Clinical anatomy by regions 9th ed r snell (lippincott, 2012) 1

Basic Anatomy 7Fasciae The fasciae of the body can be divided into two types— superficial and deep—and lie between the skin and the underlying muscles and bones.. Internal Structure of

CLINICAL ANATOMY

BY REGIONS

N I N T H E D I T I O N

C L I N I C A L A N A T O M Y

B Y R E G I O N S

Richard ร Snell, M.R.C.S., L.R.C.P., M.B., B.S., M.D., Ph.D

Emeritus Professor of Anatomy

(formerly Chairman of the Department of Anatomy)

George Washington University

School of Medicine and Health Sciences

Washington, District of Columbia

Previously

Associate Professor of Anatomy and Medicine, Yale University Medical School

Lecturer in Anatomy, King's College, University of London

Visiting Professor of Anatomy, Harvard Medical School

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1 Human anatomy I Title

[DNLM: 1 Anatomy, Regional 2 Body Regions—anatomy & histology QS 4]

QM23.2.S55 2012

612—dc23

2011020326 DISCLAIMER

Care has been taken to confirm the accuracy of the information present and to describe generally accepted practices 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 con- tents of the publication Application of this information in a particular situation remains the profes- sional responsibility of the practitioner; the clinical treatments described and recommended may not

be considered absolute and universal recommendations.

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9 8 7 6 5 4 3 2 1

P R E F A C E

This book provides medical students, dental students, allied

health students, and nursing students with a basic

knowl-edge of anatomy that is clinically relevant

In this new edition, further efforts have been made to

weed out unnecessary material and reduce the size of the

text The following changes have been introduced

1 The text and tables have been reviewed and trimmed

where necessary

2 All the illustrations have been reviewed and some

have been discarded where duplication occurs

3 The anatomy of common medical procedures has

been carefully reviewed Sections on the

complica-tions caused by the ignorance of normal anatomy

have been retained

4 The Clinical Problems and Review Questions are

available online at www.thePoint.lww.com/Snell9e

Each chapter of Clinical Anatomy is constructed in a

similar manner This gives students ready access to

mate-rial and facilitates moving from one part of the book to

another Each chapter is divided into the following

catego-ries:

1 Clinical Example: A short case report that dramatizes

the relevance of anatomy in medicine introduces each

chapter

2 Chapter Objectives: This section focuses the student on

the material that is most important to learn and

under-stand in each chapter It emphasizes the basic structures

in the area being studied so that, once mastered, the

stu-dent is easily able to build up his or her knowledge base

This section also points out structures on which

exam-iners have repeatedly asked questions

3 Basic Clinical Anatomy: This section provides basic

information on gross anatomic structures that are of clinical importance Numerous examples of normal radiographs, CT scans, MRI studies, and sonograms are also provided Labeled photographs of cross-sectional anatomy of the head, neck, and trunk are included to stimulate students to think in terms of three-dimen-sional anatomy, which is so important in the interpreta-tion of imaging studies

4 Surface Anatomy: This section provides surface

land-marks of important anatomic structures, many of which are located some distance beneath the skin This section

is important because most practicing medical personnel seldom explore tissues to any depth beneath the skin

5 Clinical Problem Solving and Review Questions:

Available online at www.thePoint.lww.com, the purpose of these questions is threefold: to focus atten-tion on areas of importance, to enable students to assess their areas of weakness, and to provide a form of self- evaluation for questions asked under examination con-ditions Many of the questions are centered around a clinical problem that requires an anatomic answer

To assist in the quick understanding of anatomic facts, the book is heavily illustrated Most figures have been kept simple, and color has been used extensively Illustrations summarizing the nerve and blood supply of regions have been retained, as have overviews of the distribution of cra-nial nerves

R.S.S

Finally, I wish to express my deep gratitude to the staff of Lippincott Williams & Wilkins for their great help and support

in the preparation of this new edition

A C K N O W L E D G M E N T S

C O N T E N T S

Preface vAcknowledgments vii

CHAPTER 3 The Thorax: Part II—The Thoracic Cavity 58

CHAPTER 4 The Abdomen: Part I—The Abdominal Wall 113

CHAPTER 5 The Abdomen: Part II—The Abdominal Cavity 156

CHAPTER 7 The Pelvis: Part II—The Pelvic Cavity 262

Appendix 720Index 723

A

C H A P T E R 1

INTRODUCTION

65-year-old man was admitted to the emergency department complaining of the sudden

onset of a severe crushing pain over the front of the chest spreading down the left arm

and up into the neck and jaw On questioning, he said that he had had several attacks of

pain before and that they had always occurred when he was climbing stairs or digging in the

gar-den Previously, he found that the discomfort disappeared with rest after about 5 minutes On this

occasion, the pain was more severe and had occurred spontaneously while he was sitting in a

chair; the pain had not disappeared

The initial episodes of pain were angina, a form of cardiac pain that occurs on exertion and

disap-pears on rest; it is caused by narrowing of the coronary arteries so that the cardiac muscle has

insuf-ficient blood The patient has now experienced myocardial infarction, in which the coronary blood flow

is suddenly reduced or stopped and the cardiac muscle degenerates or dies Myocardial infarction is

the major cause of death in industrialized nations Clearly, knowledge of the blood supply to the heart

and the arrangement of the coronary arteries is of paramount importance in making the diagnosis and

treating this patient

C H A P T E R O U T L I N E

Basic Anatomy 2

Descriptive Anatomic Terms 2

Terms Related to Position 2

Terms Related to Movement 3

Basic Structures 3

Skin 3

Fasciae 7

Muscle 7 Joints 11 Ligaments 15 Bursae 15 Synovial Sheath 15 Blood Vessels 16 Lymphatic System 18

Nervous System 20 Mucous Membranes 27 Serous Membranes 27 Bone 28

Cartilage 32 Effects of Sex, Race, and Age on Structure 32

C H A P T E R O B J E C T I V E S

■

■ It is essential that students understand the terms used for

describing the structure and function of different regions of

gross anatomy Without these terms, it is impossible to describe

in a meaningful way the composition of the body Moreover, the

physician needs these terms so that anatomic abnormalities

found on clinical examination of a patient can be accurately recorded.

■

■ This chapter also introduces some of the basic structures that compose the body, such as skin, fascia, muscles, bones, and blood vessels.

2 ChAPTer 1 Introduction

cannot accurately discuss or record the abnormal functions

of joints, the actions of muscles, the alteration of position of organs, or the exact location of swellings or tumors

Terms Related to PositionAll descriptions of the human body are based on the assumption that the person is standing erect, with the upper limbs by the sides and the face and palms of the hands

directed forward (Fig 1.1) This is the so-called anatomic position The various parts of the body are then described

in relation to certain imaginary planes

Median Sagittal Plane

This is a vertical plane passing through the center of the body, dividing it into equal right and left halves (see Fig 1.1) Planes situated to one or the other side of

the median plane and parallel to it are termed paramedian

A structure situated nearer to the median plane of the body

than another is said to be medial to the other Similarly, a

structure that lies farther away from the median plane than

another is said to be lateral to the other.

Basic anatomy

Anatomy is the science of the structure and function of the

body

Clinical anatomy is the study of the macroscopic

struc-ture and function of the body as it relates to the practice of

medicine and other health sciences

Basic anatomy is the study of the minimal amount of

anatomy consistent with the understanding of the overall

structure and function of the body

Descriptive Anatomic Terms

It is important for medical personnel to have a sound

knowledge and understanding of the basic anatomic terms

With the aid of a medical dictionary, you will find that

understanding anatomic terminology greatly assists you in

the learning process

The accurate use of anatomic terms by medical

person-nel enables them to communicate with their colleagues both

nationally and internationally Without anatomic terms, one

superior

paramedian plane

median sagittal plane

proximal end of upper limb

lateral border

distal end of upper limb medial border

dorsal surface

of foot plantar surface

of foot inferior

palmar surface

of hand

dorsal surface

of hand posterior anterior

horizontal or

transverse

plane

coronal plane median sagittal plane

FIGURE 1.1 Anatomic terms used in relation to position Note that the subjects are standing in the anatomic position.

Basic Anatomy 3

Rotation is the term applied to the movement of a part of the body around its long axis Medial rotation is

the movement that results in the anterior surface of the

part facing medially Lateral rotation is the movement

that results in the anterior surface of the part facing laterally

Pronation of the forearm is a medial rotation of the

forearm in such a manner that the palm of the hand faces

posteriorly (see Fig 1.3) Supination of the forearm is a

lateral rotation of the forearm from the pronated tion so that the palm of the hand comes to face anteriorly (see Fig 1.3)

posi-Circumduction is the combination in sequence of the

movements of flexion, extension, abduction, and tion (see Fig 1.2)

adduc-Protraction is to move forward; retraction is to move

backward (used to describe the forward and backward movement of the jaw at the temporomandibular joints)

Inversion is the movement of the foot so that the sole faces in a medial direction (see Fig 1.3) Eversion is the

opposite movement of the foot so that the sole faces in a lateral direction (see Fig 1.3)

Basic Structures

SkinThe skin is divided into two parts: the superficial part, the

epidermis; and the deep part, the dermis (Fig 1.4) The

epidermis is a stratified epithelium whose cells become tened as they mature and rise to the surface On the palms of the hands and the soles of the feet, the epidermis is extremely thick, to withstand the wear and tear that occurs in these regions In other areas of the body, for example, on the ante-rior surface of the arm and forearm, it is thin The dermis is composed of dense connective tissue containing many blood vessels, lymphatic vessels, and nerves It shows considerable variation in thickness in different parts of the body, tending

flat-to be thinner on the anterior than on the posterior surface

It is thinner in women than in men The dermis of the skin

is connected to the underlying deep fascia or bones by the

superficial fascia, otherwise known as subcutaneous tissue.

The skin over joints always folds in the same place, the

SKIN CREASES (Fig 1.5) At these sites, the skin is thinner

than elsewhere and is firmly tethered to underlying tures by strong bands of fibrous tissue

struc-The appendages of the skin are the nails, hair follicles,

sebaceous glands, and sweat glands.

The nails are keratinized plates on the dorsal surfaces of

the tips of the fingers and toes The proximal edge of the

plate is the root of the nail (see Fig 1.5) With the exception

of the distal edge of the plate, the nail is surrounded and

overlapped by folds of skin known as nail folds The face of skin covered by the nail is the nail bed (see Fig 1.5) Hairs grow out of follicles, which are invaginations

sur-of the epidermis into the dermis (see Fig 1.4) The cles lie obliquely to the skin surface, and their expanded

folli-extremities, called hair bulbs, penetrate to the deeper part

of the dermis Each hair bulb is concave at its end, and the

Coronal Planes

These planes are imaginary vertical planes at right angles to

the median plane (see Fig 1.1)

Horizontal, or Transverse, Planes

These planes are at right angles to both the median and the

coronal planes (see Fig 1.1)

The terms anterior and posterior are used to indicate

the front and back of the body, respectively (see Fig 1.1)

To describe the relationship of two structures, one is said to

be anterior or posterior to the other insofar as it is closer to

the anterior or posterior body surface

In describing the hand, the terms palmar and dorsal

surfaces are used in place of anterior and posterior, and in

describing the foot, the terms plantar and dorsal surfaces

are used instead of lower and upper surfaces (see Fig 1.1)

The terms proximal and distal describe the relative distances

from the roots of the limbs; for example, the arm is proximal

to the forearm and the hand is distal to the forearm

The terms superficial and deep denote the relative

distances of structures from the surface of the body, and

the terms superior and inferior denote levels relatively

high or low with reference to the upper and lower ends

of the body

The terms internal and external are used to describe the

relative distance of a structure from the center of an organ

or cavity; for example, the internal carotid artery is found

inside the cranial cavity and the external carotid artery is

found outside the cranial cavity

The term ipsilateral refers to the same side of the body;

for example, the left hand and the left foot are ipsilateral

Contralateral refers to opposite sides of the body; for

example, the left biceps brachii muscle and the right rectus

femoris muscle are contralateral

The supine position of the body is lying on the back

The prone position is lying face downward.

Terms Related to Movement

A site where two or more bones come together is known

as a joint Some joints have no movement (sutures of the

skull), some have only slight movement (superior

tibiofib-ular joint), and some are freely movable (shoulder joint)

Flexion is a movement that takes place in a sagittal

plane For example, flexion of the elbow joint

approxi-mates the anterior surface of the forearm to the anterior

surface of the arm It is usually an anterior movement, but

it is occasionally posterior, as in the case of the knee joint

(see Fig 1.2) Extension means straightening the joint and

usually takes place in a posterior direction (see Fig 1.2)

Lateral flexion is a movement of the trunk in the coronal

plane (Fig 1.3)

Abduction is a movement of a limb away from the

mid-line of the body in the coronal plane (see Fig 1.2)

Adduction is a movement of a limb toward the body in the

coronal plane (see Fig 1.2) In the fingers and toes, abduction

is applied to the spreading of these structures and adduction

is applied to the drawing together of these structures (see

Fig 1.3) The movements of the thumb (see Fig 1.3), which

are a little more complicated, are described on page 413

concavity is occupied by vascular connective tissue called

hair papilla A band of smooth muscle, the arrector pili,

connects the undersurface of the follicle to the superficial

part of the dermis (see Fig 1.4) The muscle is innervated

by sympathetic nerve fibers, and its contraction causes the

hair to move into a more vertical position; it also presses the sebaceous gland and causes it to extrude some

com-of its secretion The pull com-of the muscle also causes dimpling

of the skin surface, so-called gooseflesh Hairs are

dis-tributed in various numbers over the whole surface of the

Basic Anatomy 5

body, except on the lips, the palms of the hands, the sides

of the fingers, the glans penis and clitoris, the labia minora

and the internal surface of the labia majora, and the soles

and sides of the feet and the sides of the toes

Sebaceous glands pour their secretion, the sebum, onto

the shafts of the hairs as they pass up through the necks

of the follicles They are situated on the sloping

undersur-face of the follicles and lie within the dermis (see Fig 1.4)

Sebum is an oily material that helps preserve the flexibility

of the emerging hair It also oils the surface epidermis around the mouth of the follicle

Sweat glands are long, spiral, tubular glands distributed

over the surface of the body, except on the red margins of the lips, the nail beds, and the glans penis and clitoris (see Fig 1.4) These glands extend through the full thickness of the dermis, and their extremities may lie in the superficial fascia The sweat glands are therefore the most deeply pen-etrating structures of all the epidermal appendages

supination of forearm pronation of forearm

FIGURE 1.3 Additional anatomic terms used in relation to movement.

FIGURE 1.4 General structure of the skin and its relationship

to the superficial fascia Note that hair follicles extend down

into the deeper part of the dermis or even into the

super-ficial fascia, whereas sweat glands extend deeply into the

superficial fascia.

nail root nail

nail bed

terminal phalanx nail folds

FIGURE 1.5 The various skin creases on the palmar surface

of the hand and the anterior surface of the wrist joint The relationship of the nail to other structures of the finger is also shown.

Skin Infections

The nail folds, hair follicles, and sebaceous glands are

com-mon sites for entrance into the underlying tissues of pathogenic

organisms such as Staphylococcus aureus Infection occurring

between the nail and the nail fold is called a paronychia Infection

of the hair follicle and sebaceous gland is responsible for the

com-mon boil A carbuncle is a staphylococcal infection of the

superfi-cial fascia It frequently occurs in the nape of the neck and usually

starts as an infection of a hair follicle or a group of hair follicles.

Sebaceous Cyst

A sebaceous cyst is caused by obstruction of the mouth of a

sebaceous duct and may be caused by damage from a comb or

by infection It occurs most frequently on the scalp.

Shock

A patient who is in a state of shock is pale and exhibits

goose-flesh as a result of overactivity of the sympathetic system, which

causes vasoconstriction of the dermal arterioles and contraction

of the arrector pili muscles.

Skin Burns

The depth of a burn determines the method and rate of healing

A partial-skin-thickness burn heals from the cells of the hair

follicles, sebaceous glands, and sweat glands as well as from the cells at the edge of the burn A burn that extends deeper than the sweat glands heals slowly and from the edges only, and con- siderable contracture will be caused by fibrous tissue To speed

up healing and reduce the incidence of contracture, a deep burn should be grafted.

Skin Grafting Skin grafting is of two main types: split-thickness grafting and

full-thickness grafting In a split-thickness graft, the greater part of the epidermis, including the tips of the dermal papillae,

is removed from the donor site and placed on the recipient site This leaves at the donor site for repair purposes the epidermal cells on the sides of the dermal papillae and the cells of the hair follicles and sweat glands.

A full-thickness skin graft includes both the epidermis and the dermis and, to survive, requires rapid establishment of a new cir- culation within it at the recipient site The donor site is usually covered with a split-thickness graft In certain circumstances, the full-thickness graft is made in the form of a pedicle graft, in which

a flap of full-thickness skin is turned and stitched in position at the recipient site, leaving the base of the flap with its blood supply intact at the donor site Later, when the new blood supply to the graft has been established, the base of the graft is cut across.

C L I N I C A L N O T E S

Basic Anatomy 7

Fasciae

The fasciae of the body can be divided into two types—

superficial and deep—and lie between the skin and the

underlying muscles and bones

The superficial fascia, or subcutaneous tissue, is a

mix-ture of loose areolar and adipose tissue that unites the

dermis of the skin to the underlying deep fascia (Fig 1.6)

In the scalp, the back of the neck, the palms of the hands,

and the soles of the feet, it contains numerous bundles of

collagen fibers that hold the skin firmly to the deeper

struc-tures In the eyelids, auricle of the ear, penis and scrotum,

and clitoris, it is devoid of adipose tissue

The deep fascia is a membranous layer of connective

tis-sue that invests the muscles and other deep structures (see Fig

1.6) In the neck, it forms well-defined layers that may play an

important role in determining the path taken by pathogenic

organisms during the spread of infection In the thorax and

abdomen, it is merely a thin film of areolar tissue covering

the muscles and aponeuroses In the limbs, it forms a

defi-nite sheath around the muscles and other structures, holding

them in place Fibrous septa extend from the deep surface of

the membrane, between the groups of muscles, and in many

places divide the interior of the limbs into compartments (see

Fig 1.6) In the region of joints, the deep fascia may be

consid-erably thickened to form restraining bands called retinacula

(Fig 1.7) Their function is to hold underlying tendons in

posi-tion or to serve as pulleys around which the tendons may move

Fasciae and Infection

A knowledge of the arrangement of the deep fasciae often

helps explain the path taken by an infection when it spreads

from its primary site In the neck, for example, the various

fascial planes explain how infection can extend from the

region of the floor of the mouth to the larynx.

C L I N I C A L N O T E S

MuscleThe three types of muscle are skeletal, smooth, and cardiac

Skeletal Muscle

Skeletal muscles produce the movements of the skeleton;

they are sometimes called voluntary muscles and are made

up of striped muscle fibers A skeletal muscle has two or more attachments The attachment that moves the least is

referred to as the origin, and the one that moves the most, the insertion (Fig 1.8) Under varying circumstances, the

lateral intermuscular septum

brachialis humerus cephalic vein musculocutaneous nerve biceps

FIGURE 1.6 Section through the middle of the right arm

showing the arrangement of the superficial and deep fascia

Note how the fibrous septa extend between groups of

muscles, dividing the arm into fascial compartments.

extensor tendons and their synovial

sheaths

extensor retinaculum

FIGURE 1.7 Extensor retinaculum on the posterior surface

of the wrist holding the underlying tendons of the extensor muscles in position.

8 ChAPTer 1 Introduction

common tendon for the insertion

of the gastrocnemius and

soleus muscles

external oblique aponeurosis

raphe of mylohyoid muscles

A B

C

FIGURE 1.9 Examples of (A) a tendon, (B) an aponeurosis,

and (C) a raphe.

degree of mobility of the attachments may be reversed;

therefore, the terms origin and insertion are interchangeable

The fleshy part of the muscle is referred to as its belly

(see Fig 1.8) The ends of a muscle are attached to bones,

cartilage, or ligaments by cords of fibrous tissue called

tendons (Fig 1.9) Occasionally, flattened muscles are

attached by a thin but strong sheet of fibrous tissue called

an aponeurosis (see Fig 1.9) A raphe is an

interdigita-tion of the tendinous ends of fibers of flat muscles (see

Fig 1.9)

Internal Structure of Skeletal Muscle

The muscle fibers are bound together with delicate areolar

tissue, which is condensed on the surface to form a fibrous

envelope, the epimysium The individual fibers of a muscle

are arranged either parallel or oblique to the long axis of the

muscle (Fig 1.10) Because a muscle shortens by one third

to one half its resting length when it contracts, it follows

that muscles whose fibers run parallel to the line of pull will bring about a greater degree of movement compared with those whose fibers run obliquely Examples of muscles with parallel fiber arrangements (see Fig 1.10) are the ster-nocleidomastoid, the rectus abdominis, and the sartorius.Muscles whose fibers run obliquely to the line of pull are

referred to as pennate muscles (they resemble a feather) (see Fig 1.10) A unipennate muscle is one in which the

tendon lies along one side of the muscle and the muscle fibers pass obliquely to it (e.g., extensor digitorum lon-

gus) A bipennate muscle is one in which the tendon lies

in the center of the muscle and the muscle fibers pass to it

from two sides (e.g., rectus femoris) A multipennate cle may be arranged as a series of bipennate muscles lying

mus-alongside one another (e.g., acromial fibers of the deltoid)

or may have the tendon lying within its center and the cle fibers passing to it from all sides, converging as they go (e.g., tibialis anterior)

For a given volume of muscle substance, pennate cles have many more fibers compared to muscles with par-allel fiber arrangements and are therefore more powerful;

mus-in other words, range of movement has been sacrificed for strength

Skeletal Muscle ActionAll movements are the result of the coordinated action of many muscles However, to understand a muscle’s action, it

is necessary to study it individually

A muscle may work in the following four ways:

Prime mover: A muscle is a prime mover when it is the

chief muscle or member of a chief group of muscles responsible for a particular movement For example, the quadriceps femoris is a prime mover in the movement

of extending the knee joint (Fig 1.11)

Antagonist: Any muscle that opposes the action of the

prime mover is an antagonist For example, the biceps femoris opposes the action of the quadriceps femoris when the knee joint is extended (see Fig 1.11) Before a prime mover can contract, the antagonist muscle must

be equally relaxed; this is brought about by nervous reflex inhibition

Fixator: A fixator contracts isometrically (i.e., contraction

increases the tone but does not in itself produce ment) to stabilize the origin of the prime mover so that it can act efficiently For example, the muscles attaching the shoulder girdle to the trunk contract as fixators to allow the deltoid to act on the shoulder joint (see Fig 1.11)

move-Synergist: In many locations in the body, the prime mover

muscle crosses several joints before it reaches the joint at which its main action takes place To prevent unwanted movements in an intermediate joint, groups of muscles

called synergists contract and stabilize the intermediate

joints For example, the flexor and extensor muscles of the carpus contract to fix the wrist joint, and this allows the long flexor and the extensor muscles of the fingers to work efficiently (see Fig 1.11)

These terms are applied to the action of a particular cle during a particular movement; many muscles can act

mus-as a prime mover, an antagonist, a fixator, or a synergist, depending on the movement to be accomplished

Basic Anatomy 9

rhomboid

quadrilateral strap strap with

tendinous intersections

fusiform two bellies two headed triangular

FIGURE 1.10 Different forms of the internal structure of skeletal muscle A relaxed and a contracted muscle are also shown; note how the muscle fibers, on contraction, shorten by one third to one half of their resting length Note also how the mus- cle swells.

Muscles can even contract paradoxically, for example,

when the biceps brachii, a flexor of the elbow joint,

con-tracts and controls the rate of extension of the elbow when

the triceps brachii contracts

Nerve Supply of Skeletal Muscle

The nerve trunk to a muscle is a mixed nerve, about

60% is motor and 40% is sensory, and it also contains

some sympathetic autonomic fibers The nerve enters

the muscle at about the midpoint on its deep surface,

often near the margin; the place of entrance is known

as the motor point This arrangement allows the

mus-cle to move with minimum interference with the nerve trunk

Naming of Skeletal MusclesIndividual muscles are named according to their shape, size, number of heads or bellies, position, depth, attach-ments, or actions Some examples of muscle names are shown in Table 1.1

Muscle Tone

Determination of the tone of a muscle is an important clinical

examination If a muscle is flaccid, then either the afferent, the

efferent, or both neurons involved in the reflex arc necessary for

the production of muscle tone have been interrupted For example,

if the nerve trunk to a muscle is severed, both neurons will have

been interrupted If poliomyelitis has involved the motor anterior

horn cells at a level in the spinal cord that innervates the muscle,

the efferent motor neurons will not function If, conversely, the

muscle is found to be hypertonic, the possibility exists of a lesion

involving higher motor neurons in the spinal cord or brain.

Muscle Attachments

The importance of knowing the main attachments of all the major

muscles of the body need not be emphasized Only with such

knowledge is it possible to understand the normal and abnormal actions of individual muscles or muscle groups how can one even attempt to analyze, for example, the abnormal gait of a patient without this information?

Muscle Shape and Form

The general shape and form of muscles should also be noted, since a paralyzed muscle or one that is not used (such as occurs when a limb is immobilized in a cast) quickly atrophies and changes shape In the case of the limbs, it is always worth remembering that a muscle on the opposite side of the body can

be used for comparison.

C L I N I C A L N O T E S

extensor digitorum extensor carpi

radialis

flexor digitorum profundus flexor carpiradialis

femo-C Muscles around shoulder girdle fixing the scapula so that movement of abduction can take place at the shoulder joint

D Flexor and extensor muscles of the carpus acting as synergists and stabilizing the carpus so that long flexor and extensor

tendons can flex and extend the fingers.

Smooth Muscle

Smooth muscle consists of long, spindle-shaped cells closely

arranged in bundles or sheets In the tubes of the body, it

provides the motive power for propelling the contents

through the lumen In the digestive system, it also causes

the ingested food to be thoroughly mixed with the digestive

juices A wave of contraction of the circularly arranged

fib-ers passes along the tube, milking the contents onward By

their contraction, the longitudinal fibers pull the wall of the

tube proximally over the contents This method of

propul-sion is referred to as peristalsis.

In storage organs such as the urinary bladder and the

uterus, the fibers are irregularly arranged and interlaced

with one another Their contraction is slow and sustained and brings about expulsion of the contents of the organs

In the walls of the blood vessels, the smooth muscle fibers are arranged circularly and serve to modify the caliber of the lumen

Depending on the organ, smooth muscle fibers may

be made to contract by local stretching of the fibers, by nerve impulses from autonomic nerves, or by hormonal stimulation

Cardiac Muscle

Cardiac muscle consists of striated muscle fibers that branch and unite with each other It forms the myocardium

Basic Anatomy 11

Joints

A site where two or more bones come together, whether

or not movement occurs between them, is called a joint

Joints are classified according to the tissues that lie between the bones: fibrous joints, cartilaginous joints, and synovial joints

Fibrous Joints

The articulating surfaces of the bones are joined by fibrous tissue (Fig 1.12), and thus very little movement is possible The sutures of the vault of the skull and the inferior tibi-ofibular joints are examples of fibrous joints

Cartilaginous Joints

Cartilaginous joints can be divided into two types: primary

and secondary A primary cartilaginous joint is one in

which the bones are united by a plate or a bar of hyaline

cartilage Thus, the union between the epiphysis and the

of the heart Its fibers tend to be arranged in whorls and

spirals, and they have the property of spontaneous and

rhythmic contraction Specialized cardiac muscle fibers

form the conducting system of the heart.

Cardiac muscle is supplied by autonomic nerve fibers

that terminate in the nodes of the conducting system and

in the myocardium

Necrosis of Cardiac Muscle

The cardiac muscle receives its blood supply from the

coro-nary arteries A sudden block of one of the large branches of a

coronary artery will inevitably lead to necrosis of the cardiac

muscle and often to the death of the patient.

12 ChAPTer 1 Introduction

skull

skull bone periosteum suture

fibrous joint

skull bone periosteum

posterior longitudinal ligament ligamentum flavum

cartilaginous joint

supraspinous ligament

interspinous ligament

anterior longitudinal ligament

fibrocartilaginous intervertebral disc

fatty pad

synovial joint

diaphysis of a growing bone and that between the 1st rib

and the manubrium sterni are examples of such a joint No

movement is possible

A secondary cartilaginous joint is one in which the

bones are united by a plate of fibrocartilage and the

articu-lar surfaces of the bones are covered by a thin layer of

hya-line cartilage Examples are the joints between the vertebral

bodies (see Fig 1.12) and the symphysis pubis A small

amount of movement is possible

Synovial Joints

The articular surfaces of the bones are covered by a thin layer

of hyaline cartilage separated by a joint cavity (see Fig 1.12) This arrangement permits a great degree of freedom of

movement The cavity of the joint is lined by synovial membrane, which extends from the margins of one articu-

lar surface to those of the other The synovial membrane

is protected on the outside by a tough fibrous membrane

Basic Anatomy 13

referred to as the capsule of the joint The articular surfaces

are lubricated by a viscous fluid called synovial fluid, which

is produced by the synovial membrane In certain synovial

joints, for example, in the knee joint, discs or wedges of

fibrocartilage are interposed between the articular surfaces

of the bones These are referred to as articular discs.

Fatty pads are found in some synovial joints lying

between the synovial membrane and the fibrous capsule

or bone Examples are found in the hip (see Fig 1.12) and

knee joints

The degree of movement in a synovial joint is limited

by the shape of the bones participating in the joint, the

coming together of adjacent anatomic structures (e.g., the

thigh against the anterior abdominal wall on flexing the

hip joint), and the presence of fibrous ligaments uniting

the bones Most ligaments lie outside the joint capsule, but

in the knee some important ligaments, the cruciate

liga-ments, lie within the capsule (Fig 1.13).

Synovial joints can be classified according to the

arrange-ment of the articular surfaces and the types of movearrange-ment

that are possible

■

■ Plane joints: In plane joints, the apposed articular

sur-faces are flat or almost flat, and this permits the bones

to slide on one another Examples of these joints are the

sternoclavicular and acromioclavicular joints (Fig 1.14)

■

■ Hinge joints: Hinge joints resemble the hinge on a door,

so that flexion and extension movements are possible

Examples of these joints are the elbow, knee, and ankle

joints (see Fig 1.14)

■

■ Pivot joints: In pivot joints, a central bony pivot is

sur-rounded by a bony–ligamentous ring (see Fig 1.14), and

rotation is the only movement possible The atlantoaxial

and superior radioulnar joints are good examples

■

■ Condyloid joints: Condyloid joints have two distinct

convex surfaces that articulate with two concave

sur-faces The movements of flexion, extension,

abduc-tion, and adduction are possible together with a small

amount of rotation The metacarpophalangeal joints or

knuckle joints are good examples (see Fig 1.14)

■

■ Ellipsoid joints: In ellipsoid joints, an elliptical convex

articular surface fits into an elliptical concave articular surface The movements of flexion, extension, abduction, and adduction can take place, but rotation is impossible The wrist joint is a good example (see Fig 1.14)

■

■ Saddle joints: In saddle joints, the articular surfaces are

reciprocally concavoconvex and resemble a saddle on

a horse’s back These joints permit flexion, extension, abduction, adduction, and rotation The best example

of this type of joint is the carpometacarpal joint of the thumb (see Fig 1.14)

■

■ Ball-and-socket joints: In and-socket joints, a

ball-shaped head of one bone fits into a socketlike concavity

of another This arrangement permits free movements, including flexion, extension, abduction, adduction, medial rotation, lateral rotation, and circumduction The shoulder and hip joints are good examples of this type of joint (see Fig 1.14)

Stability of Joints

The stability of a joint depends on three main factors: the shape, size, and arrangement of the articular surfaces; the ligaments; and the tone of the muscles around the joint.Articular Surfaces

The ball-and-socket arrangement of the hip joint (see Fig 1.13) and the mortise arrangement of the ankle joint are good examples of how bone shape plays an important role in joint stability Other examples of joints, however,

in which the shape of the bones contributes little or ing to the stability include the acromioclavicular joint, the calcaneocuboid joint, and the knee joint

noth-Ligaments

Fibrous ligaments prevent excessive movement in a joint

(see Fig 1.13), but if the stress is continued for an excessively long period, then fibrous ligaments stretch For example, the ligaments of the joints between the bones forming the arches

of the feet will not by themselves support the weight of the body Should the tone of the muscles that normally support

hemispherical

head of femur

cup-shaped acetabulum

knee joint hip joint

peroneus longus muscle holding

up lateral longitudinal arch

of right foot

cruciate ligaments

medial collateral ligament

peroneus ligament

arch of foot

FIGURE 1.13 The three main factors responsible for stabilizing a joint A Shape of articular surfaces B Ligaments C Muscle tone.