Applied Muscle Action and Co-ordination 9781487583132

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Applied Muscle Action and Co-ordination

APPLIED MUSCLE ACT ION AND CO-ORD I NATION

Kathleen I. McMurrich Lecturer, Department of Anatomy University of Toronto

UNIVERSITY OF TORONTO PRESS

Copyright©, Canada, 1957, by University of Toronto Press Printed in Canada Reprinted in 2018 ISBN 978-1-4875-8185-5 (paper)

London: Oxford University Press

To the best and wisest of fathers James Playfair McMurrich

PREFACE THE OBJECT OF nns BOOK is to provide the basic knowledge of muscle action and co-ordination by which the student of Occupational Therapy can apply specific techniques to specific conditions of muscle insufficiency for the restoration of function. It is taken for granted that the use of this book has been preceded by the study of anatomy and physiology; therefore, anatomical data, such as the origins and insertions of the muscles, the course and distribution of the nerves of supply and the joints of the body, have been omitted as mere repetition of facts presented in authoritative textbooks of anatomy. Use of handicrafts and games for curative purposes must be based upon knowledge of the muscles involved in such activities. Suggestions are made for those which will involve certain muscles or muscle groups, but these suggestions by no means form a complete list. The ingenious therapist with a sound knowledge of muscle action can constantly make appropriate additions. For the student it is hoped that the accounts of the signs of nerve lesions and of the falsifications of movement which so often accompany these lesions will be useful. The book is the result of many years experience in teaching anatomy to students of Occupational and Physical Therapy. The difficulties of the subject-matter have been noted and the introductory chapter is an endeavour to clarify these problems for the beginner as well as to summerize existing knowledge of muscle action for the more advanced reader. I am deeply grateful to Dr. J. V. Basmajian, formerly of the University of Toronto, now Professor of Anatomy at Queen's University, Kingston, Ontario, and to Dr. A. T. Jousse, Director of Physical and Occupational Therapy at the University of Toronto, for the interest and encouragement they have given me in connection with this textbook. Miss Muriel Driver, of Warm Springs, Georgia, Miss Amy DesBrisay of Sunnybrook Veterans' Hospital, Toronto, and Miss Isabel Robinson of the Staff in Occupational Therapy, University of Toronto, have kindly given much assistance about craft work. I should like to express here my thanks to Miss Margaret Murphy for typing the manuscript, to Mrs. N. B. Allan and Mrs. Marian Dougan for the drawings made for illustration, and to the Workmen's Compensation Board of Ontario and Toronto General Hospital for the photographs. The courtesy shown me at all times by the University of Toronto Press has been most appreciated. K. I. McM.

CONTENTS Preface

vii

Introduction

3

PART I

MUSCLES OF THE UPPER EXTREMITY Muscles of the Pectoral Girdle

19

Muscles Moving the Shoulder Joint

26

Muscles of the Arm

34

Muscles of the Forearm

37

Muscles of the Hand

49

PARTII

MUSCLES OF THE LOWER EXTREMITY Muscles Moving the Hip Joint

59

Muscles of the Leg

70

PART III

MUSCLES OF THE TRUNK

Muscles of the Abdominal Wall

83

Muscles of the Back

85

Muscles of the Neck

87

Bibliography

91

PLATES facing page Ulnar nerve lesion

38

Median and ulnar nerve injury

38

Radial nerve injury showing typical position of wrist

38

Arm-raising exercise

39

Resistance exercise for Posterior Deltoid and Rhomboids

54

Exercise for Triceps and wrist extensors

55

Applied Muscle Action and

Co-ordination

INTRODUCTION THE ACTIONS of muscles have been noted for centuries by people studying the structure of the body. Until the fourteenth century, religious prohibitions prevented dissection of the human body. Aristotle ( 384322 B.C.) and Galen ( A.D. 129-199) stated frankly that their observations were made upon animals. The latter, a Greek physician and philosopher, gave us the first systematic account of muscles, so complete, indeed, that thirteen centuries elapsed before the appearance of any comparable work. It was Galen who noted that if a flexor muscle was cut, the limb remained extended. He also noticed that if a muscle was cut, the parts contracted away from the cut, that a nerve passed to each muscle, and that if such a nerve was cut, the muscle could no longer contract. He believed that psychic force entered the muscle through this nerve-we call it nerve impulse-and his term "innate contractility" was long in use. Until the middle of the sixteenth century, Galen's works were the final authority. True, Leonardo da Vinci ( 1492-1519) left notebooks in which he had made drawings and notes on dissections of the human body, but these were mislaid and scattered so that it was not until the close of the nineteenth century that his anatomical studies were available to the scientific world. They revealed that Leonardo's observations were far in advance of his time in accuracy and extent. Apart from other important data which he noted, Leonardo must be credited with establishing the general rule that when one muscle contracts there is relaxation of its antagonist. This is an interesting foreshadowing of the law of "reciprocal innervation" of antagonistic muscles worked out by Sherrington at the beginning of this century. Andreas Vesalius ( 1514-64) was the first anatomist to break away from the Galenic tradition in a published text. In his great and wonderfully illustrated work De Corpora Humani Fabrica, Vesalius turned attention to specifically human dissections and discussed muscles in groups according to their actions. Since Vesalius, innumerable writers have paved the way for our modern text-books on anatomy and kinesiology. It might be mentioned that Fallopius ( 1523-62) was the first to ascribe to the Interossei of the hand the actions of Hexion of the first phalanx and extension of the second and third phalanges. In 1749 there was published a text-book on anatomy which became so popular that it was translated into

4

APPLIED MUSCLE ACTION AND CO-ORDINATION

many languages. This was An Anatomical Exposition af the Structure of the Human Body by Jacques Benigne Winslow. Winslow, who was Danish, held the post of "Professor of Physick, Anatomy and Surgery" at the University of Paris. In his book, a large section describes the muscles and their actions in such a way that, after 200 years, it is still worthy of study. Until the discovery was made that muscles respond to stimulation by electric current, most of the information on muscle action could only be deduced from observations of the cadaver and the living body. When Duchenne of Boulogne ( 1805-75) walked the wards of the Paris hospitals during the Franco-Prussian war with his home-made faradic battery, he accumulated data on the actions of muscles that are still authoritative. He proved that no muscle acts alone; each is part of a functional complex. His book, Physiologie des mouvements, which can be found in most medical libraries and which has recently been translated into English (I), is an invaluable source of information for the student of kinesiology. One of the important works setting forth the functional viewpoint was the lecture delivered in 1904 to the Royal College of Physicians by Charles Edward Beevor. This lecture, which was one of a memorial series known as the Croonian Lectures, deals with the upper extremity of the body only. It was published in book form but is no longer obtainable1 ; nevertheless, if a copy is available in an accessible medical library, it will be found to provide a searching study of the parts played by individual muscles in the movements of the upper limb. Succeeding generations of anatomists, physiologists and neurologists have studied the muscles of the body and the problems of contraction and relaxation. Tests by sundry methods have been made but the last word has not been said. The complexity of the mechanics of movement is so great that research has yet to solve the problem fully. Too much stress has been laid, perhaps, on the actions of individual muscles. It is essential that these be understood, but in the simplest movement more than one muscle is almost invariably involved, each playing its specific part in the performance of the desired movement. Text-books of anatomy describe the actions of each muscle, give a general account of "how muscles act," and outline the intricate pathways of nervous control. Clinical observations have shown the effect that paralysis of certain muscles can have on the performance of certain movements. The variety of movements of the body is infinite, and the lTh.is has just been edited and reprinted by Macmillan & Co. Ltd. for the guarantors of "Brain."

INTRODUCTION

5

study of how these movements are brought about has endless fascination. The actions of muscles may be studied in several ways: 1. In the anatomical laboratory on a cadaver. The student in demonstration classes should take careful note of the features of each muscle studied under the following headings: (a) The situation of the muscle in the body. ( b) The exact attachments of the muscle to bone or other structures and the form of each attachment, whether fibrous, by tendon, or by aponeurosis. ( c) The relationship of the muscle to a joint or joints. Does it pass over more than one joint? Does it pass over the joint anteriorly or posteriorly or at one side? Is the direction straight or oblique? ( d) The size of the muscle and its architecture. Do the fibres run straight from one attachment to the other or are they attached diagonally into the tendon? Do all the fibres run in the same direction? Is one part of the muscle larger or thicker than another? ( e) The relationship of the muscle to other muscles. Is it deep to other muscles or does it lie superficial to them? (f) The nerve supply. From which nerve does the muscle derive branches of supply? Do these branches enter the muscle from below or above or from the side? Where does the nerve enter the muscle, in its upper part or its lower part? ( g) The relationship of the larger blood vessels to the muscle. In this way, the student can provide himself with a mental picture of the muscles of the different regions of the body as a guide to the location of these muscles on the living subject. Further, certain muscles are so deeply placed that they are difficult or impossible to identify on the living subject; observation of their position and direction of pull on the cadaver provides information on their action. Gluteus Minimus is too deep to be felt, but it passes over the side of the hip joint and therefore it is assumed that it raises the lower limb to the side (abduction) . The mental picture thus formed can be tested by making drawings from memory of the region studied and practice in this is urged upon every student. 2. By observation and palpation on the living body. By this method we can see and feel the various muscles when they are acting. Some muscles can be felt in their entirety, swelling and hardening as they contract, and some are best identified at their tendons: for example the tendons crossing the back of the wrist. Other muscles may only be demonstrated by the resulting movement, deduced from observations

6

APPLIED MUSCLE ACTION AND CO-ORDINATION

in the anatomy class. Muscle identification on the living body requires practice-a great deal of practice-on yourself or on a partner. If a pathological condition exists, the inability to perform certain movements, or the unbalanced performance of a movement, indicates the muscular involvement. Accuracy in detecting this involvement of a few or many muscles in pathological conditions is of vital importance, as a clue to rehabilitation. The study of muscle action in the living should be intensive and should be preceded by anatomical knowledge. 3. By electrical stimulation. Muscular contraction can be induced by the application of electric current. Galvanic current stimulates the intrinsic contractility of the muscle fibres, independent of nerve supply. Faradic current affects the motor nerve and therefore elicits no response if the nerve is damaged. Faradic muscle-testing is commonly used to detect nerve degeneration in peripheral nerve lesions and also to determine regeneration following surgical repair, although voluntary contraction is usually detectable before there is response to faradic stimulation. A newer form of measurement of muscle power is chronaxie, using galvanic current but measured in time, the time required to produce contraction. These methods of eliciting muscular contraction, however, do not give accurate information on the action of many deep-seated muscles unless the superficial muscles are definitely paralysed. Moreover, the stimulus may spread to several muscles and thus blur the response of one definite muscle. 4. By clinical observation. Muscles are only too often either weakened or paralysed by disease or injury. The absence of contraction in a muscle may prove its function by allowing other muscles involved in a shared movement to overplay their part. Imbalance in the power of the muscles moving a joint can cause deformity. This occurs most markedly in the foot. Facts learned earlier in the anatomical laboratory and in study on the living body are proved-or perhaps disproved-in close observation of clinical cases. 5. Electromyography. This is a recent method of studying and proving the degree of contraction of a given muscle in the performance of a given movement in the living body. The "action potentials" of a muscle are picked up by an electrode and recorded with amplification in the same way as an electro-cardiogram is recorded. Structure of Voluntary Muscle

The essential peculiarity of muscle tissue is its ability to contract and relax. The fleshy belly of a muscle is the part that has this characteristic. In order that a contraction may bring about movement, a muscle must be attached to the bony skeleton and pass over at least

INTRODUCTION

7

one joint. The attachments of a muscle are known as ongm and insertion. The attachment nearer the mid-line of the body, to the usually fixed point, is called the origin; the attachment further from the midline, to the usually moving part, is called the insertion. Between these two attachments lies the contractile belly of the muscle.

FIGURE

1

The belly of a muscle is composed of thousands of cells, threadlike, cylindrical or prismatic in shape, each fibre covered by a delicate elastic membrane called the sarcolemma which is considered part of the fibre. These cells, or fibres, are subject to great variation in diameter and length but are always larger than other cells of the body. The number of fibres in the various muscles may be anything from a few hundred to several thousand. Under the microscope, a muscle fibre shows a transversely striped appearance and many nuclei, normally at the periphery, hence it is described as a multi-nuclear cell. Two types of voluntary muscle fibres are described, red and pale, intermingled; some muscles are composed predominantly of red fibres ( such as Soleus), while other muscles are predominantly white-fibred ( Gastrocnemius) .2 Muscles that have a majorty of red fibres contract slowly but endure longer; muscles that are mainly composed of pale fibres can contract quickly but soon tire. A muscle, as a whole, is enclosed in a sheath of connective tissue. From this covering, strands penetrate the muscle substance separating groups of muscle fibres into bundles ( fasciculi). As these bundles 2Recent research by E . M. Walls would seem to reject this statement for human anatomy ( !27).

I

APPLIED MUSCLE ACTION AND CO-ORDINATION

subdivide into smaller bundles, the connective tissue partitions become thinner until they eventually form a delicate network separating individual muscle fibres. The connective tissue element of a muscle supports the muscle fibres and retains the innumerable blood capillaries and is continuous with the attachments of the muscle. These attachments take various forms : tendons, aponeuroses, raphae or fleshy. Tendons are cord- or bandlike lengths of white fibrous tissue, of varying lengths, such as the tendons of insertion of the muscles of the forearm. If the tendon is Battened and broad like a membrane, it is called an aponeurosis: for example, the aponeurosis of the External Oblique muscle of the abdominal wall. A few muscles begin in a fibrous band called a raphe: for example, the origin of the Buccinator muscle in the face. Some muscles arise from a considerable area and leave no appreciable mark on the bone, showing that the connective tissue that invests bundles of muscle fibres has blended with the periosteum of the bone. Brachialis is an example of this type of attachment which is known as a fleshy attachment. Tendons attaching to bone have been found to penetrate into the bone substance so that in the process of growth they have become incorporated with the bone. The site of the attachment of a tendon may be indicated by a protuberance such as the radial tuberosity, where force is concentrated upon a small area. Certain muscles are attached to structures other than bone: to cartilage, as in the larynx; to fascia, like Platysma, to the tendons of other muscles, like the Lumbricales. Since muscles, like engines, work and move, they are provided with devices to help them avoid "wear and tear." In a region where pressure is great, or considerable friction would result from tendon rubbing against bone, protection is provided by bursae-small sacs containing a minimal amount of synovial fluid. Bursae are found between tendon and bone ( between the tendon of Biceps and the radial tuberosity) or between tendon and ligament (between the tendon of Psoas and the capsule of the hip joint). Occasionally, as in the latter example, a bursa may open into the joint cavity. Bursae are also present between the skin and bony projections, such as the prepatellar bursa between the skin and the patella at the knee. Another protection against friction, which also increases the efficiency of the muscle, is provided by sesamoid bones. These are small, round bones imbedded in tendons ( sesame = seed). Sesamoid bones are found regularly at the metatarso-phalangeal joint of the great toe, at the metacarpo-phalangeal joint of the thumb, and at the knee joint-the patella being actually a sesamoid bone though dignified with a title of its own. Occasionally they develop in other tendons. They lie

INTRODUCTION

9

against the proximal bone of the joint, never opposite the joint proper, and, by holding the tendon away from close contact with the joint, they increase the mechanical advantage of the muscle. Where tendons are long, they must be retained in position and this is done by bands of dense connective tissue, thickenings of the deep, investing fascia of the limb, known as retinacula. To prevent the long tendons of the forearm or leg muscles from standing out like bowstrings when the wrist or ankle is flexed or extended, retinacula are present immediately above the joints, the tendons lying each in its own slot within the retaining band. On the flexor surface of the toes and fingers individual retinacula are found. These fibrous sheaths are attached to the borders of the phalanges, passing over the tendons of the long digital Bexors. Where tendons are thus held in a bony hollow, a lubricating device is provided by the elongated bursae, called synovial sheaths. These are double-layered tubes containing synovial fluid which assures smooth gliding of the tendons in their confined position. Since movement stimulates the excretion of synovia, over-exertion of a specific muscle provided with a synovial sheath can cause a condition known as teno-synovitis-inflammation of a tendon or sheath. Typists and musicians not uncommonly develop this painful condition. Every voluntary muscle must be connected with the central nervous system in order to receive the impulse to contract or to relax. Centres in the brain initiate and control this impulse to the muscles required for the desired movement. These impulses travel down the spinal cord to the specific level and are there transmitted to the cells of the anterior grey column and from thence, through peripheral nerves, to the required muscles. A nerve enters a muscle at a point where it will be least disturbed by the contraction of the muscle; this is called the "motor point," imp~rtant for electrical stimulation. Within the muscle the nerve branches out until each muscle fibre receives at least one efferent nerve filament, sometimes more. Each efferent filament ends within the sarcolemma of the muscle fibre in a "motor end-plate" where minute amounts of acetylcholine are discharged by the filament. Afferent (sensory) fibres accompany the efferent fibres into a muscle but are less numerous. Some end in small bundles of thin muscle fibres known as "neuro-muscular spindles" and convey to the central nervous system information on the state of tension within the muscle. Other afferent nerve fibres end at the junction of the muscle belly with its tendon in "neuro-tendinous spindles." Fibres from the autonomic nervous system also enter a muscle to innervate the walls of the blood vessels within that muscle.

10

APPLIED MUSCLE ACTION AND CO-ORDINATION

When Sherrington proved reciprocal innervation, at the beginning of this century, he verified the observations of Leonardo da Vinci that, when a muscle contracts, its antagonist relaxes. Recent physiological experiments have shown that it is the afferent nerve endings within the muscle which induce this reciprocity in the performance of any given movement. Any voluntary movement is, in fact, made in response to some impulse carried by afferent nerve fibres which may have either an excitatory or inhibitory effect upon the cells of the anterior grey column of the spinal cord. The mechanism of this has not yet been clearly demonstrated. These afferent nerve endings are responsible for the reflex contraction which maintains posture and position, known as "muscle tone." The maintenance of tone requires very little oxygen, since only a few muscle fibres are contracting and those in relaysasynchronously. It has been generally accepted that anti-gravity muscles exhibit the most "tone"; certainly it is recognized that the muscles of the back of the neck cannot be completely relaxed ( 15). The existence of muscle tone is, at present, the subject of much debate, as the action potentials in electromyography tests are absent in a "resting muscle." When a muscle is so stretched that it is in danger of being overstretched, it contracts protectively: this is known as the "stretch reflex." Muscles with the best tone exhibit the stretch reflex most definitely. When a very heavy weight is carried in the hand, keeping the elbow joint extended, the elbow flexors contract and soon become fatigued. Obviously this reflex must arise from the afferent nerve endings within the muscle. In certain pathological conditions, the stretch reflex may become markedly increased, but it is a property of normal muscles, particularly of those concerned with the maintenance of the upright position in man. The neurone is the structural and functional unit of the nervous system. The countless number of neurones of the nervous system are linked together in contiguity but not continuity. The terminal arborizations of the axon ( efferent process) of a neurone are in contact but not continuous with the arborizations of the dendrites ( afferent processes) of other neurones. These points of contact are known as synapses. The complexity of the inter-relations between neurones is a subject for the neurologist and physiologist. It has been stated ( 14) that one cell of the anterior grey column of the spinal cord may receive impulses from a thousand other cells. The spinal cord is so dependent on the higher levels of the nervous system that, when these directing influences are suddenly cut off, the cord is thrown "out of gear" and some time must elapse before it regains its primitive powers of

INTRODUCTION

11

independent activity. A cell of the anterior grey column ( or the motor cell of a cranial nerve), its efferent fibres, and its related group of muscle fibres constitute the physiological "motor unit." Each efferent fibre of a unit supplies several muscle fibres, ranging from 5-150, depending upon the number of fibres constituting the muscle; in the anti-gravity muscles of the limbs, the motor unit may be 150 muscle fibres; small muscles used in precision movements may have many small units. The strength of a muscle contraction is dependent upon the number of motor units stimulated to contract; when all the motor units of a given muscle are excited, the muscle is then in maximal contraction. If the continuity of a motor neurone is interrupted, the muscle fibres which it supplies are paralysed. If the nerve itself is injured, the whole muscle becomes flaccid, eventually degenerating until only connective tissue remains. If the cell body in or near the spinal cord is destroyed, there can be no regeneration, but if only the peripheral nerve is interrupted, and surgical repair is made promptly, regeneration will take place. Muscles are richly supplied with blood. The larger arteries send branches into the muscle which divide and subdivide until they finally break up into capillaries. The smallest arterial branches anastomose freely within the muscle. Veins accompany all but the smaller arteries, and muscular activity promotes the flow of blood through these veins, the contraction of the muscles forcing out the blood. Muscles ( particularly of the extremities) are the main sources of the body's heat as well as being the "engines of the body." Best and Taylor declare that "the efficiency of the muscular machine is comparable to that of the best type of gas engine," the principal fuel for this "machine" being carbohydrate. Exercise increases the supply of blood to muscles, up to five or six times the supply of resting muscles, if the exercise is strenuous. When exercise is carried beyond the capacity of the circulatory arrangements, fatigue results. Forms of Muscle

Muscles vary greatly in size and form. The muscles of the middle ear are minute, while the large muscle of the buttock, Gluteus Maximus, is a coarsely built muscle of surprising size. Some muscles are thin and flat, some are thick and round; some are wider than they are long, while some are longer than they are wide. There are muscles that have more than one attachment at the proximal end but only one point of attachment at the distal end, for example, Biceps Brachii. Or a muscle may spread out at its insertion to attach to several bones, for example, Tibialis Posterior. The muscles of the vertebral column have

J2

APPLIED MUSCLE ACTION AND CO.ORDINATION

FIGURE

2

FIGURE

3

FIGURE

4

a continuous series of attachments along the length of the column. Functionally, the difference in muscles may be summed up as follows: (a) If the fibres of a muscle run parallel to the long axis of the muscle, they are long but relatively few, able to lift a light weight through considerable distance. Parallel-fibred muscles are built for speed rather than for power. Included in this classification are muscles with a flattened appearance, sometimes long and straplike, such as Sartorius (Figure 2), sometimes rectangular, such as Pronator Quadratus ( Figure 3), or triangular, such as Adductor Pollicis ( Figure 4). ( b) If the fibres of a muscle run obliquely to the long axis of the muscle, they are shorter and more numerous, able to lift a heavy weight through a short distance. Obliquely fibred muscles are built

INTRODUCTION

13

FIGURE 6. First Dorsal lnterosseus: bi-pennate.

FIGURE 5. Extensor Digitorum Longus: unipennate.

FIGURE 7. Deltoid-acromial fibres: multipennate.

for power. They are called pennate muscles because of their resemblance to a feather (pinna= feather), the tendon being the quill and the muscle fibres the barbs. If the tendon is at one side with the fibres converging to it from a narrow area the muscle is classified as unipennate, for example, Extensor Digitorum Longus (Figure 5). If the fibres converge from both sides from a broad area to a central tendon, the muscle is classified as bi-pennate, for example, First Dorsal Interosseus ( Figure 6). If septa extend into the muscle, providing several bi-pennate arrangements in one muscle, the muscle is classified as multi-pennate, for example, the middle part of Deltoid (Figure 7). A few voluntary muscles surrounding orifices of the body, known as sphincter muscles, take a circular course in a greater or lesser degree. An example of this type is Orbicularis Oculi ( Figure 8).

14

APPLIED MUSCLE ACTION AND CO-ORDINATION

F1cuRE 8. Orbicularis Oculi: sphincter.

Names of Muscles

Many students approach the study of anatomy or kinesiology with the feeling that they are about to study another language. The majority of terms used to describe parts of the body have derived from Latin, a few from Greek, and some are named for the man who first described them. Muscles were apparently named from particular features, such as their shape, position, function, or general or specific appearance. If the student has been fortunate enough to have learned Latin at school, the names of most of the muscles will be self-explanatory. Muscles Named by Shape Trapezius. The two muscles together form a trapezoid, a geometrical figure where no two sides are parallel. Deltoid. Shaped like the Greek letter t::.. (Delta). Quadratus Femoris, Pronator Quadratus. Rectangular, four-sided muscles ( Figure 3) . Rhomboids. Another geometrical figure, a rectangle on a slant. Piriformis. Pear-shaped. round like a Teres Ma;or and Minor; Pronator Teres. Teres cylinder or tube. Therefore, Teres Major is the larger round muscle; Teres Minor, the smaller round muscle. Pronator Teres is the round muscle that pronates the forearm in contrast to Pronator Quadratus, the square muscle that pronates.

=

Muscles Named by Position Supraspinatus. Above the spine ( of the scapula). Infraspinatus. Below the spine. Subscapularis. Under the scapula.

INTRODUCTION

=

15

Peroneus Longus, Peroneus Brevis. Peroneus fibula: therefore, these are the long and short fibular muscles. Interossei. "Between bones": these are small muscles lying between the metacarpal or metatarsal bones. Flexor Digitorium Profundus. The deep (profound) muscle that :flexes the fingers (digits) in contrast to Flexor Digitorum Sublimis, the superficial ( sublime, above) muscle that :flexes the fingers. Muscles Named by Action Flexor Carpi Ulnaris. The muscle that :flexes the carpus to the ulnar side. Adductor Pollicis. The muscle that adducts the thumb (pollux). Sartorius. Sartor tailor: traditionally, a tailor sat cross-legged at his work, the position to which this muscle brings the hip and knee.

=

Muscles Named by Appearance belly; nemius twin : the muscle has Gastrocnemius. Gastric two heads of origin. Semitendinosus. The muscle is tendinous in its lower half ( semi half). Semimembranosus, on the contrary, is membranous in its upper half. Rectus Femoris. The straight ( direct) muscle of the femur. The muscles mentioned are examples of self-explanatory nomenclature; the names of all muscles have meaning and are clues to the necessary knowledge.

=

=

=

Muscle Work

Each muscle of the body has its specific action or actions, but only in extremely rare instances does one muscle act alone. Other muscles co-operate, control, prevent auxiliary actions, or steady the fixed point or the body itself. Any one muscle can play a different role in diflerent movements of the body or part of the body, depending on the position of the body or the movement desired. These roles have been classified under the following headings. ( 1) A muscle can act as a prime mover when its specific action brings about the desired movement: for example, Flexor Carpi Ulnaris :flexes the wrist. ( 2) A muscle can act as the antagonist to the action of the prime mover, preventing that action or controlling it by gradual relaxation : Flexor Carpi Ulnaris is antagonistic to the extensor action of Extensor Carpi Ulnaris. ( 3) A muscle can act as a synergist to the action of a prime mover

16

APPLIED MUSCLE ACTION AND CO-ORDINATION

by steadying the proximal joint over which the prime mover could effect movement, thus concentrating the power of the muscular contraction upon the desired movement. Extensor Digitorum extends the fingers, passing also over the wrist joint; in quick, strong extension of the fingers, Flexor Carpi Ulnaris contracts synergically to steady the wrist joint and prevent weakening of the extension of the fingers. ( 4) A muscle can act as a fixator to steady the proximal part (origin) of a prime mover: Flexor Carpi Ulnaris contracts strongly to steady the pisiform bone in abduction of the fifth finger by Abductor Digiti Minimi. The co-operation of muscles in the movements at the joints of the body will be described throughout this text. In considering muscle action, the effect of gravity must be remembered. If gravity will bring about the desired movement, the muscles usually required need not contract unless force is necessary, or resistance is met. The :Oexors of the wrist need not contract if the hand is held palm down as in waving your hand, but if you slap the table hard, or press hard against the resisting surface, they can be felt to contract. The position of the body, or part of the body, can bring about an apparent contradiction in the stated facts of muscle action. On certain unusual occasions, the so-called insertion may become the fixed point and the origin the moving part. Biceps Brachii usually flexes the elbow but, if you perform the gymnastic exercise of "chinning yourself' on the bar, the hand and forearm are the fixed point and the arm is approximated to the forearm, instead of the forearm to the arm. In both movements, the movement at the joint is the same: :Oexion. In walking, first one foot and then the other become the fixed points and the muscles of the lower extremities act from below upward to bring the body into alignment with the fixed point of the foot.

MUSCLES OF THE PECTORAL GIRDLE is the focal point for all movements of the pectoral girdle: that is, the clavicle and scapula. The scapula is suspended from the lateral end of the clavicle by the coraco-clavicular ligaments and attached to the clavicle by the capsule of the acromioclavicular joint. Therefore, all movements of the scapula, caused by contraction of the various muscles attached to it, must be referred to the clavicle and thence to the sterno-clavicular joint. THE STERNO-CLAVICULAR JOINT

MOVEMENTS OF

Scapular Movements

Clavicular Movements ( medial end)

Elevation

THE

PECTORAL GIRDLE

Muscles

Movement Restricted By

Downward

Upper Trapezius Levator Anguli Scapulae Rhomboids

Costo-clavicular ligament Coraco-clavicular ligaments

Depression

Upward

Relaxation of elevating muscles

plus rotation down of glenoid

plus rotation on long axis

Lower Trapezius Rhomboids Levator

Contact of clavicle with first rib

Retraction

Forward

Middle Trapezius Rhomboids

Inter-clavicular ligament

Protraction

Backward

Serratus ( upper digitations)

Downward

Serratus

plus rotation on long axis

Trapezius

Backward plus rotation on long axis

Pectoralis Minor

plus rotation upwards of glenoid or plus forward movement of superior border

Conoid ligament

Trapezius

The Trapezius muscles are the most superficial muscles of the back of the neck and upper part of the back. The muscle is sometimes described as consisting of four parts: ( 1) the fibres from the occipital bone to the clavicle; ( 2) the fibres from the ligamentum nuchae to the acromion and spine of the scapula; ( 3 ) the horizontal fibres to the

20

APPLIED MUSCLE ACTION AND CO-ORDINATION

tubercle of the spine of the scapula; and ( 4) the fibres from the lower thoracic vertebrae to the "concentration area" at the tubercle of the scapular spine. The second part is the strongest and thickest; the fourth is markedly the thinnest and weakest. It should be noted that the triangular apex of the spine of the scapula receives no muscle attachment but, rather, is worn smooth by the passage of the middle part of the muscle which is here aponeurotic as it crosses the small area of bone to the tubercle. Trapezius is an important fixator muscle of the scapula and acts in all arm-raising movements to steady the origin of the muscles of the arm. The upper fibres elevate the point of the shoulder as in shrugging. When the arm is elevated above 90°, the tip of the shoulder is raised accordingly, by the upper part of Trapezius. If a heavy weight, such as a suitcase, is carried in the hand at the end of the down-stretched arm, this part of Trapezius contracts to counteract the downward drag. The middle fibres of the muscle are directed horizontally and so act most efficiently in retraction ( bringing the scapula back toward the vertebral