289 esophageal stage, disorders of, 299–302 infants, physiology of, 307 oral preparatory stage, 289 disorders of, 290–291 structures/physiology of, 289–291 pharyngeal stage, 294–295 process of, 287–291 stages of, 289 videofluoroscopic study of, 302–303 Deiters, Otto, 330 Deiters cells, 330 Demyelinating illnesses, 377 Dendrites, 370 Dense connective tissue, 14 irregular tissue, 15 regular tissue, 14 Dental alveoli, 230 arches, 230, 231 surfaces, 234–235 Dentition, mixed stage, 234 Deoxygenated blood, 73 Depolarization, 349 Depolarized, hair cell, 349 Depressor anguli oris, 222, 223

E EAM (External auditory meatus), 316, 318–319, 340 Ear anatomy of, 18 canal impacted, 363 tumors in, 363 Eardrum, 319–321 branch, glossopharyngeal nerve, 40 perforated, 321 Earflap, 317 Earlobe, 317 Earwax, 318, 341 ECochG (Electrocochleography), 360–361 461

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

ECOG (Electrocochleography), 360–361 Ecto, defined, 7 Edison, Thomas, 315 EEG (Electroencephalography), described, 4 Efferent pathway, 353 Ekman, Paul, facial expression and, 211 Elastic cartilage, 15 fibers, 14 Elasticity of voice, 174 Electrocochleography (ECOG or ECochG), 360–361 Electroencephalography (EEG), described, 4 Elevators facial muscles and, 212 of velum, 253–254 Elvis muscle, 218 Embryology, defined, 2 Enamel, 230 End feet, of astrocytes, 374 Endo, defined, 7 Endocochlear potential (EP), 349 Endocrine system, 27, 29 Endolymph, 329 Endolymphatic duct, inner ear, 332 Endomysium, 20 Endoplasmic reticulum, defined, 9 Enhancement, selective sound, 340 Enteric nervous system, 21 EP (Endocochlear potential), 349 Epicranius, 224 Epiglottis, 15, 16, 145, 146, 239 pharyngeal stage, 294 Epimysium, 20 Epithelial tissues, 10–13 functions of, 11 types of, 13 Epithelium, vocal folds, 136 Epitympanic recess, middle ear, 321 ERV (Expiratory reserve volume), 118–119 Erythrocytes, 18 Esophageal hiatus, 77 motility disorder, 300 peristalsis, 299 phase, mastication/deglutition, 289 rings/webs, 301 sphincter lower, 299 upper, 297

stage described, 297–302 disorders, 299–302 structures/physiology of, 299 Esophagitis, 302 Esophagus, 239, 297 Ethmoid, 204–205 Eustachi, Bartolomeo, 327, 344 Eustachian tube, 324, 325 hearing/balance and, 344–345 Excretory system, 27 Expiration auditory meatus, 316, 318–319, 340 defined, 48 forced, physics of, 113–117 muscles of, 92–102 accessory muscles of, 98–102 primary, 92–98 passive, 75 patterns of, 108 primary muscles of, 93 tidal, 114 Expiratory reserve volume (ERV), 118 Extension, defined, 7 External auditory meatus (EAM), 316, 318–319, 340–341 auricular, orifice, 319 defined, 7 intercostals, 78–80 oblique abdominis, 94–95 otitis, 341 Extracellular fluid, defined, 9 Extrinsic auricular ligaments, 318 muscles, 317–318 defined, 7 laryngeal membranes/ligaments, 146–147 muscles intrinsic, 239–241 of larynx, 155–163 tongue, 241–245

F Face bones of, 194–204, 206 cleft palate, 198–199 hard palate, 196–197

462

Index

inferior nasal conchae, 201–203 lacrimal, 203, 204 mandible, 194–206 maxillae, 196–197 nasal, 200, 201 palatine, 201 vomer, 203 zygomatic, 200 muscles of, 210–239 buccinator, 214–215 depressor anguli oris, 222 depressor labii inferioris, 222 depressors, 212, 221–224 elevators, 212, 217–221 levator anguli oris, 220–221 levator labii superioris, 217 levator labii superioris alaeque nasi, 217–218 mentalis, 223, 224 nerves, 37–38 orbicularis oris, 212, 213 parallel muscles, 212, 224 risorius, 215, 216 transverse, 212, 214–216 zygomatic minor, 219–220 Facial Action Coding System (FACS), 211 Facial expressions Charles Darwin and, 211 Duchenne de Boulogne and, 211 Margaret Mead and, 211 Paul Ekman and, 211 supplementary muscles of, 224–226 FACS (Facial Action Coding System), 211 Fahlman, Scott, 222 False vocal folds, 138 Falsetto register, 188 Fascia, 14, 20 Fascicles, 19 Fasciculi, 20 Fast-twitch oxidative fibers, 20 Faucial pillars anterior, 237 posterior, 237 Federative Committee on Anatomical Terminology, 4–5 FEES (Fiberoptic endoscopic evaluation of swallow), 303–304 Femur, 16 Fernel, Jean, term physiology introduced by, 4 Fiberoptic endoscopic evaluation of swallow (FEES), 303–304

Fibers, crossed/uncrossed, 353 Fibroblasts, 14 Fibrocartilage, 16, 49 Fibrous cartilage, 16 layer, submucous, 239 Figurative language, 384 Fissures, of brain, 378 Fixators, 18 Flexion, defined, 7 Footplate, stapes, 323 Foramen of Monro, 380 vena cava, 77 Forced expiration, 75 inspiration, 75 physics of, 113–117 respiration, 75, 109 physics of, 113–117 Fossa scaphoid, 316 triangularis, 316 FRC (Functional residual capacity), 119 Frequency best, 350 coding, 347 defined, 174 sound, 339, 339 Frontal coronal plane, 7 process, 197 Frowning, muscles associated with, 222 Functional residual capacity (FRC), 119 Fundamental frequency, of voice, 174–179

G Gag reflex, 402 Galenus, Claudius, 4 Ganglion, spiral, 333 Gas exchange, 72–73 Alveolus and, 125 General anatomy, defined, 2 Geniculate body, medial, 352 Genioglossus, 242–244 Geniohyoid, 250–251 muscles, 18, 157–158 Gingiva, 230 Gingival line, 230

463

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Glandular tissue, 13 Glenoid fossa, 64 Glial cells, 21, 370, 372–374 scars, 374 Glossopharyngeal nerve, 39–40 Glottal fry, 187 vocal attack, 188 Glottis, 133 cartilage, posterior view of, 135 posterior view of, 134 posterior view of, 135 Glutamate, neurotransmitter, 349 Glycolytic fibers, 20 Goblet cells, 68 Golgi apparatus, defined, 9 Gomphosis, 25 Gray matter, 21, 371, 372 cortex and, 377 Gray’s Anatomy, 5 Greater horns, hyoid bone, 137, 138 Gross anatomy, defined, 2 Ground substance, 14 Guillain-Barré disease, 377 Gum line, 230 Gums, 230 Gustatory system, 308 Gyri, 377, 378

Helicotrema, 329 Helix, 316 Hemiparesis, 400 Hemiplegia, 400 Hemispheres central, 393–398 cerebral, 382–387 Hemorrhagic vocal polyp, 176, 178 Hensen, Victor, 330 Hensen cells, 330 Herpes, 363 Heschl gyrus, 353 High ankle sprain, 25 frequency sounds, 347 resolution manometry (HRM), 304–305 speed digital videoendoscopy, 185 Hippocampi, 396–397 Hippocampus, limbic system and, 408 Hippocrates, 4 Histology, defined, 2 Hooke, Robert, 9 Horizontal, semicircular canal, 331–332 Hourglass shape, vocal folds, 182–183 HRM (High-resolution manometry), 304–305 Hyaline (gaslike) cartilage, 15 Hydrocephalus, 381 Hyoepiglottic, ligament, 145, 147 Hyoglossus, 244 Hyoid bone, 136–138 anterior view, 137 body, 138 infants, 306 Hyolaryngeal excursion, 168 Hypercapnia, 48 Hyperpolarization, 349 Hypoglossal nerve, 42–43 Hypokinetic dysarthria, 408 Hypopharynx, 239 Hypoplasia, mandibular, 196 Hypothalamus, limbic system and, 408, 409 Hypoxia, 132, 411, 413 blood oxygen level, 127 described, 48

H Habenula perforata, 328 Habitual pitch, 177, 179 Hair cells, 347, 348 Handle, middle ear, 322 Hard palate, 236 anatomy of, 197–199 Head of rib, 58 Hearing conduction, air/bone, 356 eustachian tube and, 344–345 middle ear, 341–344 outer ear and, 340–341 loss conductive, 362–363 mixed, 364, 365 sensorineural, 363–364 types of, 361–365 Heel cord, 14 Helical crura, 316

I IC (Inspiratory capacity), 119 IFAA (International Federation of Associations of Anatomists), 4 Ilium, 62 464

Index

Illness, sensorineural hearing loss and, 363 Immittance meter, 358 Immobile articulators, 266 Immune system, 27 Impacted ear canal, 363 Impedance, 342 Incisivus labii inferior, 224 superior, 224 Incisors overjet, 235 tooth, 232 Incudomalleolar joint incus, 322 middle ear, 321 Incudostapedial joint, 323 stapes, 322 Incus, 322–323 Inertia, of voice, 174 Inertial properties, sound, 339 Infants deglutition, physiology of, 307 oral cavity of, 306 Inferior cerebellar peduncles, 403 colliculus, 353 defined, 7 longitudinal muscle, 240–241 nasal conchae, 201–203 pharyngeal constrictor muscle, 141 superior, 255–257 wall, middle ear, 326 Infra, defined, 7 Infrahyoid, muscle, 159 Inner ear, 326–333 auditory system, 327–331 cochlea, 326–333 osseous spiral lamina, 328 physiology of, 345–351 vestibulocochlear nerve, 332–333 hair cells (IHC), 329, 347 Innermost intercostals, 100, 101 Inspiration accessory muscles of, 78–92 anterior view of, 81 accessory muscles of rib cage, inspiration, 78–83 defined, 48 forced, physics of, 113–117 muscles of, 76–78 tidal, 114

Inspiratory capacity (IC), 119 checking, 111 reserve volume (IRV), 118 Insufficiency, velopharyngeal, 282, 283 Insula, 353 Integumentary system, 27 Intensity changes, vocal folds movement and, 180 coding, 347 sound, 179–180 Interarytenoid muscle, 150, 154 Intercostals, 78–79 innermost, 100, 101 internal, 98 Intermaxillary sutures, 197, 198 Intermediate (fibrous) layer, tympanic membrane and, 320 Internal auditory meatus, 333 carotid arteries, 412 defined, 7 intercostals, 78–79, 98 chondral portion of, 80 oblique abdominis, 95–96 International Anatomical Nomenclature Committee, 4 International Federation of Associations of Anatomists (IFAA), 4 Interneurons, 370 Intervertebral discs, 50 foramina, 50 Intonation, phonation and, 189 Intracellular fluid, defined, 9 Intraoral pressure, 113 Intrapleural pressure, 112–113 space, 70 Intraventricular shunt, 381 Intrinsic auricular ligaments, 318 muscles, 317–318 defined, 7 laryngeal membranes, 147–149 tongue muscles, 239–241 Ipsilateral, defined, 7 IRV (Inspiratory reserve volume), 118 Ischial tuberosity, 62 Ischium, 62 465

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Isthmus, 319 middle ear, 325

unpaired, 141–146 muscles of, 149–163 extrinsic, 150, 155–163 infrahyoid, 159 intrinsic, 149, 150–155 Latency, 350 intensity function, 350 Lateral cricoarytenoid ligament, 148 muscles, 143–144, 154–155 defined, 7 lemniscus, 353 ligament, ossicular, 323 process, middle ear, 321 pterygoid, 249 semicircular canal, 331–332 middle ear, 324 sulcus, 393 thyrohyoid ligament, 147 ventricles, 380 wall, middle ear, 321 Latissimus dorsi, 91 Laughter yoga, 216 Left-handed individuals, 383 Lenticular process, incus, 322 Leptomeninges, 378 Lesion localization, 386 Lesser horns, hyoid bone, 137, 138 Leukocytes, 14, 18 Levator, 217 anguli oris, 220–221 costarum, 89–90 labii superioris alaeque nasi, 217–218 facial muscles and, 217–221 levator labii superioris, alaeque nasi, 217–218 veli palatini, 253 Lewy bodies, 408 Ligaments, 14 auricular, 318 cricothyroid, 15, 148 lateral, 148 middle, 148 hyoepiglottic, 145, 147 lateral ossicular, 323 thyrohyoid, 147 median cricothyroid, 144 middle thyrohyoid, 147

J Jakob, Matthias, 9 Jitter, 186 Joints, 24–26 cricothyroid, 144 defined, 1 diarthrodial, 25 functional classification (movement) of, 25 incudomalleolar joint, 322 incudostapedial, stapes, 322 synarthrodial, 25 Jugular view, middle ear and, 326

K Kabuki syndrome, 282 Kataria, Madan, 216 Kinocilium, 331, 348

L Labial seal, infants, 306 surface, 235 Labyrinth, membrane, 332 Labyrinthian middle ear, 324 wall, middle ear and, 324 Labyrinthine, 326–333 Lamina osseous spiral, 328 propria, 136 superficial, 136 Laminae, of vertebra, 50 Laryngeal, membranes, 146–147 nerve, superior external branch of, 138 internal branch of, 138 Laryngopharynx, 239 Laryngoscope, 147 Laryngostroboscopy, 185 Larynx, 66, 67, 133, 138–163 biological functions of, 167–170 cartilages of, 138–146 lateral view of, 140 paired, 140–141

466

Index

posterior, ossicular, 323 spiral, 329 superior, ossicular, 323 thyroepiglottic, 145 vocal, superior view, 137 Limbic system, 408–409 Limbus, spiral, 330 Linea alba, 94 semilunaris, 94 Lingual acquired weakness, 274–275 branch, glossopharyngeal nerve, 40 septum, 239 surfaces, 234 Lips, 212 anatomy of, 267 articulation and, 266–268 commissure of, 267 oral preparatory stage and, 289 Lobes frontal, 394–395 parietal, 395–396 Lobule, 317 Long process, incus, 322 Longis, 89–90 scapulae, 90–91 Longitudinal muscle inferior, 240–241 superior, 239–240 pharynx muscles, 259–261 section, 7 Long-range myelinated axon tracts, 23 Loose connective tissue, 14 Lou Gehrig’s disease, 377 Loudness, defined, 179, 180 Low-frequency sounds, 347 Lower esophageal sphincter, 299 respiratory tract, 64, 65 Lumbar vertebrae, 54–55 anatomy of, 55 Lumbodorsal fascia, 94 Lungs, 69–72 black lung disease, 127–128 cadaver, 69 lobes of, 69–70 pleural membranes of, 70–71 volumes/capacities of, 117–119

measuring, 122–124 Lymphatic system, 27 Lysosomes, defined, 9

M Macrophages, 14 Macroscopic anatomy, 2 Macrostructure processing, 385 Macula, inner ear, 332 Macule, 354, 355 Malleolar folds, tympanic membrane and, 320 prominence, middle ear, 322 stria, middle ear, 322 Malleus, 321–322 Malocclusions, 235, 235 Mamillary bodies, limbic system and, 408, 409 Mandible, 194–196 angle of, 195 articulation and, 276–279 body of, 195 branch, trigeminal nerve, 37 described, 276 infants, 306 oral preparatory stage and, 289–290 ramus of, 230 weakness of, 278 Mandibular developmental disorders of, 196 hypoplasia, 196 symphysis, 26 Manometry, 121–122 Hixon’s water glass, 122 Manubrium middle ear, 321, 322 sterni, 56 Marconi, Guglielmo, 315 Marfan syndrome, 13–14, 196 Masseter, 246–247 Mast cells, 14 Mastication changes with age and, 305–308 described, 246 dysphagia and, 289 esophageal stage, disorders of, 299–302 muscles of, 246–252 oral preparatory stage, 289–291 disorders of, 290–291 structures/physiology of, 289–291

467

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Mastication  (continued) oral stage, disorders of, 291–292 pharyngeal stage, 294–295 process of, 287–291 stages of, 289 videofluoroscopic study of, 302–303 Masticatory central pattern generator, 288 Matrix, connective tissue, 13 Maxillae, 196–197 Maxillary branch, trigeminal nerve, 37 MBSS (Modified barium swallow study), 302–303 Mead, Margaret, facial expression and, 211 Mechanical energy, 341 Media, scala, 328 Medial defined, 7 geniculate body, 352 pterygoid, 247–248 wall, middle ear, 324 Median cricothyroid ligament, 144 plane, 7 Medulla, 399–400 decussation of motor neurons at, 401 Membrane ampulla, 332 basilar, 329, 345 cricotracheal, 147 curved, buckling, 342 labyrinth, 332 laryngeal, 146–147 intrinsic, 147–149 ligament, 146–147 quadrangular, 148 Reissner, 329, 345 reticular, 330 semicircular canal, 332 tectorial, 330, 347 thyrohyoid, 142, 147 tympanic, 319–321 Membranous labyrinth, 326 Meninges central, 378 CNS (Central Nervous System) and, 21 connective tissue, 13 Meningitis, 363, 378 Mental protuberance, 194 symphysis, 194 tubercles, 195

Mentalis, 223, 224 Mesothelium, 70 Microbial, physiology, defined, 4 Microglia, 374 Micrognathia., 196 Microscopic anatomy, defined, 2 Midbrain, 399 Middle cerebellar peduncles, 403 cerebral arteries, 414 cricothyroid ligament, 148 pharyngeal constrictor muscle, 258 scalenes, 85 Middle ear, 321–326 cavity anterior wall, 325 floor, 326 medial wall, 325 posterior wall, 326 superior wall, 326 chronic disease of, 363 incus, 322–323 infections of, 324, 344 malleus, 321–322 medial wall, 324 muscles of, 324 ossicles, 321 ossicular ligaments, 323 physiology of, 341–344 stapes, 323 tumors in, 363 Midsagittal plane, 7 Milk teeth, 232 Mitochondria, 20 defined, 9 Mixed dentition stage, 234 Mobile articulators, 266 Modal register, 187 Modified barium swallow study (MBSS), 302–303 Modiolus, 350 cochlea, 333 Molars, 232, 233 Monoloud voice, 189 Monophthong, 273 Monopitch voice, 189 Morbid anatomy, defined, 2 Motor branch, glossopharyngeal nerve, 40 homunculus, 395 nerves, 21

468

Index

neurons, 370 decussation of at medulla, 401 unit described, 18 MS, 377 Mucosal wave, 171 movement of, 184–185 Mucous layer, tympanic membrane and, 320 Multiple sclerosis (MS), 23–24, 377 Muscles accessory back (posterior thorax), 87–92 of inspiration, 78–92 of neck, 84–87 of rib cage, inspiration, 78–83 arytenoids, 154 auricular, 317–318 cells, 20 cricothyroid, 138, 143, 151, 152, 155 lateral, 152–153 posterior, 153–155 muscles, lateral, 154–155 digastric, 18, 156–157 elevation, pharyngeal stage, 294 fibers, 19 geniohyoid, 18, 157–158 inferior pharyngeal constrictor, 142 infrahyoid, 159 interarytenoid, 150, 154 of larynx, 149–163 extrinsic, 150, 155–163 intrinsic, 150–155 lateral cricoid, 144 of middle ear, 324 mylohyoid, 18, 158 omohyoid, 160 posterior cricoid, 144 respiratory, 155 stapedius, 323 sternothyroid, 162 stylohyoid, 18 thyroarytenoid, 153, 155 thyrohyoid, 142, 161, 162 tongue, 239–245 intrinsic, 239–241 transverse, 241 types of, 20 of velum, 252–255 Muscular process, 140 system, 27, 31

tissues, 18–21 Musculus uvulae, 253–254 Myelin, 21, 370 Schwann cells and, 373 Myelinated axons, 21, 370–371 Mylohyoid, 250 muscles, 18, 158 Myoelastic-aerodynamic theory, 170–171, 172 Myofibrils, 20 Myoglobin, 20 Myosin, 20 Myringotomy tubes, 344 insertion of, 345

N Nares, 238 Nasal cavity, 64, 238 described, 279 choanae, 64 Nasopharynx, 238 Neck of rib, 58 stapes, 322 of tooth, 231 Nerves accessory, 42 phrenic, 415 spinal, 414–415 Nervous system, 22, 27, 31 cells of, 369–375 peripheral, 414–416 tissues, 21–24 Neuroglia, 370, 372–374, 372 Neurons, 21, 23, 369–372 Neurotransmitters, 21 glutamate, 349 Noise-induced hearing loss, 330 Nomina Anatomica, 4 Nonspeech (Biologic functions), 168 abdominal fixation, 168 breathing, 167 thoracic fixation, 168 Nucleus, defined, 9

O OAEs (Otoacoustic emissions), 349, 359–360 Oblique, abdominis, external, 94–95

469

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Occipital bone, 208, 209 lobes of, 398 Occlusal surface, 234 Occlusion, teeth, types of, 235–236 Oculomotor nerve, 36 Offset, vocal folds, 188 OHCs (Outer hair cells), 347 Olfactory nerve, 33–34 Oligodendrocytes, 21, 373 Omohyoid muscle, 160 Onset attack, 188 Ophthalmic branch, trigeminal nerve, 36 Optic chiasm, 34–35 nerve, 34–36 tract, 35 Optimal pitch, 176, 179 Oral cavity, 66, 226–237 anatomical boundaries of, 226 infants, 306 structures of, 227–237 dentition, 230–237 saliva glands, 230 stage, mastication/deglutition, disorders of, 291–292 state, mastication/deglutition, 289 tongue, 227–229 Oral preparatory stage deglutition and, 289 disorders of, 290–291 mastication/deglutition, 289 structures/physiology of, 289–291 Orbicularis oculi, 224 oris, 212, 213, 267 Organ of Corti, 329, 330, 347 Organelles, 9 Organs, 27–31 defined, 1 Oropharynx, 238 Osseous cochlear labyrinth, 327–333 semicircular canals, 306, 331–332 spiral lamina, 328 Ossicles, middle ear, 321 Ossicular Chain, 321 movement of, 341–344 traumatic discontinuity, 342

ligaments, 323 Osteoarthritis, described, 25 Osteoblasts, 16 Osteogenesis imperfecta, 14 Osteoma, 341 Otitis external, 341 media, 324, 344, 363 Otoacoustic emissions (OAEs), 349, 359–360 Otolithic membrane, inner ear, 332 Otoliths, inner ear, 332 Otosclerosis, 323, 363 Otoscope, 355 Ototoxic drugs, sensorineural hearing loss and, 363 Outer ear, 316–321 auditory meatus external, 318–319 tympanic membrane, 319–321 auricle, 316–317 auricular cartilage, 317 ligaments, 318 muscles, 317–318 physiology of, 340–341 Outer hair cells (OHCs), 329, 347 Oval window cochlea, 329 middle ear, 324 vestibule, 328 Overjet, maxillary incisors and, 235 Oxygen, blood and, 411

P Paired cartilages, 140–141 cricoid, 140 Palatal aponeurosis, 252 rugae, 236 Palatine bones, 201 process, 197 Palatoglossus, 244–245 Palatopharyngeus, 255, 259–260 Parallel muscles, of face, 212 Parasagittal plane, 7 Parasympathetic nervous system, 21 Parietal bones, 206–207 lobes, 395–396

470

Index

pleura, 70 Parkinson, James, 408 Parkinson’s disease, basal ganglia and, 408 Parotid glands, 230 Pars flaccida, tympanic membrane and, 320 tensa, tympanic membrane and, 320 Passive expiration, 75 Pathological anatomy, defined, 2 Peak amplitude, 347 Pectoral girdle, 62, 63 Pectoralis major, 80–81 minor, 81–82 Pedicles, of vertebra, 50 Peduncles, 403 Pelvic girdle, 61–62 Penetration, defined, 288 Perforated eardrum, 321 tympanic membrane, 363 Perfusion, 126 Perilymph, 329 Perilymphatic space, 329 Perimysium, 20 Period of vibration, 185 Periodicity vibration, 185–186 Periosteum, 16 Peripheral, defined, 7 Peripheral nervous system (PNS), 21, 23, 375, 414–416 Peristalsis, esophageal, 299 Permanent teeth, 232, 234 Peroxisomes, defined, 9 Perturbation, 186 Phalangeal cells, 330 Pharyngeal branch, glossopharyngeal nerve, 40 constrictors, 255 inferior, 258 middle, 257 pharyngeal stage and, 294–295 superior, 255–257 elevation, tongue and, 294 plexus, vagus nerve, 40–41 stage described, 297–302 disorders of, 295–297 mastication/deglutition, 289, 293–294 stasis, 296

Pharyngotympanic tube, 325 Pharynx, 66, 238–239 articulation and, 282 longitudinal muscles of, 259–261 muscles of, 255–261 Philtral pillars, 267 Philtrum, 267, 267 Phonation, 133, 168–169 aerodynamic principles of, 180–181 airflow and, 181 Bernoulli effect, 180–181 linguistic aspects of, 188–189 nonlinear source-filter coupling theory, 173 parameters of, 173–181 acoustic, 174–179 amplitude, 179–180 intensity, 179–180 sustained, 188 theories of, 170–173 threshold pressure, 171 venturi tube effect and, 180–181 vocal folds, closure, 182–183, 184 Phonatory adductors, 154 system, 27 Phrenic nerve, 77, 415 Physiology described, 4 divisions of, 4 Pia mater, 378 Pierre Robin sequence, 282 Pillar cells, 329 Pinna, 316, 340–341 anatomy of, 317 Pitch change mechanisms, 176 defined, 178 habitual, 177, 179 optimal, 176, 179 range, 178 sound, 340 Pituitary gland, limbic system and, 409 Plant, physiology, defined, 4 Plasma membrane, defined, 9 Platysma, 224, 225, 251 Pleurae, 70, 71 Pleural membranes, of lungs, 70–71 Pleurisy, 71 Pneumoconiosis, 127–128 Pneumothorax, 71

471

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

PNS (Peripheral nervous system), 21, 23, 375, 414–416 Pons, 399–400 Posterior auricular, ligaments, 318 cerebral arteries, 413 communicating artery, 414 cricoarytenoid muscle, 153–155 defined, 7 faucial pillars, 237 gap, vocal folds, 182 inferior serratus, 98–99 ligament, ossicular, 323 quadrate lamina, 143 scalenes, 86 semicircular canal, 331 serratus superior, 87, 89 thorax, accessory muscles of, 87–92 Postlingual hearing loss, 361 Practical anatomy, defined, 2 Preauricular tags, 341 Prefrontal cortex, 394 Premaxillary sutures, 197 clefts of, 198 Presbycusis, 333 sensorineural hearing loss and, 363 Presbyphagia, 307–308 Pressure, subglottic, 181 Primary, 395–396 bronchi, 68 angles of, 68 cortex auditory, 397 motor, 395 sensory, 396 visual, 398 Prime movers, 18 Procerus, 224 Promontory, middle ear, 324 Prone, defined, 7 Prosody, 189, 384 Prosopagnosia, 384–385 Protective epithelial tissue function, 11 redundancy, 38 Protraction, defined, 7 Proximal, defined, 7 Pterygoid lateral, 249 medial, 247–248

Pterygomandibular raphe/ligament, 214–215 Pubic bone, 62 symphysis, 62 Pulmonary arteries, 73 veins, 73 Pulp, tooth, 231 Pulse register, 187 Pure tone audiometry, 356 Pyramidal decussation, 400, 401 eminence, middle ear, 326 Pyriform sinuses, 145, 148

Q Quadrangular membrane, 148 Quadratus lumborum, 100, 102 Quadrilateral, vowels, 272–273 Quiet inspiration, 75 respiration, 75, 108–110, 116–118

R Radiological anatomy, defined, 2 Rami, 195 Ramus, of mandible, 230 Rarefactions, sound, 338, 339 Rectangular membrane, 330 Rectus abdominis, 94, 97, 98 Recurrent laryngeal nerve (RLN), 138 vagus nerve, 42 Red blood cells, 17 Reflex acoustic, 323, 343 defined, 401–402 gag, 402 vestibulo-ocular, 402 Regional anatomy, defined, 2 Register falsetto, 188 modal, 187 pulse, 187 vocal, 186–187 whistle, 188 Regularity vibration, 185–186 Reinke edema, 176, 178, 179 Reissner, Ernst, 315

472

Index

Reissner membrane, 329, 345 Reproductive system, 27 Residual volume (RV), 119 Resistive breathing device, 124 Resonance cheeks and, 279 defined, 266, 270 frequency, 270 velum and, 279–282 Resonant frequency, 340 Resonators, 169 Respiration advanced age and, 120 categorization of muscles of, 75–76 coordination of, with deglutition, 309 cycle of, 108 described, 47–49, 107 forced, 109 forces of active, 111 passive, 111–112 instrumentation, 120–124 measurement of, 120–124 pressure, 121–122 rate, 121 movement of rib cage during, 60–61, 62 muscles of, 74–102 muscular use patterns in, 75 physics of, 113–117 pressures involved in, 112–113 quiet, 108–110, 116–118 skeletal framework for, 49–64 bony thorax, 49–64 vegetative, 108 Respiratory capacities, 118 center, 109 muscles, 155 passages, 64 system, 27, 30 muscles of, 154 tissues, 72–73 weakness, therapy for, 124 zones, 72 Resting potentials, 349 Reticular activating system, 401 connective tissue, 14 fibers, 14 Retraction, defined, 7

Rheumatoid arthritis, 14 Rib cage, 57, 58–61 accessory muscles of, inspiration, 78–83 movement of during respiration, 60–61, 62 Ribosomes, defined, 9 Ribs anatomy of, 58–59 articulation of, superior view, 60 attachments between, 59 head of, 58 Right-handed individuals, 383 Risorius, 215, 216 RLN (Recurrent laryngeal nerve), 138 vagus nerve, 42 Roof, middle ear, 326 Root, tooth, 230, 231 Rostral, defined, 7 Round window, 344 cochlea, 329 middle ear, 324 Rubella, sensorineural hearing loss and, 363 RV (Residual volume), 119

S Saccule branch inner ear, 332 vestibulocochlear nerve, 39 Sacral vertebrae, 55–56 Sacrum, view of, 55 Sagittal/vertical plane, described, 7 Saliva, 230 glands, 230 Salivary glands, oral preparatory stage and, 290 Salpingopharyngeus, 259–260 Scala media, 328, 329–331 tympani, 328, 329, 345 vestibuli, 328, 329 Scalenes, 84 Scaphoid fossa, 316 Scapula, 63–64 posterior view of, 63 spinous process of, 64 Scarpa ganglion, 38 Schatzki ring, 302 Schindylesis, 25 Schleiden, Matthias Jakob, 9 Schwann, Theodor, 9 Schwann cells, 21, 373

473

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Sebaceous gland, 318 Secondary bronchi, 68 tympanic membrane, 324 Secretory tissue, 13 Selective enhancement, sound, 340 Semicircular canals membranous, 332 osseous, 326, 331–332 Semilunar notch, 195 Sensorineural hearing loss (SNHL), 363–364 Sensory (afferent) nerves, 21 homunculus, 396 nerves, 11 neurons, 370 Serratus anterior, 82–83 posterior inferior, 98–99 superior, 87, 89 Shaft, of rib, 58 Shearing action, sound waves, 347 Shimmer, 186 Short process, incus, 322 Simultaneous vocal attack, 188 Sinuses, pyriform, 145 Skeletal (striated) muscles, 18–19 system, 27, 28 Skull bones of, 204–210 ethmoid, 204–205 facial, 206 occipital, 208, 209 parietal bones, 206–207 sphenoid, 209, 210 temporal, 207–208 suture/seam of, 25 SLN (Superior laryngeal nerve) branch of external, 138 internal, 138 vagus nerve, 42 Smiling, muscles associated with, 216 Smooth muscles, 18, 19 nonstriated, 20–21 Snarling, muscles associated with, 218 SNHL (Sensorineural hearing loss), 363–364 SOC (Superior olivary complex), 352 Soft palate. See Velum

Soma, 370 Somatic nervous system, 21 Somatosensation, 395–396 Sound high-frequency, 347 intensity, 179–180 transduction, structures involved in, 346 low-frequency, 347 properties of, 338–340 waves, pinna and, 345 Source-filter theory of vowel production, 271–272 Speech audiometry, 357 breathing, vegetative respiration and, 110 perception, 353 reception threshold, 357–358 Sphenoid, 209, 210 Spikes (action potentials), 350 rate, 350 Spinal cord, 21, 410–411 spinal nerves and, 21 nerves, 414–415 spinal cord and, 21 Spindle shape, vocal folds, 183 Spinous process, 50, 60 of the scapula, 64 Spiral ganglion, 333 ligament, 329 limbus, 330 organ, 329 Spirometry, 122 Spongy bone tissue, 16 Squamous cell carcinoma, 341 epithelium, superficial layer of, 136 tissue, 13 Standard anatomical position, 5 Stapedius muscle, 323 Stapes, 16, 17 Stenosis, 363 Stereocilia, 330, 347, 348 Sternoclavicular joints, 62, 63 Sternocleidomastoid, 86–87 Sternohyoid muscle, 161–162 Sternothyroid muscle, 162 anterior view, 163 Sternum, 56–57 attachments between, 59 Stiffness, of voice, 174 474

Index

Stimulation, cochlea, 345–348 Stress, phonation and, 189 Stria vascularis, 329, 349 Striated muscles, 18–19 Styloglossus, 244–245 Stylohyoid muscles, 18, 158–159 Stylopharyngeus, 260–261 Subarachnoid space, 21 Subclavius, 83 Subcortical structures, 399–402 Subcostals, 100 Subglottal pressure, 113 Subglottic air pressure, phonation and, 181 pressure, 181 space, 181 Sublingual salivary glands, 230 Submandibular salivary glands, 230 Submucous fibrous layer, 239 Successional teeth, 234 Sulci, 378 Sulcus central, 393 lateral, 393 Summating potential (SP), 350 Superadded teeth, 234 Superficial defined, 7 anatomy, defined, 2 Superior auricular, ligaments, 318 cerebellar peduncles, 403 colliculus, 353 defined, 7 laryngeal nerve (SLN) external branch of, 138 internal branch of, 138 vagus nerve, 42 ligament, ossicular, 323 longitudinal muscle, 239–240 olivary complex (SOC), 352 semicircular canal, 331 temporal gyrus, 353 Supine, defined, 7 Supra, defined, 7 Suprahyoid, 155 muscles, 18, 19 Suprasegmental properties of speech, 189 Surface anatomy, defined, 2 Surfaces approximal, 235

buccal, 235 dental, 234–235 labial, 235 lingual, 234 occlusal, 234 Surfactant, 70 Sustained phonation, 188 Sutura dentata, 25 limbosa, 25 serrata, 25 Sutures, 24 intermaxillary, 198 Swallow reflex, protection during, 168 Swallowing central pattern generators, 288 deglutition and, 287–291 described, 287–288 mastication and, 287–291 pharyngeal absence of, 295 delayed, 295 pharyngeal stage, described, 297–302 Sympathetic nervous system, 21 Symphysis, 25 Synapses, 21 Synaptic transmission, 371, 372 Synarthrodial joints, 25 Synchondrosis, 25, 26 vertebrosternal ribs and, 58 Syndesmosis, 25 Synovial fluid, 25, 277 joints, 26, 277 membrane, 25 Syphilis, 363 Systematic anatomy, defined, 2

T TA (Terminologia Anatomica), 5 Taste buds, 308 sense of, 308 Tectorial membrane, 330, 347 Teeth articulation and, 275–276 deciduous, 232, 233 mixed dentition stage, 234 occlusion, 235–236 oral preparatory stage and, 289 475

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Teeth  (continued) permanent, 232, 234 successional, 234 superadded, 234 types of, 231–234 underbite, 236 Tegmental wall, middle ear, 326 Temporal bones, 207–208 facial nerve branch, 38 gyrus, superior, 353 lobes, 353, 396–398 parieto-occipital association area, 353 Temporalis, 247, 248 fossa, 247 Temporomandibular joint (TMJ), 16, 17, 195, 277 syndrome, 25 Tendons, 14 Tensor tympani, contraction acoustic reflex, 323 Tensor veli palatini, 264, 344 TEOAEs (Transient-evoked emissions), 359–360 Terminal respiratory bronchioles, 68 Termination, vocal folds, 188 Terminologia Anatomica (TA), 5 Terms, contrasting pairs of, 7 Tertiary bronchi, 68 Tesla, Nikola, 315 Thalamus, 399, 405–406 limbic system and, 408 Thoracic esophagus, 297 fixation, 66, 168 vertebrae, 53–54 views of, 54 Thorax accessory muscles of inspiration anterior, 80–83 posterior, 87–92 Throat, clearing/coughing, 168 Thrombocytes, 18 Thyroarytenoid muscle, 136, 153, 155, 173 superior view, 137 Thyroepiglottic ligament, 145 Thyrohyoid membrane, 142, 147 middle ligament, 147 muscle, 141, 161, 162 Thyroid cartilage, 133, 134, 141 gland, 141

Thyropharyngeal muscle, 258 Thyropharyngeus muscle, 258 Tidal expiration, 114 inspiration, 114 Tidal volume (TV), 114 Tinnitus, 364 Tissues chart of, 12 defined, 1 TLC (Total lung capacity), 119 TMJ (Temporomandibular joint), 16, 17, 195, 277 syndrome, 25 Tongue articulation and, 268 muscles and, 268–269 consonant production and, 269 muscles of, 239–245 extrinsic, 241–245 intrinsic muscles of, 239–241 oral preparatory stage and, 290 pharyngeal stage, 294 vowel production and, 269–270 Tonotopic, 353 organization, 350 Tonsillar branch, glossopharyngeal nerve, 40 Tonsillitis, 237 Tooth anatomy of, 230–231 bicuspids, 232 cuspids, 232 incisors, 232 molars, 232 Topographic anatomy, defined, 2 Total lung capacity (TLC), 119 Trachea, 66–68, 67 fracture of, 145 Tragus, 317 Transduction cochlea, 348–351 organ of Corti and, 329 Transformer action, 341 Transient-evoked emissions (TEOAEs), 359–360 Transverse abdominis, 96–97 facial muscles, 214–216 horizontal/axial/transaxial plane, 9 muscles, 212, 241 processes, 60 vertebra, 50 Transversus thoracis, 99, 100 476

Index

Trapezius, 91–92 Trapezoid body, 352 Traumatic ossicular chain discontinuity, 342 Treacher Collins, 196, 282 Triangular fossa, 316 Trigeminal nerve, 36–37 Trisomy 13, 196 Triticeal, 147 Trochlear nerve, 36 Tubercle, of rib, 58 Tunnel of Corti, 329 TV (Tidal volume), 114 Tympani, scala, 328, 329, 345 Tympanic branch, glossopharyngeal nerve, 40 membrane, 319–321 movement of, 341–344 perforated, 363 secondary, 324 sulcus, 319 Tympanogram, 358 Tympanometry, 358 Tympanosclerosis, 363

Velopharyngeal insufficiency, 282, 283 port, 279 Velum, 236 articulation and, 279–282 defined, 279 depressors, 254–255 elevators of, 253–254 muscles of, 252–255 pharyngeal stage, 294 resonance and, 279–282 Ventilation, 126 Ventral anterior (belly), 7 defined, 7 Ventricular folds, 138 superior view, 139 system, brain, 379–382 Venturi, Giovanni Battista, 180 Venturi tube effect, Bernoulli effect and, 180–181 Vermilion border, 267, 267 zones, 267 Vertebrae attachments between, 59 identification of, 50 Vertebral arteries, 412 column, 49 divisions of, 49, 51–56 foramen, 50 ribs, foramen, 58 Vertebrochondral ribs, 58 Vertebrosternal ribs, 58 Vertical muscle, 241 phase difference, 172 Vestibular branch, vestibulocochlear nerve, 38 folds, 138 system, 331–332 Vestibular system, 354 Vestibule, 327–328 Vestibuli, scala, 328, 329 Vestibulocochlear nerve, 38–39, 332–333, 349 Vestibulo-ocular reflex, 402 VFSS (Videofluoroscopic swallow study), 302–303 Vibration amplitude of, 179, 180 aperiodic, 185, 186 period of, 185

U Umbo, tympanic membrane and, 320 Unami, 308 Uncrossed fibers, 353 Underbite, 236 Unilateral innervation, 38 Unpaired cartilages, 141–146 Upper esophageal sphincter, 297 espiratory tract, 64, 65 Utricle branch inner ear, 332 vestibulocochlear nerve, 39 U-tube manometer, 121–122 Uvula, 236

V Vagus nerve, 40–42, 139 branches of, 138 Valleculae, 145, 238 Valsalva maneuver, 66 Vascularis, stria, 329 VC (Vital capacity), 119 Vegetative respiration, 108–109 speech breathing and, 110 477

Fundamentals of Anatomy and Physiology of Speech, Language, and Hearing

Vibration  (continued) regularity/periodicity of, 185–186 Vibratory cycle, for vocal folds, 174 motion, sound, 338 Videofluoroscopic swallow study (VFSS), 302–303 Videokymography, 185 Viral physiology, defined, 4 Visceral pleura, 70 pleural, 70 thorax, 64–72 respiratory passages, 64 Visual agnosia, 398 cortex associated, 398 primary, 398 Visuospatial processing, 385 Vital capacity (VC), 119 Vocal attack, 188 glottal, 188 ligament, 136 superior view, 137 nodules, 184 process, 140 register, 186–187 track cavities of, 226–227 described, 226 Vocal folds, 133 cavities of, 271 closure, 182–183, 184 incomplete, 184 epithelium, folds, 136 false, 138 gap, anterior/posterior, 182 healthy, 177 movement of, intensity changes and, 180 termination, 188 vibration, frequency and, 174 vibratory cycle for, 174 Vocalis muscle, 141 superior view, 137 Voice acoustic parameters of, 186 coordinate structures of, 169 fundamental frequency of, 174–179 parameters of, 174–182

elasticity, 174 inertia, 174 stiffness, 174 production, 172 Vomer, 203 von Békésy, Gorg, 315, 345 von Helmholtz, Hermann, 315 Vowels production of diphthongs, 273–274 source-filter theory of, 271–272 tongue and, 269 tongue positions during, 272 quadrilateral, 272–273

W Web spirometer, 123 “Wedge-and-groove” joint, 25 Wernicke, Carl, 386, 387 Wernicke aphasia, 387 area, 387, 396, 398 conduction aphasia and, 388 language skills and, 353 Whistle register, 188 White blood cells, 14, 18 fibrous connective tissue, 14 matter, 21, 23, 371, 372 Whole-nerve action potential, 350

X Xyphoid, 57

Y Yellow fibrous connective tissue, 14, 15

Z Zenker diverticulum, 301 Zone of language, 387 Zygomatic arch, 200 bones, 200 facial nerve branch, 38 major, 219–220 process, 197

478