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Chapter 1 Introduction A 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 garden. 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 disappears on rest; it is caused by narrowing of the coronary arteries so that the cardiac muscle has insufficient 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. Chapter Objectives

  • 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.

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Basic Anatomy Anatomy is the science of the structure and function of the body. Clinical anatomy is the study of the macroscopic structure 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 personnel enables them to communicate with their colleagues both nationally and internationally. Without anatomic terms, one 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 Position All 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 (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. Coronal Planes These planes are imaginary vertical planes at right angles to the median plane (Fig. 1-1). Horizontal, or Transverse, Planes These planes are at right angles to both the median and the coronal planes (Fig. 1-1). The terms anterior and posterior are used to indicate the front and back of the body, respectively (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 (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.

Figure 1-1 Anatomic terms used in relation to position. Note that the subjects are standing in the anatomic position.

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. P.3
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 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 tibiofibular 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 approximates 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 (Fig. 1-2). Extension means straightening the joint and usually takes place in a posterior direction (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 midline of the body in the coronal plane (Fig. 1-2). Adduction is a movement of a limb toward the body in the coronal plane (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 (Fig. 1-3). The movements of the thumb (Fig. 1-3), which are a little more complicated, are described on page 517. 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 (Fig. 1-3). Supination of the forearm is a lateral P.4
rotation of the forearm from the pronated position so that the palm of the hand comes to face anteriorly (Fig. 1-3).

Figure 1-2 Some anatomic terms used in relation to movement. Note the difference between flexion of the elbow and that of the knee.

Circumduction is the combination in sequence of the movements of flexion, extension, abduction, and adduction (Fig. 1-2). 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 (Fig. 1-3). Eversion is the opposite movement of the foot so that the sole faces in a lateral direction (Fig. 1-3). Basic Structures Skin The 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 flattened as P.5
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 anterior 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 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.

Figure 1-3 Additional anatomic terms used in relation to movement.

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 structures by strong bands of fibrous tissue. 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 (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 surface of skin covered by the nail is the nail bed (Fig. 1-5). Hairs grow out of follicles, which are invaginations of the epidermis into the dermis (Fig. 1-4). The follicles lie obliquely to the skin surface, and their expanded extremities, called hair bulbs, penetrate to the deeper part of the P.6
dermis. Each hair bulb is concave at its end, and the 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 (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 compresses the sebaceous gland and causes it to extrude some of its secretion. The pull of the muscle also causes dimpling of the skin surface, so-called gooseflesh. Hairs are distributed in various numbers over the whole surface of the 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.

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 superficial fascia, whereas sweat glands extend deeply into the superficial fascia.

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 undersurface of the follicles and lie within the dermis (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 (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 penetrating structures of all the epidermal appendages. P.7

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.

Clinical Notes Skin Infections The nail folds, hair follicles, and sebaceous glands are common 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 common boil. A carbuncle is a staphylococcal infection of the superficial 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 gooseflesh 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 considerable 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 dermis and, to survive, requires rapid establishment of a new circulation 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. P.8

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.

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 mixture 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 structures. In the eyelids, auricle of the ear, penis and scrotum, and clitoris, it is devoid of adipose tissue.

Figure 1-7 Extensor retinaculum on the posterior surface of the wrist holding the underlying tendons of the extensor muscles in position.

The deep fascia is a membranous layer of connective tissue that invests the muscles and other deep structures (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 definite 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 (Fig. 1-6). In the region of joints, the deep fascia may be considerably thickened to form restraining bands called retinacula (Fig. 1-7). Their function is to hold underlying tendons in position or to serve as pulleys around which the tendons may move. Clinical Notes 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. Muscle The 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 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 (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 (Fig. 1-9). A raphe is an interdigitation of the tendinous ends of fibers of flat muscles (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 P.9
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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 (Fig. 1-10) are the sternocleidomastoid, the rectus abdominis, and the sartorius.

Figure 1-8 Origin, insertion, and belly of the gastrocnemius muscle.
Figure 1-9 Examples of (A) a tendon, (B) an aponeurosis, and (C) a raphe.

Muscles whose fibers run obliquely to the line of pull are referred to as pennate muscles (they resemble a feather) (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 longus). 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 muscle may be arranged as a series of bipennate muscles lying alongside one another (e.g., acromial fibers of the deltoid) or may have the tendon lying within its center and the muscle fibers passing to it from all sides, converging as they go (e.g., tibialis anterior). For a given volume of muscle substance, pennate muscles have many more fibers compared to muscles with parallel fiber arrangements and are therefore more powerful; in other words, range of movement has been sacrificed for strength.

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 muscle swells.

Skeletal Muscle Action All 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 (Fig. 1-11). Before a prime mover can contract, the antagonist muscle must be equally relaxed; this is brought about by nervous reflex inhibition. P.11
    Figure 1-11 Different types of muscle action. A. Quadriceps femoris extending the knee as a prime mover, and biceps femoris acting as an antagonist. B. Biceps femoris flexing the knee as a prime mover, and quadriceps acting as an antagonist. 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.
  • Fixator: A fixator contracts isometrically (i.e., contraction increases the tone but does not in itself produce movement) 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 (Fig. 1-11).
  • 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 P.12
    muscles of the carpus contract to fix the wrist joint, and this allows the long flexor and extensor muscles of the fingers to work efficiently (Fig. 1-11).

These terms are applied to the action of a particular muscle during a particular movement; many muscles can act as a prime mover, an antagonist, a fixator, or a synergist, depending on the movement to be accomplished. Muscles can even contract paradoxically, for example, when the biceps brachii, a flexor of the elbow joint, contracts 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 muscle to move with minimum interference with the nerve trunk. Naming of Skeletal Muscles Individual muscles are named according to their shape, size, number of heads or bellies, position, depth, attachments, or actions. Some examples of muscle names are shown in Table 1-1. Clinical Notes 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. 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 fibers 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 propulsion 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 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. Clinical Notes Necrosis of Cardiac Muscle The cardiac muscle receives its blood supply from the coronary 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. 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 tibiofibular joints are examples of fibrous joints. P.13

Table 1-1 Naming of Skeletal Musclesa
Name Shape Size Number of Heads or Bellies Position Depth Attachments Actions
Deltoid Triangular
Teres Round
Rectus Straight
Major   Large
Latissimus   Broadest
Longissimus   Longest
Biceps     Two heads
Quadriceps     Four heads
Digastric     Two bellies
Pectoralis       Of the chest
Supraspinatus       Above spine of scapula
Brachii       Of the arm
Profundus         Deep
Superficialis         Superficial
Externus         External
Sternocleidomastoid           From sternum and clavicle to mastoid process
Coracobrachialis           From coracoid process to arm
Extensor             Extend
Flexor             Flex
Constrictor             Constrict
aThese names are commonly used in combination, for example, flexor pollicis longus (long flexor of the thumb).

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 bar of hyaline cartilage. Thus, the union between the epiphysis and the diaphysis of a growing bone and that between the first 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 articular surfaces of the bones are covered by a thin layer of hyaline cartilage. Examples are the joints between the vertebral bodies (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 (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 articular surface to those of the other. The synovial membrane is protected on the outside by a tough fibrous membrane 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 (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 ligaments, lie within the capsule (Fig. 1-13). Synovial joints can be classified according to the arrangement of the articular surfaces and the types of movement that are possible.

  • Plane joints: In plane joints, the apposed articular surfaces 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 (Fig. 1-14). P.14
    Figure 1-12 Examples of three types of joints. A. Fibrous joint (coronal suture of skull).B. Cartilaginous joint (joint between two lumbar vertebral bodies). C. Synovial joint (hip joint).
  • Pivot joints: In pivot joints, a central bony pivot is surrounded by a bony–ligamentous ring (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 surfaces. The movements of flexion, extension, abduction, and adduction are possible together with a small amount of rotation. The metacarpophalangeal joints or knuckle joints are good examples (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 (Fig. 1-14). P.15
    Figure 1-13 The three main factors responsible for stabilizing a joint. A. Shape of articular surfaces. B. Ligaments. C. Muscle tone.
  • 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 (Fig. 1-14).
  • Ball-and-socket joints: In ball-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 (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 (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 nothing to the stability include the acromioclavicular joint, the calcaneocuboid joint, and the knee joint. Ligaments Fibrous ligaments prevent excessive movement in a joint (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 the arches become impaired by fatigue, then the ligaments will stretch and the arches will collapse, producing flat feet. Elastic ligaments, conversely, return to their original length after stretching. The elastic ligaments of the auditory ossicles play an active part in supporting the joints and assisting in the return of the bones to their original position after movement. Muscle Tone In most joints, muscle tone is the major factor controlling stability. For example, the muscle tone of the short muscles around the shoulder joint keeps the hemispherical head of the humerus in the shallow glenoid cavity of the scapula. Without the action of these muscles, very little force would P.16
be required to dislocate this joint. The knee joint is very unstable without the tonic activity of the quadriceps femoris muscle. The joints between the small bones forming the arches of the feet are largely supported by the tone of the muscles of the leg, whose tendons are inserted into the bones of the feet (Fig. 1-13).

Figure 1-14 Examples of different types of synovial joints. A. Plane joints (sternoclavicular and acromioclavicular joints). B. Hinge joint (elbow joint). C. Pivot joint (atlantoaxial joint). D. Condyloid joint (metacarpophalangeal joint). E. Ellipsoid joint (wrist joint). F. Saddle joint (carpometacarpal joint of the thumb). G. Ball-and-socket joint (hip joint).

Nerve Supply of Joints The capsule and ligaments receive an abundant sensory nerve supply. A sensory nerve supplying a joint also supplies the muscles moving the joint and the skin overlying the insertions of these muscles, a fact that has been codified as Hilton’s law. Clinical Notes Examination of Joints When examining a patient, the clinician should assess the normal range of movement of all joints. When the bones of a joint are no longer in their normal anatomic relationship with one another, then the joint is said to be dislocated. Some joints are particularly susceptible to dislocation because of lack of support by ligaments, the poor shape of the articular surfaces, or the absence of adequate muscular support. The shoulder joint, temporomandibular joint, and acromioclavicular joints are good examples. Dislocation of the hip is usually congenital, being caused by inadequate development of the socket that normally holds the head of the femur firmly in position. The presence of cartilaginous discs within joints, especially weightbearing joints, as in the case of the knee, makes them particularly susceptible to injury in sports. During a rapid movement the disc loses its normal relationship to the bones and becomes crushed between the weightbearing surfaces. In certain diseases of the nervous system (e.g., syringomyelia), the sensation of pain in a joint is lost. This means that the warning sensations of pain felt when a joint moves beyond the normal range of movement are not experienced. This phenomenon results in the destruction of the joint. Knowledge of the classification of joints is of great value because, for example, certain diseases affect only certain types of joints. Gonococcal arthritis affects large synovial joints such as the ankle, elbow, or wrist, whereas tuberculous arthritis also affects synovial joints and may start in the synovial membrane or in the bone. Remember that more than one joint may receive the same nerve supply. For example, the hip and knee joints are both supplied by the obturator nerve. Thus, a patient with disease limited to one of these joints may experience pain in both. P.17
Ligaments A ligament is a cord or band of connective tissue uniting two structures. Commonly found in association with joints, ligaments are of two types. Most are composed of dense bundles of collagen fibers and are unstretchable under normal conditions (e.g., the iliofemoral ligament of the hip joint and the collateral ligaments of the elbow joint). The second type is composed largely of elastic tissue and can therefore regain its original length after stretching (e.g., the ligamentum flavum of the vertebral column and the calcaneonavicular ligament of the foot). Clinical Notes Damage to Ligaments Joint ligaments are very prone to excessive stretching and even tearing and rupture. If possible, the apposing damaged surfaces of the ligament are brought together by positioning and immobilizing the joint. In severe injuries, surgical approximation of the cut ends may be required. The blood clot at the damaged site is invaded by blood vessels and fibroblasts. The fibroblasts lay down new collagen and elastic fibers, which become oriented along the lines of mechanical stress. Bursae A bursa is a lubricating device consisting of a closed fibrous sac lined with a delicate smooth membrane. Its walls are separated by a film of viscous fluid. Bursae are found wherever tendons rub against bones, ligaments, or other tendons. They are commonly found close to joints where the skin rubs against underlying bony structures, for example, the prepatellar bursa (Fig. 1-15). Occasionally, the cavity of a bursa communicates with the cavity of a synovial joint. For example, the suprapatellar bursa communicates with the knee joint (Fig. 1-15) and the subscapularis bursa communicates with the shoulder joint. Synovial Sheath A synovial sheath is a tubular bursa that surrounds a tendon. The tendon invaginates the bursa from one side so that the tendon becomes suspended within the bursa by a mesotendon (Fig. 1-15). The mesotendon enables blood vessels to enter the tendon along its course. In certain situations, when the range of movement is extensive, the mesotendon disappears or remains in the form of narrow threads, the vincula (e.g., the long flexor tendons of the fingers and toes). Synovial sheaths occur where tendons pass under ligaments and retinacula and through osseofibrous tunnels. Their function is to reduce friction between the tendon and its surrounding structures. Clinical Notes Trauma and Infection of Bursae and Synovial Sheaths Bursae and synovial sheaths are commonly the site of traumatic or infectious disease. For example, the extensor tendon sheaths of the hand may become inflamed after excessive or unaccustomed use; an inflammation of the prepatellar bursa may occur as the result of trauma from repeated kneeling on a hard surface. P.18

Figure 1-15 A. Four bursae related to the front of the knee joint. Note that the suprapatellar bursa communicates with the cavity of the joint. B. Synovial sheaths around the long tendons of the fingers. C. How tendon indents synovial sheath during development, and how blood vessels reach the tendon through the mesotendon.

Blood Vessels Blood vessels are of three types: arteries, veins, and capillaries (Fig. 1-16). Arteries transport blood from the heart and distribute it to the various tissues of the body by means of their branches (Figs. 1-16 and 1-17). The smallest arteries, <0.1 mm in diameter, are referred to as arterioles. The joining of branches of arteries is called an anastomosis. Arteries do not have valves. Anatomic end arteries (Fig. 1-17) are vessels whose terminal branches do not anastomose with branches of arteries supplying adjacent areas. Functional end arteries are vessels whose terminal branches do anastomose with those of adjacent arteries, but the caliber of the anastomosis is insufficient to keep the tissue alive should one of the arteries become blocked. Veins are vessels that transport blood back to the heart; many of them possess valves. The smallest veins are called venules (Fig. 1-17). The smaller veins, or tributaries, unite to form larger veins, which commonly join with one another to form venous plexuses. Medium-size deep arteries are often accompanied by two veins, one on each side, called venae comitantes. Veins leaving the gastrointestinal tract do not go directly to the heart but converge on the portal vein; this vein enters the liver and breaks up again into veins of diminishing size, which ultimately join capillary-like vessels, termed sinusoids, in the liver (Fig. 1-17). A portal system is thus a system of vessels interposed between two capillary beds. Capillaries are microscopic vessels in the form of a network connecting the arterioles to the venules (Fig. 1-17). Sinusoids resemble capillaries in that they are thin-walled blood vessels, but they have an irregular cross diameter and are wider than capillaries. They are found in the bone marrow, the spleen, the liver, and some endocrine glands. In some areas of the body, principally the tips of the fingers and toes, direct connections occur between the arteries and veins without the intervention of capillaries. The sites of such connections are referred to as arteriovenous anastomoses (Fig. 1-17). Clinical Notes Diseases of Blood Vessels Diseases of blood vessels are common. The surface anatomy of the main arteries, especially those of the limbs, is discussed in the appropriate sections of this book. The collateral circulation of most large arteries should be understood, and a distinction should be made between anatomic end arteries and functional end arteries. All large arteries that cross over a joint are liable to be kinked during movements of the joint. However, the distal flow of blood is not interrupted because an adequate anastomosis is usually between branches of the artery that arise both proximal and distal to the joint. The alternative blood channels, which dilate under these circumstances, form the collateral circulation. Knowledge of the existence and position of such a circulation may be of vital importance should it be necessary to tie off a large artery that has been damaged by trauma or disease. Coronary arteries are functional end arteries, and if they become blocked by disease (coronary arterial occlusion is common), the cardiac muscle normally supplied by that artery will receive insufficient blood and undergo necrosis. Blockage of a large coronary artery results in the death of the patient. (See the clinical example at the beginning of this chapter.) P.19

Figure 1-16 General plan of the blood vascular system.

P.20

Figure 1-17 Different types of blood vessels and their methods of union. A. Anastomosis between the branches of the superior mesenteric artery. B. A capillary network and an arteriovenous anastomosis. C. Anatomic end artery and functional end artery. D. A portal system. E. Structure of the bicuspid valve in a vein.

Lymphatic System The lymphatic system consists of lymphatic tissues and lymphatic vessels (Fig. 1-18). Lymphatic tissues are a type of connective tissue that contains large numbers of lymphocytes. Lymphatic tissue is organized into the following organs or structures: the thymus, the lymph nodes, the spleen, and the lymphatic nodules. Lymphatic tissue is essential for the immunologic defenses of the body against bacteria and viruses. Lymphatic vessels are tubes that assist the cardiovascular system in the removal of tissue fluid from the tissue spaces of the body; the vessels then return the fluid to P.21
the blood. The lymphatic system is essentially a drainage system, and there is no circulation. Lymphatic vessels are found in all tissues and organs of the body except the central nervous system, the eyeball, the internal ear, the epidermis of the skin, the cartilage, and the bone. Lymph is the name given to tissue fluid once it has entered a lymphatic vessel. Lymph capillaries are a network of fine vessels that drain lymph from the tissues. The capillaries are in turn drained by small lymph vessels, which unite to form large lymph vessels. Lymph vessels have a beaded appearance because of the presence of numerous valves along their course. Before lymph is returned to the bloodstream, it passes through at least one lymph node and often through several. The lymph vessels that carry lymph to a lymph node are referred to as afferent vessels (Fig. 1-18); those that transport it away from a node are efferent vessels. The lymph reaches the bloodstream at the root of the neck by large lymph vessels called the right lymphatic duct and the thoracic duct (Fig. 1-18). Clinical Notes Disease of the Lymphatic System The lymphatic system is often deemphasized by anatomists on the grounds that it is difficult to see on a cadaver. However, it is of vital importance to medical personnel, since lymph nodes may swell as the result of metastases, or primary tumor. For this reason, the lymphatic drainage of all major organs of the body, including the skin, should be known. A patient may complain of a swelling produced by the enlargement of a lymph node. A physician must know the areas of the body that drain lymph to a particular node if he or she is to be able to find the primary site of the disease. Often the patient ignores the primary disease, which may be a small, painless cancer of the skin. Conversely, the patient may complain of a painful ulcer of the tongue, for example, and the physician must know the lymph drainage of the tongue to be able to determine whether the disease has spread beyond the limits of the tongue. Nervous System The nervous system is divided into two main parts: the central nervous system, which consists of the brain and spinal cord, and the peripheral nervous system, which consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves and their associated ganglia. Functionally, the nervous system can be further divided into the somatic nervous system, which controls voluntary activities, and the autonomic nervous system, which controls involuntary activities. The nervous system, together with the endocrine system, controls and integrates the activities of the different parts of the body. Central Nervous System The central nervous system is composed of large numbers of nerve cells and their processes, supported by specialized tissue called neuroglia. Neuron is the term given to the nerve cell and all its processes. The nerve cell has two types of processes, called dendrites and an axon. Dendrites are the short processes of the cell body; the axon is the longest process of the cell body (Fig. 1-19). The interior of the central nervous system is organized into gray and white matter. Gray matter consists of nerve cells embedded in neuroglia. White matter consists of nerve fibers (axons) embedded in neuroglia. Peripheral Nervous System The peripheral nervous system consists of the cranial and spinal nerves and their associated ganglia. On dissection, the cranial and spinal nerves are seen as grayish white cords. They are made up of bundles of nerve fibers (axons) supported by delicate areolar tissue. Cranial Nerves There are 12 pairs of cranial nerves that leave the brain and pass through foramina in the skull. All the nerves are distributed in the head and neck except the Xth (vagus), which also supplies structures in the thorax and abdomen. The cranial nerves are described in Chapter 11. Spinal Nerves A total of 31 pairs of spinal nerves leave the spinal cord and pass through intervertebral foramina in the vertebral column (Figs. 1-20 and 1-21). The spinal nerves are named according to the region of the vertebral column with which they are associated: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. Note that there are eight cervical nerves and only seven cervical vertebrae and that there is one coccygeal nerve and four coccygeal vertebrae. During development, the spinal cord grows in length more slowly than the vertebral column. In the adult, when growth ceases, the lower end of the spinal cord reaches inferiorly only as far as the lower border of the first lumbar vertebra. To accommodate for this disproportionate growth in length, the length of the roots increases progressively from above downward. In the upper cervical region, the spinal nerve roots are short and run almost horizontally, but the roots of the lumbar and sacral nerves below the level of the termination of the cord form a vertical bundle of nerves that resembles a horse’s tail and is called the cauda equina (Fig. 1-20). Each spinal nerve is connected to the spinal cord by two roots: the anterior root and the posterior root (Figs. 1-19 and 1-21). The anterior root consists of bundles of nerve fibers carrying nerve impulses away from the central nervous system (Fig. 1-21). Such nerve fibers are called efferent fibers. Those efferent fibers that go to skeletal muscle and cause them to contract are calledmotor fibers. Their cells of origin lie in the anterior gray horn of the spinal cord. The posterior root consists of bundles of nerve fibers that carry impulses to the central nervous system and are called afferent fibers (Fig. 1-19). Because these fibers are concerned with conveying information about sensations of P.22
touch, pain, temperature, and vibrations, they are called sensory fibers. The cell bodies of these nerve fibers are situated in a swelling on the posterior root called the posterior root ganglion (Figs. 1-19 and 1-21).

Figure 1-18 A. The thoracic duct and right lymphatic duct and their main tributaries. B. The areas of body drained into thoracic duct (clear) and right lymphatic duct (black). C. General structure of a lymph node. D. Lymph vessels and nodes of the upper limb.

At each intervertebral foramen, the anterior and posterior roots unite to form a spinal nerve (Fig. 1-21). Here, the motor and sensory fibers become mixed together, so that a spinal nerve is made up of a mixture of motor and sensory fibers (Fig. 1-19). On emerging from the foramen, the spinal nerve divides into a large anterior ramus and a smaller posterior ramus. The posterior ramus passes posteriorly around the vertebral column to supply the muscles and skin of the back (Figs. 1-19 and 1-21). The anterior ramus continues anteriorly to supply the muscles and skin over the anterolateral body wall and all the muscles and skin of the limbs. In addition to the anterior and posterior rami, spinal nerves give a small meningeal branch that supplies the vertebrae and the coverings of the spinal cord (the meninges). Thoracic spinal nerves also have branches, called rami communicantes, that are associated with the sympathetic part of the autonomic nervous system (see below). P.23

Figure 1-19 A. Multipolar motor neuron with connector neuron synapsing with it. B. Section through thoracic segment of spinal cord with spinal roots and posterior root ganglion. C. Cross section of thoracic segment of spinal cord showing roots, spinal nerve, and anterior and posterior rami and their branches.

Plexuses At the root of the limbs, the anterior rami join one another to form complicated nerve plexuses (Fig. 1-20). The cervical and brachial plexuses are found at the root of the upper limbs, and the lumbar and sacral plexuses are found at the root of the lower limbs. The classic division of the nervous system into central and peripheral parts is purely artificial and one of descriptive convenience because the processes of the neurons pass freely between the two. For example, a motor neuron located in the anterior gray horn of the first thoracic segment of the spinal cord gives rise to an axon that passes through the anterior root of the first thoracic nerve (Fig. 1-22), passes through the brachial plexus, travels down the arm and forearm in the ulnar nerve, and finally reaches the motor end plates on several muscle fibers of a small muscle of the hand—a total distance of about 3 ft (90 cm). To take another example: Consider the sensation of touch felt on the lateral side of the little toe. This area of skin P.24
is supplied by the first sacral segment of the spinal cord (S1). The fine terminal branches of the sensory axon, called dendrites, leave the sensory organs of the skin and unite to form the axon of the sensory nerve. The axon passes up the leg in the sural nerve (Fig. 1-22) and then in the tibial and sciatic nerves to the lumbosacral plexus. It then passes through the posterior root of the first sacral nerve to reach the cell body in the posterior root ganglion of the first sacral nerve. The central axon now enters the posterior white column of the spinal cord and passes up to the nucleus gracilis in the medulla oblongata—a total distance of about 5 ft (1.5 m). Thus, a single neuron extends from the little toe to the inside of the skull.

Figure 1-20 Brain, spinal cord, spinal nerves, and plexuses of limbs.

Both these examples illustrate the great length of a single neuron. Autonomic Nervous System The autonomic nervous system is the part of the nervous system concerned with the innervation of involuntary structures such as the heart, smooth muscle, and glands throughout the body and is distributed throughout the central and peripheral nervous system. The autonomic system may be divided into two parts—the sympathetic and the parasympathetic—and both parts have afferent and efferent nerve fibers. The activities of the sympathetic part of the autonomic system prepare the body for an emergency. It accelerates the heart rate, causes constriction of the peripheral blood vessels, and raises the blood pressure. The sympathetic part of the autonomic system brings about a redistribution of the blood so that it leaves the areas of the skin and intestine and becomes available to the brain, heart, and skeletal muscle. P.25
P.26
At the same time, it inhibits peristalsis of the intestinal tract and closes the sphincters.

Figure 1-21 The association between spinal cord, spinal nerves, and sympathetic trunks.
Figure 1-22 Two neurons that pass from the central to the peripheral nervous system. A. Afferent neuron that extends from the little toe to the brain. B. Efferent neuron that extends from the anterior gray horn of the first thoracic segment of spinal cord to the small muscle of the hand.

Clinical Notes Segmental Innervation of the Skin The area of skin supplied by a single spinal nerve, and therefore a single segment of the spinal cord, is called a dermatome. On the trunk, adjacent dermatomes overlap considerably; to produce a region of complete anesthesia, at least three contiguous spinal nerves must be sectioned. Dermatomal charts for the anterior and posterior surfaces of the body are shown in Figures 1-23 and 1-24. In the limbs, arrangement of the dermatomes is more complicated because of the embryologic changes that take place as the limbs grow out from the body wall. A physician should have a working knowledge of the segmental (dermatomal) innervation of skin, because with the help of a pin or a piece of cotton he or she can determine whether the sensory function of a particular spinal nerve or segment of the spinal cord is functioning normally. Segmental Innervation of Muscle Skeletal muscle also receives a segmental innervation. Most of these muscles are innervated by two, three, or four spinal nerves and therefore by the same number of segments of the spinal cord. To paralyze a muscle completely, it is thus necessary to section several spinal nerves or to destroy several segments of the spinal cord. Learning the segmental innervation of all the muscles of the body is an impossible task. Nevertheless, the segmental innervation of the following muscles should be known because they can be tested by eliciting simple muscle reflexes in the patient (Fig. 1-25):

  • Biceps brachii tendon reflex: C5 and 6 (flexion of the elbow joint by tapping the biceps tendon)
  • Triceps tendon reflex: C6, 7, and 8 (extension of the elbow joint by tapping the triceps tendon)
  • Brachioradialis tendon reflex: C5, 6, and 7 (supination of the radioulnar joints by tapping the insertion of the brachioradialis tendon)
  • Abdominal superficial reflexes (contraction of underlying abdominal muscles by stroking the skin): Upper abdominal skin T6 to 7, middle abdominal skin T8 to 9, and lower abdominal skin T10 to 12
  • Patellar tendon reflex (knee jerk): L2, 3, and 4 (extension of the knee joint on tapping the patellar tendon)
  • Achilles tendon reflex (ankle jerk): S1 and S2 (plantar flexion of the ankle joint on tapping the Achilles tendon)

The activities of the parasympathetic part of the autonomic system aim at conserving and restoring energy. They slow the heart rate, increase peristalsis of the intestine and glandular activity, and open the sphincters. The hypothalamus of the brain controls the autonomic nervous system and integrates the activities of the autonomic and neuroendocrine systems, thus preserving homeostasis in the body. Sympathetic System Efferent Fibers The gray matter of the spinal cord, from the first thoracic segment to the second lumbar segment, possesses a lateral horn, or column, in which are located the cell bodies of the sympathetic connector neurons (Fig. 1-26). The myelinated axons of these cells leave the spinal cord in the anterior nerve roots and then pass via the white rami communicantes to the paravertebral ganglia of the sympathetic trunk (Figs. 1-21, 1-26, and 1-27). The connector cell fibers are called preganglionic as they pass to a peripheral ganglion. Once the preganglionic fibers reach the ganglia in the sympathetic trunk, they may pass to the following destinations:

  • They may terminate in the ganglion they have entered by synapsing with an excitor cell in the ganglion (Fig. 1-26). A synapse can be defined as the site where two neurons come into close proximity but not into anatomic continuity. The gap between the two neurons is bridged by a neurotransmitter substance, acetylcholine. The axons of the excitor neurons leave the ganglion and are nonmyelinated. These postganglionic nerve fibers now pass to the thoracic spinal nerves as gray rami communicantes and are distributed in the branches of the spinal nerves to supply the smooth muscle in the walls of blood vessels, the sweat glands, and the arrector pili muscles of the skin.
  • Those fibers entering the ganglia of the sympathetic trunk high up in the thorax may travel up in the sympathetic trunk to the ganglia in the cervical region, where they synapse with excitor cells (Figs. 1-26 and 1-27). Here, again, the postganglionic nerve fibers leave the sympathetic trunk as gray rami communicantes, and most of them join the cervical spinal nerves. Many of the preganglionic fibers entering the lower part of the sympathetic trunk from the lower thoracic and upper two lumbar segments of the spinal cord travel down to ganglia in the lower lumbar and sacral regions, where they synapse with excitor cells (Fig. 1-27). The postganglionic fibers leave the sympathetic trunk as gray rami communicantes that join the lumbar, sacral, and coccygeal spinal nerves.
  • The preganglionic fibers may pass through the ganglia on the thoracic part of the sympathetic trunk without synapsing. These myelinated fibers form the three splanchnic nerves (Fig. 1-27). The greater splanchnic nerve arises from the fifth to the ninth thoracic ganglia, pierces the diaphragm, and synapses with excitor cells in the ganglia of the celiac plexus. The lesser splanchnic nerve arises P.27
    from the 10th and 11th ganglia, pierces the diaphragm, and synapses with excitor cells in the ganglia of the lower part of the celiac plexus. The lowest splanchnic nerve (when present) arises from the 12th thoracic ganglion, pierces the diaphragm, and synapses with excitor cells in the ganglia of the renal plexus. Splanchnic nerves are therefore composed of preganglionic fibers. The postganglionic fibers arise from the excitor cells in the peripheral plexuses previously noted and are distributed to the smooth muscle and glands of the viscera. A few preganglionic fibers traveling in the greater splanchnic nerve end directly on the cells of the suprarenal medulla. These medullary cells may be regarded as modified sympathetic excitor cells.
Figure 1-23 Dermatomes and distribution of cutaneous nerves on the anterior aspect of the body.

Sympathetic trunks are two ganglionated nerve trunks that extend the whole length of the vertebral column (Fig. 1-27). There are 3 ganglia in each trunk of the neck, 11 or 12 ganglia in the thorax, 4 or 5 ganglia in the lumbar region, and 4 or 5 ganglia in the pelvis. The two trunks lie close to the vertebral column and end below by joining together to form a single ganglion, the ganglion impar. Afferent Fibers The afferent myelinated nerve fibers travel from the viscera through the sympathetic ganglia without synapsing (Fig. 1-26). They enter the spinal nerve via the white rami communicantes and reach their cell bodies in the posterior root ganglion of the corresponding spinal nerve. The central axons then enter the spinal cord P.28
and may form the afferent component of a local reflex arc. Others may pass up to higher autonomic centers in the brain.

Figure 1-24 Dermatomes and distribution of cutaneous nerves on the posterior aspect of the body.

Parasympathetic System Efferent Fibers The connector cells of this part of the system are located in the brain and the sacral segments of the spinal cord (Fig. 1-27). Those in the brain form parts of the nuclei of origin of cranial nerves III, VII, IX, and X, and the axons emerge from the brain contained in the corresponding cranial nerves. The sacral connector cells are found in the gray matter of the second, third, and fourth sacral segments of the cord. These cells are not sufficiently numerous to form a lateral gray horn, as do the sympathetic connector cells in the thoracolumbar region. The myelinated axons leave the spinal cord in the anterior nerve roots of the corresponding spinal nerves. They then leave the sacral nerves and form the pelvic splanchnic nerves. All the efferent fibers described so far are preganglionic, and they synapse with excitor cells in peripheral ganglia, which are usually situated close to the viscera they innervate. The cranial preganglionic fibers relay in the ciliary, pterygopalatine, submandibular, and otic ganglia (Fig. 1-27). The preganglionic fibers in the pelvic splanchnic nerves relay in ganglia in the hypogastric P.29
plexuses or in the walls of the viscera. Characteristically, the postganglionic fibers are nonmyelinated and are relatively short compared with sympathetic postganglionic fibers.

Figure 1-25 Some important tendon reflexes used in medical practice.

Afferent Fibers The afferent myelinated fibers travel from the viscera to their cell bodies located either in the sensory ganglia of the cranial nerves or in the posterior root ganglia of the sacrospinal nerves. The central axons then enter the central nervous system and take part in the formation of local reflex arcs, or pass to higher centers of the autonomic nervous system. The afferent component of the autonomic system is identical to the afferent component of somatic nerves and forms part of the general afferent segment of the entire nervous system. The nerve endings in the autonomic afferent component may not be activated by such sensations as heat or P.30
touch but instead by stretch or lack of oxygen. Once the afferent fibers gain entrance to the spinal cord or brain, they are thought to travel alongside, or are mixed with, the somatic afferent fibers.

Figure 1-26 General arrangement of somatic part of nervous system (left) compared to autonomic part of nervous system (right).

Clinical Notes Clinical Modification of the Activities of the Autonomic Nervous System Many drugs and surgical procedures that can modify the activity of the autonomic nervous system are available. For example, drugs can be administered to lower the blood pressure by blocking sympathetic nerve endings and causing vasodilatation of peripheral blood vessels. In patients with severe arterial disease affecting the main arteries of the lower limb, the limb can sometimes be saved by sectioning the sympathetic innervation to the blood vessels. This produces a vasodilatation and enables an adequate amount of blood to flow through the collateral circulation, thus bypassing the obstruction. Mucous Membranes Mucous membrane is the name given to the lining of organs or passages that communicate with the surface of the body. A mucous membrane consists essentially of a layer of epithelium supported by a layer of connective tissue, the lamina propria. Smooth muscle, called the muscularis mucosa, is sometimes present in the connective tissue. A mucous membrane may or may not secrete mucus on its surface. Serous Membranes Serous membranes line the cavities of the trunk and are reflected onto the mobile viscera lying within these cavities (Fig. 1-28). They consist of a smooth layer of mesothelium supported by a thin layer of connective tissue. The serous membrane lining the wall of the cavity is referred to as the parietal layer, and that covering the viscera is called the visceral layer. The narrow, slitlike interval that separates these layers forms the pleural, pericardial, and peritoneal cavities and contains a small amount of serous liquid, the serous exudate. The serous exudate lubricates the surfaces of the membranes and allows the two layers to slide readily on each other. The mesenteries, omenta, and serous ligaments are described in other chapters of this book. The parietal layer of a serous membrane is developed from the somatopleure (inner cell layer of mesoderm) and is richly supplied by spinal nerves. It is therefore sensitive to all common sensations such as touch and pain. The visceral layer is developed from the splanchnopleure (inner cell layer of mesoderm) and is supplied by autonomic nerves. It is insensitive to touch and temperature but very sensitive to stretch. P.31

Figure 1-27 Efferent part of autonomic nervous system. Preganglionic parasympathetic fibers are shown in solid blue; postganglionic parasympathetic fibers, in interrupted blue. Preganglionic sympathetic fibers are shown in solid red; postganglionic sympathetic fibers, in interrupted red.
Figure 1-28 Arrangement of pleura within the thoracic cavity. Note that under normal conditions the pleural cavity is a slitlike space; the parietal and visceral layers of pleura are separated by a small amount of serous fluid.

Clinical Notes Mucous and Serous Membranes and Inflammatory Disease Mucous and serous membranes are common sites for inflammatory disease. For example, rhinitis, or the common cold, is an inflammation of the nasal mucous membrane, and pleurisy is an inflammation of the visceral and parietal layers of the pleura. P.32
Bone Bone is a living tissue capable of changing its structure as the result of the stresses to which it is subjected. Like other connective tissues, bone consists of cells, fibers, and matrix. It is hard because of the calcification of its extracellular matrix and possesses a degree of elasticity because of the presence of organic fibers. Bone has a protective function; the skull and vertebral column, for example, protect the brain and spinal cord from injury; the sternum and ribs protect the thoracic and upper abdominal viscera (Fig. 1-29). It serves as a lever, as seen in the long bones of the limbs, and as an important storage area for calcium salts. It houses and protects within its cavities the delicate blood-forming bone marrow.

Figure 1-29 The skeleton. A. Anterior view. B. Lateral view.

Bone exists in two forms: compact and cancellous. Compact bone appears as a solid mass; cancellous bone consists of a branching network of trabeculae (Fig. 1-30). The trabeculae are arranged in such a manner as to resist the stresses and strains to which the bone is exposed. Classification of Bones Bones may be classified regionally or according to their general shape. The regional classification is summarized in Table 1-2. Bones are grouped as follows based on their P.33
general shape: long bones, short bones, flat bones, irregular bones, and sesamoid bones.

Figure 1-30 Sections of different types of bones. A. Long bone (humerus).B. Irregular bone (calcaneum). C. Flat bone (two parietal bones separated by the sagittal suture). D. Sesamoid bone (patella). E. Note arrangement of trabeculae to act as struts to resist both compression and tension forces in the upper end of the femur.

Long Bones Long bones are found in the limbs (e.g., the humerus, femur, metacarpals, metatarsals, and phalanges). Their length is greater than their breadth. They have a tubular shaft, the diaphysis, and usually an epiphysis at each end. During the growing phase, the diaphysis is separated from the epiphysis by an epiphyseal cartilage. The part of the diaphysis that lies adjacent to the epiphyseal cartilage is called the metaphysis. The shaft has a central marrow cavity containing bone marrow. The outer part of the shaft is composed of compact bone that is covered by a connective tissue sheath, the periosteum. The ends of long bones are composed of cancellous bone surrounded by a thin layer of compact bone. The articular surfaces of the ends of the bones are covered by hyaline cartilage. Short Bones Short bones are found in the hand and foot (e.g., the scaphoid, lunate, talus, and calcaneum). They are roughly cuboidal in shape and are composed of cancellous bone surrounded by a thin layer of compact bone. Short bones are covered with periosteum, and the articular surfaces are covered by hyaline cartilage. Flat Bones Flat bones are found in the vault of the skull (e.g., the frontal and parietal bones). They are composed of thin inner and outer layers of compact bone, the tables, separated by a layer of cancellous bone, the diploë. The scapulae, although irregular, are included in this group. Irregular Bones Irregular bones include those not assigned to the previous groups (e.g., the bones of the skull, the vertebrae, and the pelvic bones). They are composed of a thin shell of P.34
compact bone with an interior made up of cancellous bone.

Table 1-2 Regional Classification of Bones
Region of Skeleton Number of Bones
Axial skeleton
    Skull
        Cranium 8
        Face 14
        Auditory ossicles 6
    Hyoid 1
    Vertebrae (including sacrum and coccyx) 26
    Sternum 1
    Ribs 24
Appendicular skeleton
    Shoulder girdles
        Clavicle 2
        Scapula 2
Upper extremities
    Humerus 2
    Radius 2
    Ulna 2
    Carpals 16
    Metacarpals 10
    Phalanges 28
Pelvic girdle
    Hip bone 2
Lower extremities
    Femur 2
    Patella 2
    Fibula 2
    Tibia 2
    Tarsals 14
    Metatarsals 10
    Phalanges 28
206

Sesamoid Bones Sesamoid bones are small nodules of bone that are found in certain tendons where they rub over bony surfaces. The greater part of a sesamoid bone is buried in the tendon, and the free surface is covered with cartilage. The largest sesamoid bone is the patella, which is located in the tendon of the quadriceps femoris. Other examples are found in the tendons of the flexor pollicis brevis and flexor hallucis brevis. The function of a sesamoid bone is to reduce friction on the tendon; it can also alter the direction of pull of a tendon. Surface Markings of Bones The surfaces of bones show various markings or irregularities. Where bands of fascia, ligaments, tendons, or aponeuroses are attached to bone, the surface is raised or roughened. These roughenings are not present at birth. They appear at puberty and become progressively more obvious during adult life. The pull of these fibrous structures causes the periosteum to be raised and new bone to be deposited beneath. In certain situations, the surface markings are large and are given special names. Some of the more important markings are summarized in Table 1-3. Bone Marrow Bone marrow occupies the marrow cavity in long and short bones and the interstices of the cancellous bone in flat and irregular bones. At birth, the marrow of all the bones of the body is red and hematopoietic. This blood-forming activity gradually lessens with age, and the red marrow is replaced by yellow marrow. At 7 years of age, yellow marrow begins to appear in the distal bones of the limbs. This replacement of marrow gradually moves proximally, so that by the time P.35
the person becomes an adult, red marrow is restricted to the bones of the skull, the vertebral column, the thoracic cage, the girdle bones, and the head of the humerus and femur.

Table 1-3 Surface Markings of Bones
Bone Marking Example
Linear elevation
Line Superior nuchal line of the occipital bone
Ridge The medial and lateral supracondylar ridges of the humerus
Crest The iliac crest of the hip bone
Rounded elevation
Tubercle Pubic tubercle
Protuberance External occipital protuberance
Tuberosity Greater and lesser tuberosities of the humerus
Malleolus Medial malleolus of the tibia, lateral malleolus of the fibula
Trochanter Greater and lesser trochanters of the femur
Sharp elevation
Spine or spinous process Ischial spine, spine of vertebra
Styloid process Styloid process of temporal bone
Expanded ends for articulation
Head Head of humerus, head of femur
Condyle (knucklelike process) Medial and lateral condyles of femur
Epicondyle (a prominence situated just above condyle) Medial and lateral epicondyles of femur
Small flat area for articulation
Facet Facet on head of rib for articulation with vertebral body
Depressions
Notch Greater sciatic notch of hip bone
Groove or sulcus Bicipital groove of humerus
Fossa Olecranon fossa of humerus, acetabular fossa of hip bone
Openings
Fissure Superior orbital fissure
Foramen Infraorbital foramen of the maxilla
Canal Carotid canal of temporal bone
Meatus External acoustic meatus of temporal bone

Clinical Notes Bone Fractures Immediately after a fracture, the patient suffers severe local pain and is not able to use the injured part. Deformity may be visible if the bone fragments have been displaced relative to each other. The degree of deformity and the directions taken by the bony fragments depend not only on the mechanism of injury but also on the pull of the muscles attached to the fragments. Ligamentous attachments also influence the deformity. In certain situations—for example, the ilium—fractures result in no deformity because the inner and outer surfaces of the bone are splinted by the extensive origins of muscles. In contrast, a fracture of the neck of the femur produces considerable displacement. The strong muscles of the thigh pull the distal fragment upward so that the leg is shortened. The very strong lateral rotators rotate the distal fragment laterally so that the foot points laterally. Fracture of a bone is accompanied by a considerable hemorrhage of blood between the bone ends and into the surrounding soft tissue. The blood vessels and the fibroblasts and osteoblasts from the periosteum and endosteum take part in the repair process. All bone surfaces, other than the articulating surfaces, are covered by a thick layer of fibrous tissue called the periosteum. The periosteum has an abundant vascular supply, and the cells on its deeper surface are osteogenic. The periosteum is particularly well united to bone at sites where muscles, tendons, and ligaments are attached to bone. Bundles of collagen fibers known as Sharpey’s fibers extend from the periosteum into the underlying bone. The periosteum receives a rich nerve supply and is very sensitive. Development of Bone Bone is developed by two processes: membranous and endochondral. In the first process the bone is developed directly from a connective tissue membrane; in the second, a cartilaginous model is first laid down and is later replaced by bone. For details of the cellular changes involved, a textbook of histology or embryology should be consulted. The bones of the vault of the skull are developed rapidly by the membranous method in the embryo, and this serves to protect the underlying developing brain. At birth, small areas of membrane persist between the bones. This is important clinically because it allows the bones a certain amount of mobility, so that the skull can undergo molding during its descent through the female genital passages. The long bones of the limbs are developed by endochondral ossification, which is a slow process that is not completed until the 18th to 20th year or even later. The center of bone formation found in the shaft of the bone is referred to as the diaphysis; the centers at the ends of the bone, as the epiphyses. The plate of cartilage at each end, lying between the epiphysis and diaphysis in a growing bone, is called the epiphyseal plate. The metaphysis is the part of the diaphysis that abuts onto the epiphyseal plate. Clinical Notes Rickets Rickets is a defective mineralization of the cartilage matrix in growing bones. This produces a condition in which the cartilage cells continue to grow, resulting in excess cartilage and a widening of the epiphyseal plates. The poorly mineralized cartilaginous matrix and the osteoid matrix are soft, and they bend under the stress of bearing weight. The resulting deformities include enlarged costochondral junctions, bowing of the long bones of the lower limbs, and bossing of the frontal bones of the skull. Deformities of the pelvis may also occur. Epiphyseal Plate Disorders Epiphyseal plate disorders affect only children and adolescents. The epiphyseal plate is the part of a growing bone concerned primarily with growth in length. Trauma, infection, diet, exercise, and endocrine disorders can disturb the growth of the hyaline cartilaginous plate, leading to deformity and loss of function. In the femur, for example, the proximal epiphysis can slip because of mechanical stress or excessive loads. The length of the limbs can increase excessively because of increased vascularity in the region of the epiphyseal plate secondary to infection or in the presence of tumors. Shortening of a limb can follow trauma to the epiphyseal plate resulting from a diminished blood supply to the cartilage. Cartilage Cartilage is a form of connective tissue in which the cells and fibers are embedded in a gel-like matrix, the latter being responsible for its firmness and resilience. Except on the exposed surfaces in joints, a fibrous membrane called the perichondrium covers the cartilage. There are three types of cartilage:

  • Hyaline cartilage has a high proportion of amorphous matrix that has the same refractive index as the fibers embedded in it. Throughout childhood and adolescence, it plays an important part in the growth in length of long bones (epiphyseal plates are composed of hyaline cartilage). It has a great resistance to wear and covers the articular surfaces of nearly all synovial joints. Hyaline cartilage is incapable of repair when fractured; the defect is filled with fibrous tissue.
  • Fibrocartilage has many collagen fibers embedded in a small amount of matrix and is found in the discs within P.36
    joints (e.g., the temporomandibular joint, sternoclavicular joint, and knee joint) and on the articular surfaces of the clavicle and mandible. Fibrocartilage, if damaged, repairs itself slowly in a manner similar to fibrous tissue elsewhere. Joint discs have a poor blood supply and therefore do not repair themselves when damaged.
  • Elastic cartilage possesses large numbers of elastic fibers embedded in matrix. As would be expected, it is flexible and is found in the auricle of the ear, the external auditory meatus, the auditory tube, and the epiglottis. Elastic cartilage, if damaged, repairs itself with fibrous tissue.

Hyaline cartilage and fibrocartilage tend to calcify or even ossify in later life. Effects of Sex, Race, and Age on Structure Descriptive anatomy tends to concentrate on a fixed descriptive form. Medical personnel must always remember that sexual and racial differences exist and that the body’s structure and function change as a person grows and ages. The adult male tends to be taller than the adult female and to have longer legs; his bones are bigger and heavier and his muscles are larger. He has less subcutaneous fat, which makes his appearance more angular. His larynx is larger and his vocal cords are longer so that his voice is deeper. He has a beard and coarse body hair. He possesses axillary and pubic hair, the latter extending to the region of the umbilicus. The adult female tends to be shorter than the adult male and to have smaller bones and less bulky muscles. She has more subcutaneous fat and fat accumulations in the breasts, buttocks, and thighs, giving her a more rounded appearance. Her head hair is finer and her skin is smoother in appearance. She has axillary and pubic hair, but the latter does not extend up to the umbilicus. The adult female has larger breasts and a wider pelvis than the male. She has a wider carrying angle at the elbow, which results in a greater lateral deviation of the forearm on the arm. Until the age of approximately 10 years, boys and girls grow at about the same rate. Around 12 years, boys often start to grow faster than girls, so that most males reach a greater adult height than females. Puberty begins between ages 10 and 14 in girls and between 12 and 15 in boys. In the girl at puberty, the breasts enlarge and the pelvis broadens. At the same time, a boy’s penis, testes, and scrotum enlarge; in both sexes, axillary and pubic hair appear. Racial differences may be seen in the color of the skin, hair, and eyes and in the shape and size of the eyes, nose, and lips. Africans and Scandinavians tend to be tall, as a result of long legs, whereas Asians tend to be short, with short legs. The heads of central Europeans and Asians also tend to be round and broad. After birth and during childhood, the bodily functions become progressively more efficient, reaching their maximum degree of efficiency during young adulthood. During late adulthood and old age, many bodily functions become less efficient. Clinical Notes Clinical Significance of Age on Structure The fact that the structure and function of the human body change with age may seem obvious, but it is often overlooked. A few examples of such changes are given here:

  • In the infant, the bones of the skull are more resilient than in the adult, and for this reason fractures of the skull are much more common in the adult than in the young child.
  • The liver is relatively much larger in the child than in the adult. In the infant, the lower margin of the liver extends inferiorly to a lower level than in the adult. This is an important consideration when making a diagnosis of hepatic enlargement.
  • The urinary bladder in the child cannot be accommodated entirely in the pelvis because of the small size of the pelvic cavity and thus is found in the lower part of the abdominal cavity. As the child grows, the pelvis enlarges and the bladder sinks down to become a true pelvic organ.
  • At birth, all bone marrow is of the red variety. With advancing age, the red marrow recedes up the bones of the limbs so that in the adult it is largely confined to the bones of the head, thorax, and abdomen.
  • Lymphatic tissues reach their maximum degree of development at puberty and thereafter atrophy, so the volume of lymphatic tissue in older persons is considerably reduced.

Radiographic Anatomy As a medical professional, you will be frequently called on to study normal and abnormal anatomy as seen on radiographs. Familiarity with normal radiographic anatomy permits one to recognize abnormalities quickly, such as fractures and tumors. The most common form of radiographic anatomy is studied on a radiograph (x-ray film), which provides a two-dimensional image of the interior of the body (Fig. 1-31). To produce such a radiograph, a single barrage of x-rays is passed through the body and exposes the film. Tissues of differing densities show up as images of differing densities on the radiograph (or fluorescent screen). A tissue that is relatively dense absorbs (stops) more x-rays than tissues that are less dense. A very dense tissue is said to be radiopaque, but a less dense tissue is said to be radiolucent. Bone is very dense and fat is moderately dense; other soft tissues are less dense. Unfortunately, an ordinary radiograph shows the images of the different organs superimposed onto a flat sheet of film. This overlap of organs and tissues often makes it difficult to visualize them. This problem is overcome to some extent by taking films at right angles to one another or by making stereoscopic films. Computed tomography (CT) scanning or computerized axial tomography (CAT) scanning permits the study P.37
of tissue slices so that tissues with minor differences in density can be recognized. CT scanning relies on the same physics as conventional x-rays but combines it with computer technology. A source of x-rays moves in an arc around the part of the body being studied and sends out a beam of x-rays. The x-rays, having passed through the region of the body, are collected by a special x-ray detector. Here, the x-rays are converted into electronic impulses that produce readings of the density of the tissue in a 1-cm slice of the body. From these readings, the computer is able to assemble a picture of the body called a CT scan, which can be viewed on a fluorescent screen and then photographed for later examination (Fig. 1-32). The procedure is safe and quick, lasts only a few seconds for each slice, and for most patients requires no sedation. Embryologic Notes Embryology and Clinical Anatomy Embryology provides a basis for understanding anatomy and an explanation of many of the congenital anomalies that are seen in clinical medicine. A very brief overview of the development of the embryo follows. Once the ovum has been fertilized by the spermatozoon, a single cell is formed, called the zygote. This undergoes a rapid succession of mitotic divisions with the formation of smaller cells. The centrally placed cells are called the inner cell mass and ultimately form the tissues of the embryo. The outer cells, called the outer cell mass, form the trophoblast, which plays an important role in the formation of the placenta and the fetal membranes. The cells that form the embryo become defined in the form of a bilaminar embryonic disc, composed of two germ layers. The upper layer is called the ectoderm and the lower layer, the entoderm. As growth proceeds, the embryonic disc becomes pear shaped, and a narrow streak appears on its dorsal surface formed of ectoderm, called the primitive streak. The further proliferation of the cells of the primitive streak forms a layer of cells that will extend between the ectoderm and the entoderm to form the third germ layer, called the mesoderm. Ectoderm Further thickening of the ectoderm gives rise to a plate of cells on the dorsal surface of the embryo called the neural plate. This plate sinks beneath the surface of the embryo to form the neural tube, which ultimately gives rise to the central nervous system. The remainder of the ectoderm forms the cornea, retina, and lens of the eye and the membranous labyrinth of the inner ear. The ectoderm also forms the epidermis of the skin; the nails and hair; the epithelial cells of the sebaceous, sweat, and mammary glands; the mucous membrane lining the mouth, nasal cavities, and paranasal sinuses; the enamel of the teeth; the pituitary gland and the alveoli and ducts of the parotid salivary glands; the mucous membrane of the lower half of the anal canal; and the terminal parts of the genital tract and the male urinary tract. Entoderm The entoderm eventually gives origin to the following structures: the epithelial lining of the alimentary tract from the mouth cavity down to halfway along the anal canal and the epithelium of the glands that develop from it—namely, the thyroid, parathyroid, thymus, liver, and pancreas—and the epithelial linings of the respiratory tract, pharyngotympanic tube and middle ear, urinary bladder, parts of the female and male urethras, greater vestibular glands, prostate gland, bulbourethral glands, and vagina. Mesoderm The mesoderm becomes differentiated into the paraxial, intermediate, and lateral mesoderms. The paraxial mesoderm is situated initially on either side of the midline of the embryo. It becomes segmented and forms the bones, cartilage, and ligaments of the vertebral column and part of the base of the skull. The lateral cells form the skeletal muscles of their own segment, and some of the cells migrate beneath the ectoderm and take part in the formation of the dermis and subcutaneous tissues of the skin. The intermediate mesoderm is a column of cells on either side of the embryo that is connected medially to the paraxial mesoderm and laterally to the lateral mesoderm. It gives rise to portions of the urogenital system. The lateral mesoderm splits into a somatic layer and a splanchnic layer associated with the ectoderm and the entoderm, respectively. It encloses a cavity within the embryo called the intraembryonic coelom. The coelom eventually forms the pericardial, pleural, and peritoneal cavities. The embryonic mesoderm, in addition, gives origin to smooth, voluntary, and cardiac muscle; all forms of connective tissue, including cartilage and bone; blood vessel walls and blood cells; lymph vessel walls and lymphoid tissue; the synovial membranes of joints and bursae; and the suprarenal cortex. When appropriate, a more detailed account of the development of different organs is given in the chapters to follow. The technique of magnetic resonance imaging (MRI) uses the magnetic properties of the hydrogen nucleus excited by radiofrequency radiation transmitted by a coil surrounding the body part. The excited hydrogen nuclei emit a signal that is detected as induced electric currents in a receiver coil. MRI is absolutely safe to the patient, and because it provides better differentiation between different soft tissues, its use can be more revealing than a CT scan. The reason for this is that some tissues contain more hydrogen in the form of water than do other tissues (Fig. 1-33). P.38

Figure 1-31 Posteroanterior radiograph of the thorax.

P.39

Figure 1-32 Computed tomography (CT) scans. A. The upper thorax at the level of the third thoracic vertebra. B. The upper abdomen at the level of the second lumbar vertebra. All CT scans are viewed from below. Thus, the right side of the body appears on the left side of the figure.

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Figure 1-33 Magnetic resonance imaging study of the head in a sagittal plane showing different parts of the brain.

Clinical Problem Solving Study the following case histories and select the best answer to the questions following them. A 45-year-old patient has a small, firm, mobile tumor on the dorsum of the right foot just proximal to the base of the big toe and superficial to the bones and the long extensor tendon but deep to the superficial fascia. 1. The following information concerning the tumor is correct except which? (a) It is situated on the upper surface of the foot close to the root of the big toe. (b) It is not attached to the first metatarsal bone. (c) It lies superficial to the deep fascia. (d) It lies superficial to the tendon of the extensor hallucis longus muscle. (e) It is attached to the capsule of the metatarsophalangeal joint of the big toe. View Answer1. E. The tumor is mobile and not fixed to the joint capsule. The tumor is a neurofibroma of a digital nerve. A 31-year-old woman has a history of poliomyelitis affecting the anterior horn cells of the lower thoracic and lumbar segments of the spinal cord on the left side. On examination, she has severe right lateral flexion deformity of the vertebral column. 2. The following statements are true about this case except which? (a) The virus of poliomyelitis attacks and destroys the motor anterior horn cells of the spinal cord. (b) The disease resulted in the paralysis of the muscles that normally laterally flex the vertebral column on the left side. (c) The muscles on the right side of the vertebral column are unapposed. (d) The right lateral flexion deformity is caused by the slow degeneration of the sensory nerve fibers originating from the vertebral muscles on the right side. View Answer2. D A 20-year-old woman severely sprains her left ankle while playing tennis. When she tries to move the foot so that the sole faces medially, she experiences severe pain. 3. What is the correct anatomic term for the movement of the foot that produces the pain? (a) Pronation (b) Inversion (c) Supination (d) Eversion View Answer3. B A 25-year-old man has a deep-seated abscess in the posterior part of the neck. 4. The following statements are correct concerning the abscess except which? (a) The abscess probably lies deep to the deep fascia. (b) The deep fascia determines the direction of spread of the abscess. (c) The abscess would be incised through a vertical skin incision. (d) The lines of cleavage are important when considering the direction of skin incisions. (e) The abscess would be incised through a horizontal skin incision. View Answer4. C. If possible, skin incisions in the neck are made in a horizontal direction to conform with the lines of cleavage. A 40-year-old workman received a severe burn on the anterior aspect of his right forearm. The area of the burn exceeded 4 in.2 (10 cm2). The greater part of the burn was superficial and extended only into the superficial part of the dermis. 5. In the superficially burned area, the epidermis cells would regenerate from the following sites except (a) the hair follicles. (b) the sebaceous glands. (c) the margins of the burn. (d) the deepest ends of the sweat glands. View Answer5. D 6. In a small area the burn penetrated as far as the superficial fascia; in this region, the epidermal cells would regenerate from the following sites except (a) the ends of the sweat glands that lie in the superficial fascia. (b) the margins of the burn. (c) the sebaceous glands. View Answer6. C In a 63-year-old man, an MRI of the lower thoracic region of the vertebral column reveals the presence of a tumor pressing on the lumbar segments of the spinal cord. He has a loss of sensation in the skin over the anterior surface of the left thigh and is unable to extend his left knee joint. Examination reveals that the muscles of the front of the left thigh have atrophied and have no tone and that the left knee jerk is absent. 7. The following statements concerning this patient are correct except which? (a) The tumor is interrupting the normal function of the efferent motor fibers of the spinal cord on the left side. (b) The quadriceps femoris muscles on the front of the left thigh are atrophied. (c) The loss of skin sensation is confined to the dermatomes L1, 2, 3, and 4. (d) The absence of the left knee jerk is because of involvement of the first lumbar spinal segment. (e) The loss of muscle tone is caused by interruption of a nervous reflex arc. View Answer7. D. The patellar tendon reflex (knee jerk) involves L2, 3, and 4 segments of the spinal cord. A woman recently took up employment in a factory. She is a machinist, and for 6 hours a day she has to move a lever repeatedly, which requires that she extend and flex her right wrist joint. At the end of the second week of her employment, she began to experience pain over the posterior surface of her wrist and noticed a swelling in the area. 8. The following statements concerning this patient are correct except which? (a) Extension of the wrist joint is brought about by several muscles that include the extensor digitorum muscle. (b) The wrist joint is diseased. (c) Repeated unaccustomed movements of tendons through their synovial sheaths can produce traumatic inflammation of the sheaths. (d) The diagnosis is traumatic tenosynovitis of the long tendons of the extensor digitorum muscle. View Answer8. B A 19-year-old boy was suspected of having leukemia. It was decided to confirm the diagnosis by performing a bone marrow biopsy. 9. The following statements concerning this procedure are correct except which? (a) The biopsy was taken from the lower end of the tibia. (b) Red bone marrow specimens can be obtained from the sternum or the iliac crests. (c) At birth, the marrow of all bones of the body is red and hematopoietic. (d) The blood-forming activity of bone marrow in many long bones gradually lessens with age, and the red marrow is gradually replaced by yellow marrow. View Answer9. A. In a 19-year-old boy, the bone marrow at the lower end of the tibia is yellow. A 22-year-old woman had a severe infection under the lateral edge of the nail of her right index finger. On examination, a series of red lines were seen to extend up the back of the hand and around to the front of the forearm and arm, up to the armpit. 10. The following statements concerning this patient are probably correct except which? (a) Palpation of the right armpit revealed the presence of several tender enlarged lymph nodes (lymphadenitis). (b) The red lines were caused by the superficial lymphatic vessels in the arm, which were red and inflamed (lymphangitis) and could be seen through the skin. (c) Lymph from the right arm entered the bloodstream through the thoracic duct. (d) Infected lymph entered the lymphatic capillaries from the tissue spaces. View Answer10. C. Lymph from the right upper limb enters the bloodstream through the right lymphatic duct. Review Questions Completion Questions Select the phrase that best completes each statement. 1. A patient who is standing in the anatomic position is (a) facing laterally. (b) has the palms of the hands directed medially. (c) has the ankles several inches apart. (d) is standing on his or her toes. (e) has the upper limbs by the sides of the trunk. View Answer1. E 2. A patient is performing the movement of flexion of the hip joint when she (a) moves the lower limb away from the midline in the coronal plane. (b) moves the lower limb posteriorly in the paramedian plane. (c) moves the lower limb anteriorly in the paramedian plane. (d) rotates the lower limb so that the anterior surface faces medially. (e) moves the lower limb toward the median sagittal plane. View Answer2. C Matching Questions Match each structure listed below with a structure or occurrence with which it is most closely associated. Each lettered answer may be used more than once. 3. Superficial fascia 4. Deep fascia 5. Skeletal muscle (a) Divides up interior of limbs into compartments (b) Adipose tissue (c) Tendon spindles (d) None of the above View Answer3. B 4. A 5. C For each joint listed below, indicate with which type of movement it is associated. 6. Sternoclavicular joint 7. Superior radioulnar joint 8. Ankle joint (a) Flexion (b) Gliding (c) Both A and B (d) Neither A nor B View Answer6. B 7. D 8. A For each joint listed below, give the most appropriate classification. 9. Joints between vertebral bodies 10. Inferior tibiofibular joint 11. Sutures between bones of vault of skull 12. Wrist joint (a) Synovial joint (b) Cartilaginous (c) Fibrous (d) None of the above View Answer9. B 10. C 11. C 12. A For each type of synovial joint listed below, give an appropriate example from the list of joints. 13. Hinge joint 14. Condyloid joint 15. Ball-and-socket joint 16. Saddle joint (a) Metacarpophalangeal joint of index finger (b) Shoulder joint (c) Wrist joint (d) Carpometacarpal joint of the thumb (e) None of the above View Answer13. E 14. A 15. B 16. D For each type of muscle action listed below, select the most appropriate definition. 17. Prime mover 18. Fixator 19. Synergist 20. Antagonist (a) A muscle that contracts isometrically to stabilize the origin of another muscle (b) A muscle that opposes the action of a flexor muscle (c) A muscle that is chiefly responsible for a particular movement (d) A muscle that prevents unwanted movements in an intermediate joint so that another muscle can cross that joint and act primarily on a distal joint (e) A muscle that opposes the action of a prime mover View Answer17. C 18. A 19. D 20. E For each type of blood vessel listed below, select an appropriate definition. 21. Arteriole 22. Portal vein 23. Anatomic end artery 24. Venule (a) A vessel that connects two capillary beds (b) A vessel whose terminal branches do not anastomose with branches or arteries supplying adjacent areas (c) A vessel that connects large veins to capillaries (d) An artery <0.1 mm in diameter (e) A thin-walled vessel that has an irregular cross diameter View Answer21. D 22. A 23. B 24. C For each of the lymphatic structures listed below, select an appropriate structure or function. 25. Lymph capillary 26. Thoracic duct 27. Right lymphatic duct 28. Lymph node (a) Present in the central nervous system (b) Drains lymph directly from the tissues (c) Contains lymphatic tissue and has both afferent and efferent vessels (d) Drains lymph from the right side of the head and neck, the right upper limb, and the right side of the thorax (e) Drains lymph from the right side of the abdomen View Answer25. B 26. E 27. D 28. C Multiple-Choice Questions Directions: Read the case histories and select the best answer to the question following them. The surgical notes of a patient state that she had a right infraumbilical paramedian incision through the skin of the anterior abdominal wall. 29. Where exactly was this incision made? (a) In the midline below the umbilicus (b) In the midline above the umbilicus (c) To the right of the midline above the umbilicus (d) To the right of the midline below the umbilicus (e) Just below the xiphoid process in the midline View Answer29. D After an attack of pericapsulitis of the left shoulder joint, a patient finds that a particular movement of the joint is restricted. 30. Which of the joint movements is restricted and by how much? (a) Abduction is limited to 30°. (b) Lateral rotation is limited to 45°. (c) Medial rotation is limited to 55°. (d) Flexion is limited to 90°. (e) Extension is limited to 45°. View Answer30. A

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