The Skin

Photomicrograph of the skin. The staining of this cross section of skin clearly shows the red superficial epidermis and the bluish dermis below it. This photograph has been cropped; the dermis is actually quite thick in comparison to the epidermis. (Ed Reschke. Barbara Cousins.)

Lines of Stress

Cleavage lines. A, If an incision "cuts across" cleavage lines (Langer’s lines), stress tends to pull the cut edges apart and may retard healing. B, Surgical incisions parallel to cleavage lines are subjected to less stress and tend to heal more rapidly.

Color changes in a bruise.

Color changes in a bruise. In this light-skinned individual, different colors appear in the skin as hemoglobin becomes unoxygenated and turns bluish (see Figure 6-12) and perhaps even black as the blood clots. As macrophages consume the hemoglobin, it is broken down into brownish, greenish, and yellowish pigments—sometimes producing a rainbow of skin colors. (From McCance K, Huether S: Pathophysiology, ed 5, St Louis, 2005, Mosby.)

Male pattern baldness.

An x linked gene.

Tinea infection

Tinea infection (ringworm). Note that the lesions heal in the center, with inflamed rings left on the skin’s surface. (From Shah B, Laude T: Atlas of pediatric clinical diagnosis, Philadelphia, 2000, Saunders.)

Classification of burns.

Classification of burns. Partial-thickness burns include first- and second-degree burns. Full-thickness burns include third-degree burns. Fourth-degree burns involve tissues under the skin, such as muscle or bone.

Structure of the Skin

Compact and cancellous bone in a flat bone.

Compact and cancellous bone in a flat bone. A, Section of a flat bone. (See also Figure 7-4.) Outer layers of compact bone surround cancellous bone. Note the fine structure of compact (B) and cancellous (C) bone. (B: Dennis Strete.)

Endochondral bone formation.

Endochondral bone formation. A, Cartilage model. B, Subperiosteal bone collar formation. C, Development of the primary ossification center and entrance of a blood vessel. D, Prominent medullary cavity with thickening and lengthening of the collar. E, Development of secondary ossification centers in epiphyseal cartilage. F, Enlargement of secondary ossification centers, with bone growth proceeding toward the diaphysis from each end. G, With cessation of bone growth, the lower, then upper epiphyseal plates disappear (only the epiphyseal lines remain).

Bone remodeling.

Bone remodeling. Bone formation on the outside of the shaft coupled with bone reabsorption on the inside increases the bone’s diameter. Endochondral growth during bone remodeling increases the length of the diaphyses and causes the epiphysis to enlarge.

Skeleton. A Anterior view.

Skeleton. A Anterior view.

Left half of the skull viewed from within.

Bones of the skull.

Bones of the skull. G, Vomer. G1, Anterior view; G2, lateral view.

Bones of the nasal cavity.

Bones of the nasal cavity.

Vertebrae.

Vertebrae. E, Lateral and superior views of a thoracic vertebra, T10. F, Lateral and superior views of a lumbar vertebra, L3. (From Gosling J, Harris P, Whitmore I, Willan P: Human anatomy, ed 4, Philadelphia, 2002, Mosby.)

Bones of the arm (right arm, posterior view)

Bones of the arm (right arm, posterior view). A, Humerus (upper part of the arm). B, Radius and ulna (forearm). C, Elbow joint, showing how the distal end of the humerus joins the proximal ends of the radius and ulna. (The inset shows the relative position of the right arm bones within the entire skeleton.) (C: Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

Arches of the foot.

Arches of the foot. A, Longitudinal arch. The medial portion is formed by the calcaneus, talus, navicular, cuneiforms, and three metatarsal bones; the lateral portion is formed by the calcaneus, cuboid, and two lateral metatarsal bones. B, "Flatfoot" results when the tendons and ligaments attached to the tarsal bones are weakened. Downward pressure by the weight of the body gradually flattens out the normal arch of the bones. The photo shows the clinical appearance of a flatfoot. C, Transverse arch in the metatarsal region of the left foot. D, High heels throw the weight forward and cause the heads of the metatarsal bones to bear most of the body's weight. (Arrows show direction of force.) (From Yvonne Wylie Walston. From Seidel HM, Ball JW, Dains JE, Benedict GW: Mosby's guide to physical examination, ed 5, St Louis, 2003, Mosby.)

Fibrous joints

Fibrous joints. Examples of the types of fibrous joints.

Joints of the wrist.

Joints of the wrist. A, Coronal section of the hand showing the joints of the wrist. Note that the thumb and little finger are not in the plane of section. B, Radiograph of an adolescent hand and wrist. Note that the epiphyseal plates are present. C, Major synovial spaces of the wrist: 1, proximal; 2, intermediate; 3, distal. (A-B: From Gosling J, Harris P, Whitmore I, Willan P: Human anatomy, ed 4, Philadelphia, 2002, Mosby. C: From Heylings D, Spence R, Kelly B: Integrated anatomy, Edinburgh, 2007, Churchill Livingstone.)

Vertebrae.

Vertebrae. Sagittal section of vertebrae showing normal (A) and herniated (B) disks.

Movements and ROM of the shoulder.

Movements and ROM of the shoulder. A, Forward flexion, extension (back to the anatomical position of 0 degrees), and backward hyperextension up to 50 degrees. B, Abduction and adduction. (From Barkauskas V, Baumann L, Stoltenberg-Allen K, Darling-Fisher C: Health and physical assessment, ed 2, St Louis, 1998, Mosby.)

Movements and ROM of the foot and ankle.

Movements and ROM of the foot and ankle. A, Dorsiflexion and plantar flexion. B, Inversion and eversion. C, Abduction and adduction.

Sports and Fitness. Knee arthrogram.

Sports and Fitness. Knee arthrogram A, Normal medial meniscus. Spot film showing the normal triangular shape of the meniscus (arrows). B, Linear tear of the medial meniscus.

Muscle actions.

Muscle actions. A, The flexor muscle (biceps brachii) is the prime mover in flexing the elbow. The extensor muscle (triceps brachii) is the antagonist, which in this case must relax to permit easy flexion of the elbow. The pronator teres muscle acts as a synergist by also flexing the elbow. B, Here the biceps brachii is again the prime mover of flexion of the elbow. The pronator teres muscle acts as a synergist by also flexing the elbow. To prevent the biceps from also moving the shoulder while straining against a heavy weight, the posterior portion of the deltoid muscle tenses to stabilize the shoulder joint—thus acting as a fixator muscle in this action. (Adapted from Muscolino J: Kinesiology, St Louis, 2006, Mosby.)

Muscles of mastication.

Muscles of mastication. A, Muscles of the tongue and pharynx. B, Right lateral dissection view showing the insertion of the temporalis muscle on the mandible—the masseter muscle is cut and part of the zygomatic arch has been removed. C, View of the pterygoids in a posterior dissection view. D, Lateral and medial pterygoid muscles viewed from the right side after removal of the zygomatic arch.

Muscles of the back.

Muscles of the back. B, Deep muscle dissection of the back—posterior view. The superficial and intermediate muscles have been removed. The muscles in the gluteal region have been removed to expose the pelvic insertion of the multifidus.

Muscles acting on the forearm.

Muscles acting on the forearm. A, Lateral view of the right shoulder and arm. B, Anterior view of the right shoulder and arm (deep). The deltoid and pectoralis major muscles have been removed to reveal deeper structures.

Cross sections (proximal to distal) through the lower extremity.

Cross sections (proximal to distal) through the lower extremity. A, Section through the middle of the femur. B, Section about 4 cm above the adductor tubercle of the femur. C, Section about 10 cm distal to the knee joint. D, Section about 6 cm above the medial malleolus. In each section you are viewing the superior (proximal) aspect of the specimen.

Superficial muscles of the leg. A, Anterior view. B, Posterior view. C, Lateral view.

Unique features of the skeletal muscle cell.

Unique features of the skeletal muscle cell. Notice especially the T tubules, which are extensions of the plasma membrane, or sarcolemma, and the sarcoplasmic reticulum (SR), a type of smooth endoplasmic reticulum that forms networks of tubular canals and sacs containing stored calcium ions. A triad is a triplet of adjacent tubules: a terminal (end) sac of the SR, a T tubule, and another terminal sac of the SR.

Effects of excitation on a muscle fiber.

Effects of excitation on a muscle fiber. Excitation of the sarcolemma by a nerve impulse initiates an impulse in the sarcolemma. The impulse travels across the sarcolemma and through the T tubules, where it triggers adjacent sacs of the sarcoplasmic reticulum to release a flood of calcium ions (Ca++) into the sarcoplasm. Ca++ is then free to bind to troponin molecules in the thin filaments. This binding, in turn, initiates the chemical reactions that produce a contraction.

Energy sources for muscle contraction.

Energy sources for muscle contraction. A, The basic structure of two high-energy molecules in the sarcoplasm: adenosine triphosphate (ATP) and creatine phosphate (CP). B, This diagram shows how energy released during the catabolism of nutrients can be transferred to the high-energy bonds of ATP directly or, instead, stored temporarily in the high-energy bond of CP. During contraction, ATP is hydrolyzed and the energy of the broken bond is transferred to a myosin head.

The twitch contraction.

The twitch contraction. Three distinct phases are apparent: (1) the latent period, (2) the contraction phase, and (3) the relaxation phase.

Factors that influence the strength of muscle contraction.

Muscle strain.

Muscle strain. Severe strain of the biceps brachii muscle. In a severe muscle strain, a muscle may break in two pieces and result in a visible gap in muscle tissue under the skin. Notice how the broken ends of the muscle reflexively contract (spasm) to form a knot of tissue. (Courtesy Rob Williams, from Booher JM, Thibodeau GA: Athletic injury assessment, ed 2, St Louis, 1989, Mosby.)

Effects of Exercise on Skeletal Muscles.

Effects of Exercise on Skeletal Muscles. B, Effects of aerobic training. The graph shows that aerobic training increases the metabolic condition of muscles mainly by increasing levels of enzymes and the availability of oxygen. Only moderate increases in muscle fiber size occur.

Skin Structure

Diagram of skin structure. A, Thick skin, found on surfaces of the palms and soles of the feet. B, Thin skin, found on most surface areas of the body. In each diagram, the epidermis is raised at one corner to reveal the papillae of the dermis.

Melanin

Melanin production. Melanin is produced by melanocytes in the stratum basale. Melanocytes have long projections that reach between the keratinocytes and release packets of pigment called melanosomes. By endocytosis, the melanosomes are brought into the keratinocytes, where they are arranged as a cap over the nucleus—protecting it from UV radiation from above.

Vitamin D production.

Vitamin D production. The essential first step in producing the active form of vitamin D in the body occurs in the presence of ultraviolet (UV) light in the skin.

Structure of nails.

Structure of nails. A, Fingernail viewed from above. B, Sagittal section of a fingernail and associated structures. (Courtesy Christine Olekyk.)

Decubitus ulcer.

Decubitus ulcer. The skin forms craterlike lesions when the blood supply is diminished and skin tissue cannot be maintained in the area of reduced blood flow. (From Potter P, Perry A: Basic nursing: essentials for practice, ed 5, St Louis, 2003, Mosby.)

Vitiligo.

The skeleton.

Orientation of trabeculae.

Orientation of trabeculae. Longitudinal section of a long bone showing trabeculae oriented along lines of stress.

Fetal ossification centers.

Fetal ossification centers. Photograph of a specially prepared fetal hand specimen showing primary ossification centers in the bones of the hand (metacarpal bones) and fingers (phalanges). Note that none of the wrist (carpal) bones show any evidence of ossification. (From Williams P: Gray’s anatomy, ed 38, Philadelphia, 1996, Churchill Livingstone.)

Primary osteon formation.

Primary osteon formation. First, a tubelike passage in the woven bone surrounding a blood vessel is demineralized by osteoblasts. Osteoblasts then begin laying down one layer (lamella) after another along the endosteal lining of the tube. As layers build up, they eventually fill most of the demineralized tube—thus forming the concentric lamellae around a central canal that characterize an osteon.

Skeleton. B, Posterior view. C, Lateral view.

Skeleton. B, Posterior view. C, Lateral view.

Bones of the left orbit and signs of fracture.

Bones of the left orbit and signs of fracture. A, Skull showing an area of enlargement. B, Diagram showing detail of the orbital bones.

Bones of the skull.

Bones of the skull. H, Right maxilla. H1, Medial view; H2, lateral view.

Skull at birth.

Skull at birth. A, Skull showing an area of enlargement. B, Diagram showing detail of the orbital bones. C, Viewed from behind. D, Viewed from above. (B-D: From Abrahams P, Marks S, Hutchings R: McMinn's color atlas of human anatomy, ed 5, Philadelphia, 2003, Mosby.)

Vertebrae.

Vertebrae. G, Lumbar vertebra L5 and the upper portion of the sacrum in an expanded anterior view. H, Oblique view of the sacrum, coccyx, and right hip bone. (From Gosling J, Harris P, Whitmore I, Willan P: Human anatomy, ed 4, Philadelphia, 2002, Mosby.)

Bones of the hand and wrist.

Bones of the hand and wrist. A, Dorsal view of the right hand and wrist. B, Palmar view of the right hand and wrist. (Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

Comparison of the bony pelvis of the male and female skeletons.

Comparison of the bony pelvis of the male and female skeletons. A and C, Diagrams showing components of the bony pelvis of the male and female. B and D, Photographs showing the bony pelvis of the male and female from in front and above. (B-D: From Abrahams P, Marks S, Hutchings R: McMinn's color atlas of human anatomy, ed 5, Philadelphia, 2003, Mosby.)

Cartilaginous joints

Cartilaginous joints. Examples of the types of cartilaginous joints.

Joints of the hand and fingers.

Joints of the hand and fingers. Radiograph of an adult hand shows the absence of epiphyseal plates. All the phalanges and metacarpal bones are easily seen. The inset shows a dissected specimen in a coronal section through the second metacarpophalangeal joint. The collateral ligaments are simply thickenings of the walls of the joint capsule. (From Gosling J, Harris P, Whitmore I, Willan P: Human anatomy, ed 4, Philadelphia, 2002, Mosby.)

Vertebrae and their ligaments.

Vertebrae and their ligaments. Sagittal section of two lumbar vertebrae and their ligaments.

ROM of elbow.

Movements and ROM of the elbow. A, Flexion and extension of the elbow. B, Supination and pronation. (From Barkauskas V, Baumann L, Stoltenberg-Allen K, Darling-Fisher C: Health and physical assessment, ed 2, St Louis, 1998, Mosby.)

Olecranon bursitis.

Olecranon bursitis. Pain, inflammation, and swelling of the bursa may limit motion, although the elbow joint itself may not be affected. (From Seidel HM, Ball JW, Dains JE, Benedict GW: Mosby's guide to physical examination, ed 5, St Louis, 2003, Mosby.)

Sports and Fitness. Joint replacement.

Lever classes.

Lever classes. A, Class I: fulcrum (F) between the load (L) and force or pull (P). B, Class II: load (L) between the fulcrum (F) and force or pull (P). C, Class III: force or pull (P) between the fulcrum (F) and the load (L). The lever rod is yellow in each.

Muscles that move the head. Posterior view of muscles of the neck and the back.

Muscles of the pelvic floor. A, Male, inferior view. B, Female, inferior view.

Muscles acting on the forearm.

Muscles acting on the forearm. A, Biceps brachii. B, Coracobrachialis and pronator teres. C, Triceps brachii. D, Brachialis. O, Origin; I, insertion.

Muscles of the anterior aspect of the thigh.

Muscles of the anterior aspect of the thigh. A, Anterior view of the right thigh. B, Adductor region of the right thigh. The tensor fasciae latae, sartorius, and quadriceps muscles have been removed.

Intrinsic muscles of the foot. Inferior (plantar) view.

Storage and release of calcium ions.

Storage and release of calcium ions. At rest (left), calcium ion pumps in the sarcoplasmic reticulum (SR) membrane actively pull Ca++ into the SR—thus creating a concentration gradient with very little Ca++ left in the sarcoplasm. Note that the Ca++ is sequestered by protein filaments (calsequestrin) in "bunches" just inside the closed Ca++ channels. When the fiber is stimulated (right), an electrical impulse travels from the sarcolemma and down the T tubule, where the voltage fluctuation triggers the opening of voltage-gated calcium channels. This allows passive diffusion of the Ca++ inside the SR out to the sarcoplasm, where it will trigger the contraction process. Almost immediately after stimulation, the calcium channels close and the Ca++ is once again pumped into the sacs of the SR (left). ATP, Adenosine triphosphate.

The molecular basis of muscle contraction.

Blood supply of muscle fibers.

Blood supply of muscle fibers. Tiny "exchange" vessels called capillaries branch out longitudinally (L) from small arteries (arrow) to form a network that supplies muscle fibers with glucose and oxygen and removes carbon dioxide and lactic acid. In this micrograph, the muscle fibers appear translucent and the blood vessels appear reddish. (From Lodish H: Molecular cell biology, ed 4, New York, 2000, WH Freeman.)

Myograms

Myograms of various types of muscle contractions. A, A single twitch contraction. B, The treppe phenomenon, or "staircase effect," is a steplike increase in the force of contraction over the first few in a series of twitches. C, Incomplete tetanus occurs when a rapid succession of stimuli produces "twitches" that seem to add together (wave summation) to produce a rather sustained contraction. D, Complete tetanus is a smoother sustained contraction produced by the summation of "twitches" that occur so close together that the muscle cannot relax at all.

Isotonic and isometric contraction.

Isotonic and isometric contraction. A, In isotonic contraction the muscle shortens and produces movement. Concentric contractions occur when the muscle shortens during the movement. Eccentric contractions occur when the contracting muscle lengthens. B, In isometric contraction the muscle pulls forcefully against a load but does not shorten because it cannot overcome the resistance.

A More Detailed Look at the Sarcomere.

Thin Skin

Thick and thin skin. A, The surface of thick skin is hairless and features regular, deep sulci and friction ridges, which form the "prints" of the palmar and plantar surfaces of the hands and feet. B, The surface of thin skin features irregular sulci (grooves) and hairs. (Copyright Kevin Patton, Lion Den Inc, Weldon Spring, MO.)

Skin Color

How genes affect skin color. Genes determine an individual’s basic skin color by controlling the amount and type of melanin synthesized and deposited in the epidermis. However, as the diagram shows, other factors may modify the basic skin color.

The skin as a thermoregulatory organ.

The skin as a thermoregulatory organ. When homeostasis requires that the body conserve heat, blood flow in the warm organs of the body’s core increases. A, When heat must be lost to maintain stability of the internal environment, flow of warm blood to the skin increases. B, Heat can be lost from the blood and skin by means of radiation, conduction, convection, and evaporation. The head, hands, and feet are major areas of heat loss.

Pigmented nails.

Pigmented nails. In light-skinned individuals, the nail bed is usually free of pigmentation. In very dark-skinned individuals, yellowish or brown pigmented bands (seen in the photograph) are common. (From Habif TP: Clinical dermatology, ed 4, St Louis, Mosby, 2004.)

Psoriasis.

Psoriasis. Inflammation and scaling are characteristic of this skin disorder. (From James WD, Berger TG, Elston DM: Andrew’s diseases of the skin: clinical dermatology, ed 10, London, 2000, Saunders.)

Blisters

Vesicular inflammation

Types of bones.

Types of bones. Examples of bone types include A, long bones (humerus); B, short bones (carpal bone); C, irregular bones (vertebra); D, flat bones (sternum); and E, sesamoid bones (patella and sesamoid of thumb).

Osteoblasts and Osteoclasts

Bone-forming and bone-eroding cells. Note the large multinucleate osteoclast cell (Oc) dissolving bone on the upper surface of a developing branch of bone while smaller osteoblast cells (Ob) on the undersurface of the bone are secreting new osteoid. (From Williams P: Gray’s anatomy, ed 38, Philadelphia, 1996, Churchill Livingstone.)

Endochondral ossification of the hand and wrist.

Endochondral ossification of the hand and wrist. Radiographs showing increasing numbers of ossification centers becoming visible in the wrist with increasing age. (From Zitelli B, Davis H: Atlas of pediatric physical diagnosis, ed 4, Philadelphia, Mosby, 2002.)

Bone fracture healing.

Bone fracture healing. A, Fracture of the femur. B, Formation of a fracture hematoma. C, Formation of internal and external bony callus. D, Bone remodeling complete.

Anterior view of the skull. (Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

Anterior view of the skull. (Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

Bones of the skull.

Bones of the skull. A, Right parietal bone viewed from the lateral side. B, Right temporal bone viewed from the lateral side.

Bones of the skull.

Bones of the skull. I, Right zygomatic bone viewed from the lateral side. J, Right palatine bone. J1, Medial view; J2, anterior view.

Hyoid bone

Hyoid bone. The photo insert (radiograph) shows the relationship of the hyoid bone to the base of the skull and cervical spine. Note that the hyoid does not articulate with any other bony structure.

Thoracic cage

Thoracic cage. Note the costal cartilages and their articulations with the body of the sternum.

The female pelvis.

The female pelvis. A, Pelvis viewed from above. Note that the brim of the true pelvis (dotted line) marks the boundary between the superior false pelvis (pelvis major) and the inferior true pelvis (pelvis minor). B and C, Pelvis viewed from below. A comparison of the male pelvis and female pelvis is shown in Figure 8-26. (C: Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

Bone fractures.

Bone fractures. A, Open. B, Closed. C, Incomplete and complete. D, Linear, transverse, and oblique.

Structure of synovial joints.

Structure of synovial joints. A, Artist's interpretation (composite drawing) of a typical synovial joint. B, Dissection photo showing the articular surface of a typical synovial joint—the distal radiocarpal joint (the joint capsule has been cut). See pp. 271-272 for a description of this joint. (B: From Gosling J, Harris P, Whitmore I, Willan P: Human anatomy, ed 4, Philadelphia, 2002, Mosby.)

The hip joint.

The hip joint. A, Artist's diagram, and B, dissection photo (anterior views). C, Artist's diagram, and D, dissection photo (frontal section). (B-D: Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

The Goniometer.

Use of a goniometer. Using a goniometer to measure ROM at the elbow. (From Barkauskas V, Baumann L, Stoltenberg-Allen K, Darling-Fisher C: Health and physical assessment, ed 2, St Louis, 1998, Mosby.)

ROM of hand and wrist.

Movements and ROM of hand and wrist. A, Metacarpophalangeal flexion and hyperextension. B, Wrist radial and ulnar movement. C, Wrist flexion and hyperextension. D, Finger abduction and adduction. (From Seidel HM, Ball JW, Dains JE, Benedict GW: Mosby's guide to physical examination, ed 5, St Louis

Types of arthritis.

Types of arthritis. A, Osteoarthritis. Note Heberden nodes (H) on the distal interphalangeal joints and Bouchard nodes (B) on the proximal interphalangeal joints. B, Rheumatoid arthritis. Note the marked ulnar deviation of the fingers. C, Gouty arthritis. Note the tophi filled with sodium urate crystals. (From Swartz MH: Textbook of physical diagnosis, ed 4, Philadelphia, 2002, Saunders.)

Classification of Synovial Joints

General overview of the body's musculature.

General overview of the body's musculature. A, Anterior view. B, Posterior view.

Muscles of the thorax.

Muscles of the thorax. Anterior view. Note the relationship of the internal and external intercostal muscles and placement of the diaphragm.

Muscles acting on the shoulder girdle.

Muscles acting on the shoulder girdle. A, Posterior view. The trapezius has been removed on the right to reveal the deeper muscles. B, Anterior view. The pectoralis major has been removed on both sides. The pectoralis minor has also been removed on the right side.

Muscles of the forearm.

Muscles of the forearm. A, Anterior view showing the right forearm (superficial). The brachioradialis muscle has been removed. B, Anterior view showing the right forearm (deeper than A). The pronator teres, flexor carpi radialis and ulnaris, and palmaris longus muscles have been removed. C, Anterior view showing the right forearm (deeper than A or B). The brachioradialis, pronator teres, flexor carpi radialis and ulnaris, palmaris longus, and flexor digitorum superficialis muscles have been removed. D, Posterior view showing the deep muscles of the right forearm. The extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris muscles have been cut to reveal deeper muscles.

Muscles that adduct the thigh. O, Origin; I, insertion.

Sports and Fitness. The rotator cuff stabilizes the shoulder during athletic activities.

Skeletal muscle striations.

Skeletal muscle striations. Color-enhanced scanning electron micrographs (SEMs) showing longitudinal views of skeletal muscle fibers. B shows detail of A at greater magnification. Note that the myofilaments of each myofibril form a pattern that when viewed together, produces the striated (striped) pattern typical of skeletal muscle. (A: Courtesy Dr. J.H. Venable, Department of Anatomy, Colorado State University, Fort Collins, CO. B: Courtesy Dr. H.E. Huxley.)

Role of calcium in muscle contraction.

Role of calcium in muscle contraction. Color-enhanced scanning electron micrograph (SEM) of a thin filament. When calcium is absent, the active myosin binding sites on actin are covered by tropomyosin. However, after calcium becomes available and binds to troponin, the tropomyosin is pulled out of its blocking position and reveals the active binding sites on actin. (From Lodish H: Molecular cell biology, ed 4, New York, 2000, WH Freeman.)

Aerobic and anaerobic respiration during muscular activity.

Aerobic and anaerobic respiration during muscular activity. A, Aerobic respiration (purple bars) can supply energy for muscle contraction for a longer time than can anaerobic respiration (purple). B, The lines show that 100% of the energy used at the beginning of maximal exercise comes from anaerobic processes. However, the muscles soon switch to aerobic sources of energy so after 1 hour of maximal exercise, nearly 100% of the energy comes from aerobic respiration in the muscle fibers. More information on aerobic and anaerobic respiration is found in Chapter 27.

Role of calcium in twitch and tetanus.

Role of calcium in twitch and tetanus. A, A single, sudden increase in calcium (Ca++) availability triggers the twitch contraction. B, Repeated stimuli maintain a high level of calcium, permitting sustained (tetanic) contraction. (Adapted from Pollard T, Earnshaw W: Cell biology, ed 2, Philadelphia, 2008, Saunders.)

Cardiac muscle fiber.

Cardiac muscle fiber. Unlike other types of muscle fibers, cardiac muscle fiber is typically branched and forms junctions, called intercalated disks, with adjacent cardiac muscle fibers. Like skeletal muscle fibers, cardiac muscle fibers contain sarcoplasmic reticula and T tubules—although these structures are not as highly organized as in skeletal muscle fibers.

Sports and Fitness. A, Types of muscle fibers.

Sports and Fitness. A, Types of muscle fibers. Using a special staining technique, this micrograph of a cross section of skeletal muscle tissue shows a mix of fiber types: R, red (slow) fibers; W, white (fast) fibers; and I, intermediate fibers.

The Epidermis

Epidermal cell types. Keratinocytes, most of the cells seen here, begin their life in the deepest layer of the epidermis and are pushed upward as more keratinocytes are formed. Melanocytes produce pigments. Epidermal dendritic cells (DCs) function in immunity. Tactile epithelial cells (Merkel cells) attach to sensory nerve endings to form "light touch" receptors.

Tanning

Tanning effects in skin. Photos showing skin effects of ultraviolet (UV) radiation on day 8 after exposure to increasing doses (1 through 7) in three skin types. Notice that the Caucasian skin involves more redness (from burning) than the darker skin types, which become even darker in response to higher doses of UV radiation. (From Rouzaud F, Kadekaro A, Abdel-Malek ZA, Hearing VJ: MC1R and the response of melanocytes to ultraviolet radiation,

Role of skin in homeostasis of body temperature.

Role of skin in homeostasis of body temperature. Body temperature is continually monitored by nerve receptors in the skin and other parts of the body. These receptors feed information back to the hypothalamus of the brain, which compares the actual temperature with the set point temperature and then sends out an appropriate correction signal to effectors. If actual body temperature is above the set point temperature, sweat glands in the skin are signaled to increase their secretion and thus promote evaporation and cooling. At the same time, blood vessels in the dermis are signaled to dilate and thus promote radiation of heat away from the skin’s surface.

Onycholysis.

Onycholysis. Note that separation of this nail from the nail bed begins at the free edge. Minor trauma to long fingernails is the most common cause. (From Habif TP: Clinical dermatology, ed 2, St Louis, 1990, Mosby.)

Skin cancers.

Skin cancers. (A: From Goldman L, Ausiello D, Cecil textbook of medicine, ed 23, Philadelphia, 2003, Saunders. B: From Noble J: Textbook of primary care medicine, ed 3, Philadelphia, 2001, Mosby. C: From Townsend C, Beauchamp RD, Evers BM, Mattox K: Sabiston textbook of surgery, ed 18, Philadelphia, 2008, Saunders. D: From Rakel R: Textbook of family medicine, ed 7, Philadelphia, 2007, Saunders.)

Subcutaneous and intradermal injections.

The Long Bone

Long bone. A, Partial frontal section of a long bone (tibia) showing cancellous and compact bone. B, Frontal section of a long bone. (B: From White T, Human osteology, ed 2, Philadelphia, 2000, Academic Press.)

Osteocyte

Osteocyte. A, Sketch showing osteocytes trapped inside hollow lacunae within hard bone matrix. B, Scanning electron micrograph showing an osteocyte within a lacuna. Note the cytoplasmic process (arrow) extending into a canaliculus below. The cell is surrounded by collagen fibers and mineralized bone. (A: From Muscolino J: Kinesiology, St Louis, 2006, Mosby. B: From Erlandsen SL, Magney J: Color atlas of histology, St Louis, 1992, Mosby.)

Epiphyseal plate structure.

Epiphyseal plate structure. An epiphyseal plate between the epiphyses and diaphyses of a long bone. Photograph shows the zones of the epiphyseal plate. (Ed Reschke.)

Types of cartilage.

Types of cartilage. A, Hyaline cartilage of the trachea. B, Elastic cartilage of the epiglottis. Note the black elastic fibers in the cartilage matrix and the perichondrium layers on both surfaces. C, Fibrocartilage of an intervertebral disk. (A-B: Dennis Strete.)

Skull viewed from the right side.

Bones of the skull.

Bones of the skull. C, Frontal bone viewed from the front and slightly above. D, Occipital bone viewed from below.

Bones of the skull.

Bones of the skull. K, Right lacrimal bone viewed from the lateral side. L, Right nasal bone viewed from the lateral side.

The vertebral column.

The vertebral column. A, Right lateral view. B, Anterior view. C, Posterior view. The photo inset shows a midline sagittal magnetic resonance image (MRI) of the vertebral column. (From Williams P: Gray's anatomy, ed 38, Philadelphia, Churchill Livingstone, 1996.)

Articulation of a rib and vertebra.

Articulation of a rib and vertebra. A, Note the head of the rib articulating with the vertebral body and the tubercle of the rib articulating with the transverse process of the vertebra. B, Anatomical components of a typical rib (fifth rib) viewed from behind. (B: From Abrahams P, Marks S, Hutchings R: McMinn's color atlas of human anatomy, ed 5, Philadelphia, 2003, Mosby.)

Left coxal (hip) bone.

Left coxal (hip) bone. The left coxal bone is disarticulated from the bony pelvis and viewed from the side. (From Abrahams P, Marks S, Hutchings R: McMinn's color atlas of human anatomy, ed 5, Philadelphia, 2003, Mosby.)

Mastoiditis.

Mastoiditis. Note redness and swelling over the mastoid process of the temporal bone. (Courtesy Dr. N. Blevins, New England Medical Center, Boston.)

Types of synovial joints.

Types of synovial joints. Uniaxial: A, hinge, and B, pivot. Biaxial: C, saddle, and D, condyloid. Multiaxial: E, ball and socket, and F, gliding.

The right knee joint.

The right knee joint. A and B, Labeled dissection of the right knee viewed from in front. C and D, Viewed from behind. (B-D: Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

Range of motion.

Movements and ROM. A, Flexion and extension. Extension beyond the anatomical position is sometimes called hyperextension. B, Lateral bending. C, Rotation (supine position). D, Rotation (standing position). (A-C: From Barkauskas V, Baumann L, Stoltenberg-Allen K, Darling-Fisher C: Health and physical assessment, ed 2, St Louis, 1998, Mosby.)

Movements of the fingers and thumb.

Movements of the fingers and thumb. A, Flexion of the metacarpophalangeal joints and flexion of the interphalangeal joints. B, Extension of the metacarpophalangeal joints and flexion of the interphalangeal joints. C, Extension of the metacarpophalangeal and interphalangeal joints. D, Opposition of the thumb. E, Flexion of the thumb. (From Abrahams P, Marks S, Hutchings R: McMinn's color atlas of human anatomy, ed 5, Philadelphia, 2003, Mosby.)

Arthroscopy.

Arthroscopy. A, Fiberoptic light source inserted into a joint. B, Internal view of the joint. (Courtesy Lanny L. Johnson, MD, East Lansing, MI.)

Structure of a muscle organ.

Structure of a muscle organ. A, Note that the connective tissue coverings, the epimysium, perimysium, and endomysium, are continuous with each other and with the tendon. Note also that muscle fibers are held together by the perimysium in groups called fascicles. B, Diagram showing the arm in cross section. Note the relationships of superficial and deep fascia to individual muscles and other structures in the plane of section.

General overview of the body's musculature. C, Lateral view.

Muscles of the trunk and abdominal wall.

Muscles of the trunk and abdominal wall. A, Superficial muscles are visible on the right side of the body and deeper muscles on the left side of the body. B, Transverse section of the anterior wall above the umbilicus (see inset for location).

Muscles that move the upper part of the arm. A, Anterior view. B, Posterior

Muscles of the anterior aspect of the right forearm.

Gluteal muscles. A, Gluteus maximus. B, Gluteus minimus. C, Gluteus medius. O, Origin; I, insertion.

The carpal tunnel.

Health Matters. The carpal tunnel. The median nerve and muscles that flex the fingers pass through a concavity in the wrist called the carpal tunnel.

Structure of myofilaments.

Structure of myofilaments. A, Thin myofilament. B, Thick myofilament. C, Cross section of several thick and thin myofilaments showing the relative positions of myofilaments and the myosin heads that will form cross bridges between them.

Cross bridges.

Cross bridges. Color-enhanced scanning electron micrograph (SEM) showing the myosin heads functioning as cross bridges that connect the thick filaments to the thin filaments, pulling on the thin filaments and causing them to slide. (From Lodish H: Molecular cell biology, ed 4, New York, 2000, WH Freeman.)

The role of skeletal muscle tissues in maintaining a constant body temperature.

The role of skeletal muscle tissues in maintaining a constant body temperature. This diagram shows that a drop in body temperature caused by cold weather can be corrected by a negative feedback mechanism that triggers shivering (muscle contraction), which in turn produces enough heat to warm the body.

Strength

The strength of muscle contraction compared with the strength of the stimulus. After the threshold stimulus is reached, a continued increase in stimulus strength produces a proportional increase in muscle strength until the maximal level of contraction strength is reached.

Cardiac and skeletal muscle contractions compared.

Cardiac and skeletal muscle contractions compared. A brief nerve impulse triggers a brief twitch contraction in skeletal muscle (blue), but a prolonged impulse in the heart tissue produces a rather slow, drawn out contraction in cardiac muscle (red).

Three styles of twitch contraction

Sports and Fitness. B, Three styles of twitch contraction. Different muscle organs have different proportions of slow, fast, and intermediate fibers and thus produce different styles of twitch contractions in a myogram.

Arrector Pili

Arrector pili muscle. When the arrector pili muscle contracts, it pulls the follicle and hair into a more perpendicular position, thus "fluffing up" the hair. Notice how a "goose bump" is raised around the hair shaft.

Age Spots

Age spots. Hyperpigmentations from the cumulative effects of UV exposure over the years are often called "age spots" or "liver spots." (From Regezi JA, Sciubba JJ, Jordan RCK: Oral pathology: clinical pathologic correlations, ed 5, St Louis, 2008, Saunders.)

Hair Follicle

Hair follicle. A, Relationship of a hair follicle and related structures to the epidermal and dermal layers of the skin. B, Enlargement of a hair follicle wall and hair bulb. C, Scanning electron micrograph showing shafts of hair extending from their follicles. (C: Copyright © by David Scharf, 1986, 1993.)

Skin glands.

Skin glands. Several types of exocrine glands occur in the skin.

Body temperature.

Body temperature. This diagram, modeled after a thermometer, shows some physiological consequences of abnormal body temperature. The inset shows a range of body temperatures at which normal function is possible. Ideally, body temperature should be near 37° C (98.6° F), but the body can operate normally within the range shown if conditions are not ideal. (Barbara Cousins.)

Jaundice

Jaundice. Yellowish discoloration of the skin and other tissues by bile pigments was, in the case seen here, caused by a liver infection. The patient was infected with hepatitis B by a contaminated tattoo needle. The yellow tinge of the skin can be best seen by comparing the patient's skin color with that of the physician's hand.

The Flat Bone

Flat bone. A, Horizontal section of a flat bone of the skull (frontal bone) showing cancellous and compact bone. B, Photograph of a frontal bone cut in horizontal section. (B: From Moses K, Nava P, Banks J, Petersen D: Moses atlas of clinical gross anatomy, Philadelphia, 2005, Mosby.)

Calcium Regulation

Calcium homeostasis. Calcitonin and parathyroid hormones have antagonistic (opposing) effects that help to maintain a homeostatic balance of calcium in the blood.

Growth of epiphyseal plate.

Growth of epiphyseal plate. Diagrams showing steps in ossification on either side of the epiphyseal plate.

Osteoporosis.

Osteoporosis. A, Compare the normal vertebral body (left) with the osteoporotic specimen (right). Note that the osteoporotic vertebral body has been shortened by compression fractures. B, Scanning electron micrograph (SEM) of normal bone. C, SEM of osteoporotic bone. Note the loss of trabeculae and appearance of enlarged pores caused by osteoporosis. (From Kumar V, Abbas A, Fausto N: Robbins and Cotran pathologic basis of disease, ed 7, Philadelphia, 2005, Saunders.)

Floor of the cranial cavity viewed from above.

Bones of the skull.

Bones of the skull. E, Sphenoid bone. E1, Superior view; E2, posterior view.

Bones of the skull.

Bones of the skull. M, Right half of the mandible. M1, Medial view; M2, lateral view.

Vertebrae.

Vertebrae. A, Lateral and superior views of C1, the atlas. B, Lateral and superior views of C2, the axis. C, Base of the skull showing C1 (atlas) and C2 (axis) in posterior view. (From Gosling J, Harris P, Whitmore I, Willan P: Human anatomy, ed 4, Philadelphia, 2002, Mosby.)

Right scapula.

Right scapula. A, Anterior view. B, Posterior view. C, Lateral view. D, Posterior view showing articulation of the right scapula with the clavicle. (The inset shows the relative position of the right scapula within the entire skeleton.) (D: Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

Bones of the thigh and leg.

Bones of the thigh and leg. A, Right femur, anterior surface. B, Right femur, posterior view. C, Right tibia and fibula, anterior surface. D, Anterior aspect of the right knee skeleton. E, Right tibia and fibula, posterior aspect. (The inset shows the relative position of the bones of the thigh and leg within the entire skeleton.) (D-E: Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

Abnormal spine curvatures.

Abnormal spine curvatures. A, Lordosis. B, Kyphosis. C, Scoliosis. Black arrows highlight areas of abnormal curvature.

The shoulder joint.

The shoulder joint. A, Artist's diagram, and B, dissection photo (anterior views). C, Artist's diagram, and D, dissection photo (viewed from behind through shoulder joint). (B-D: Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

Knee Joint.

Knee joint (sagittal section). Cadaver dissection showing the articular surfaces and related structures. (From Gosling J, Harris P, Whitmore I, Willan P: Human anatomy, ed 4, Philadelphia, 2002, Mosby.)

Movements of the jaw.

Movements of the jaw. A, Retraction and protraction. B, Elevation and depression.

Movements and ROM of the hip.

Movements and ROM of the hip. A, Hip flexion, knee extended. B, Hip flexion, knee flexed. C, Internal rotation. D, Abduction and adduction. (From Seidel HM, Ball JW, Dains JE, Benedict GW: Mosby's guide to physical examination, ed 5, St Louis, 2003, Mosby.)

Sports and Fitness. Knee injury.

Muscle shape and fiber arrangement.

Muscles of facial expression and mastication. Lateral view.

Dissection photo of the abdominal wall.

Dissection photo of the abdominal wall. The covering rectus sheaths, the left oblique muscles, and part of the left rectus have been removed. (From Gosling J, Harris P, Whitmore I, Willan P: Human anatomy, ed 4, Philadelphia, 2002, Mosby.)

Rotator cuff muscles.

Rotator cuff muscles. Note the tendons of the teres minor, infraspinatus, supraspinatus, and subscapularis muscles surrounding the head of the humerus.

Intrinsic muscles of the hand—anterior (palmar) view.

Quadriceps

Quadriceps femoris group of thigh muscles. A, Vastus medialis. B, Rectus femoris. C, Vastus intermedius. D, Vastus lateralis. O, Origin; I, insertion.

Health Matters. Intramuscular injections.

Cross section of myofibrils.

Cross section of myofibrils. Color-enhanced scanning electron micrographs (SEMs) showing a cross section from a skeletal muscle fiber. Note the dense arrangement of thick and thin filaments, seen here in cross section as mere dots. Note also the dark glycogen granules and sarcoplasmic reticulum tubules sandwiched between the myofibrils. (From Leeson CR, Leeson T, Paparo A: Text/atlas of histology, St Louis, 1988, Saunders.)

Sliding-filament model.

Sliding-filament model. A, During contraction, myosin cross bridges pull the thin filaments toward the center of each sarcomere, thus shortening the myofibril and the entire muscle fiber. B, Color-enhanced transmission electron micrographs (TEMs) showing the shortening of a sarcomere caused by the sliding of filaments during muscle contraction. (B: Courtesy H.E. Huxley, Brandeis University, Waltham, MA.)

Motor unit.

Motor unit. A motor unit consists of one somatic motor neuron and the muscle fibers supplied by its branches. A, Photomicrograph showing a nerve (black) branching to supply several dozen individual muscle fibers (red). B, Sketch showing a single motor unit. C, Diagram showing several motor units within the same muscle organ. (B: Courtesy Dr. Paul C. Letourneau, Department of Anatomy, Medical School, University of Minnesota, MN.)

The length- tension relationship.

The length- tension relationship. As this graph of muscle tension shows, the maximum strength that a muscle can develop is directly related to the initial length of its fibers. At a short initial length, the sarcomeres are already compressed, and thus the muscle cannot develop much tension (position A). Conversely, the thick and thin myofilaments are too far apart in an overstretched muscle to generate much tension (position C). Maximum tension can be generated only when the muscle has been stretched to a moderate, optimal length (position B).

Smooth muscle fiber.

Smooth muscle fiber. A, Thin bundles of myofilaments span the diameter of a relaxed fiber. The scanning electron micrograph (above) shows that the surface of the cell is rather flat when the fiber is relaxed. B, During contraction, sliding of the myofilaments causes the fiber to shorten by "balling up." The micrograph (above) shows that the fiber becomes shorter and thicker and exhibits "dimples" where the myofilament bundles are pulling on the plasma membrane. (Courtesy Dr. Frederic S. Fay, Department of Physiology, University of Massachusetts, Worcester, MA.)

Sports and Fitness. C, Proportions of fiber types in muscle tissue.

Sports and Fitness. C, Proportions of fiber types in muscle tissue. A person with a spinal cord injury eventually loses nearly all of the postural slow fibers while retaining mostly intermediate and fast fibers. In an extreme endurance athlete, on the other hand, the slow fibers develop so much that they greatly dominate the faster fiber types.

Touch

Skin receptors. Receptors are sensitive nerve endings that make it possible for the skin to act as a sense organ. A, This tactile (Meissner) corpuscle is capable of detecting light touch (slight pressure). B, Another skin receptor is the lamellar corpuscle, also called a Pacini corpuscle, which detects sensations of deep pressure. (Barbara Cousins.)

Cyanosis

The blue discoloration of the fingers of this light-skinned individual is caused by the diffusion of light reflected off dark, unoxygenated hemoglobin in the blood vessels of the skin. The fingertips have an especially high volume of blood and thus look bluer than other regions of the skin. (From Epstein O, Perkin GD, Cookson J, de Bono D: Clinical examination, ed 3, St Louis, 2003, Mosby.)

Gray Hair

Gray hair. Gray hair results from a scattered arrangement of both white (pigmentless) hairs and darker (pigmented) hairs. (Copyright Kevin Patton, Lion Den Inc, Weldon Spring, MO.)

Aged skin.

Aged skin. In late adulthood, wrinkles in the skin often develop—especially in areas of frequent movement such as on the hands, around the mouth, and around the eyelids. (From Habif TP: Clinical dermatology, ed 4, St Louis, Mosby, 2004.)

"Rule of nines."

"Rule of nines." The "rule of nines" is one method used to estimate amount of skin surface burned in an adult.

Acne

Compact and Cancellous Bone

Compact and cancellous bone in a long bone. A, Longitudinal section of a long bone showing both cancellous and compact bone. B, Magnified view of compact bone.

Bone development.

Bone development. Diagram showing osseous development at birth.

Epiphyseal fracture.

Epiphyseal fracture. Radiograph showing an epiphyseal fracture of the distal end of the femur in a young athlete. Note the separation of the diaphysis and epiphysis at the level of the growth plate. (From Booher JM, Thibodeau GA: Athletic injury assessment, St Louis, 1985, Mosby.)

Rickets.

Rickets. Bowing of legs in this toddler is due to poorly mineralized bones from rickets. (From Kumar V, Abbas A, Fausto N: Robbins and Cotran pathologic basis of disease, ed 7, Philadelphia, 2005, Saunders.)

Skull viewed from below.

Bones of the skull.

Bones of the skull. F, Ethmoid bone. F1, Superior view; F2, lateral view; F3, anterior view.

The paranasal sinuses. A, Lateral view. B, Frontal view.

The paranasal sinuses. A, Lateral view. B, Frontal view.

Vertebrae.

Vertebrae. D, Lateral and superior views of a cervical vertebra, C7 (note the prominent spinous process). (From Gosling J, Harris P, Whitmore I, Willan P: Human anatomy, ed 4, Philadelphia, 2002, Mosby.)

Bones of the arm (right arm, anterior view).

Bones of the arm (right arm, anterior view). A, Humerus (upper part of the arm). B, Radius and ulna (forearm). C, Elbow joint, showing how the distal end of the humerus joins the proximal ends of the radius and ulna. (The inset shows the relative position of the right arm bones within the entire skeleton.) (C: Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

The foot.

The foot. A, Bones of the right foot viewed from above. The tarsal bones consist of the cuneiforms, navicular, talus, cuboid, and calcaneus. B, Posterior aspect of the right ankle skeleton and inferior aspect of the right foot skeleton. C, X-ray film of the left foot showing prominent sesamoid bones (arrows) near the distal end (head) of the first metatarsal bone of the great toe. (B: Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

Palpable bony landmarks.

The elbow joint.

The elbow joint. A, Sagittal section through the elbow joint. B, Dissection photo showing the anterior view of the proximal end of the ulna with attached annular ligament. (From Gosling J, Harris P, Whitmore I, Willan P: Human anatomy, ed 4, Philadelphia, 2002, Mosby.)

Ankle joint.

Ankle joint. A, Dorsum of the ankle and foot showing surface relationships to underlying bones. B, Dissection photo of the ankle joint. (A: From Lumley J: Surface anatomy, ed 3, Edinburgh, 2002, Churchill Livingstone. B: Courtesy Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.)

Range of motion in the spine

Movements and ROM of the thoracic and lumbar spine. A, Flexion. B, Hyperextension. C, Lateral bending. D, Rotation of the upper part of the trunk. (From Seidel HM, Ball JW, Dains JE, Benedict GW: Mosby's guide to physical examination, ed 5, St Louis, 2003, Mosby.)

Movements and ROM of the knee.

Movements and ROM of the knee. Flexion may reach 130 degrees. Extension occurs with movement from a 130-degree flexed position back to the 0-degree position. Hyperextension of 0 degrees to 15 degrees is possible in many individuals. (From Barkauskas V, Baumann L, Stoltenberg-Allen K, Darling-Fisher C: Health and physical assessment, ed 2, St Louis, 1998, Mosby.)

Sports and Fitness. Torn ligaments.

Attachments of a skeletal muscle.

Attachments of a skeletal muscle. A, Origin and insertion of a skeletal muscle. A muscle originates at a relatively stable part of the skeleton (origin) and inserts at the skeletal part that is moved when the muscle contracts (insertion). B, Movement of the forearm during weightlifting. Muscle contraction moves bones, which serve as levers, and by acting on joints, which serve as fulcrums for those levers. See the text for discussion and review Figure 10-4, which illustrates types of levers.

Muscles of facial expression and mastication. Anterior view.

Muscles of the back.

Muscles of the back. A, Superficial (left) and intermediate (right) muscle dissection of the back—posterior view. The illustration shows a two-stage dissection. Superficial muscles of the neck and back are shown on the left side and an intermediate-depth dissection is shown on the right.

Cross sections (proximal to distal) through the upper extremity.

Cross sections (proximal to distal) through the upper extremity. A, Section at the junction of the proximal and middle thirds of the humerus. B, Section just proximal to the medial epicondyle of the humerus. C, Section at the level of the radial tuberosity. D, Section at the middle of the forearm. In each section you are viewing the superior (proximal) aspect of the specimen.

Iliopsoas muscle (iliacus, psoas major, and psoas minor muscles). O, Origin; I, insertion.

Hamstrings

Hamstring group of thigh muscles. A, Biceps femoris. B, Semitendinosus. C, Semimembranosus. O, Origin; I, insertion.

Structure of skeletal muscle.

Structure of skeletal muscle. A, Skeletal muscle organ composed of bundles of contractile muscle fibers held together by connective tissue. B, Greater magnification of a single fiber showing smaller fibers—myofibrils—in the sarcoplasm. Note the sarcoplasmic reticulum and T tubules forming a three-part structure called a triad. C, Myofibril magnified further to show a sarcomere between successive Z disks (Z lines). Cross striae are visible. D, Molecular structure of a myofibril showing thick myofilaments and thin myofilaments.

Neuromuscular junction (NMJ).

Neuromuscular junction (NMJ). A, Micrograph showing four neuromuscular junctions (NMJs). Three are surface views (arrows) and one is a side view (arrowhead). N, Nerve fibers; M, muscle fibers. B, This sketch shows a side view of the NMJ. Note how the distal end of a motor neuron fiber forms a synapse, or "chemical junction," with an adjacent muscle fiber. Neurotransmitter molecules (specifically, acetylcholine, or Ach) are released from the neuron's synaptic vesicles and diffuse across the synaptic cleft. There they stimulate receptors in the motor endplate region of the sarcolemma. (A: From Leeson CR, Leeson T, Paparo A: Text/atlas of histology, St Louis, 1988, Saunders.)

Simplified contracting sarcomere.

Simplified contracting sarcomere. This diagram illustrates the concept of muscle contraction as a sort of tug-of-war game in which the myosin heads (shown here as little people) hold onto thin filament "ropes"—thus forming cross bridges. As the myosin heads pull on the thin filaments, the Z disks (Z lines) get closer together—thus shortening the sarcomere. Likewise, the short length of a sarcomere may be held in position by the continued effort of the myosin heads.

Myography.

Myography. This classic type of myograph, called a kymograph, records muscle contractions as graphs showing changes in length. An isolated muscle moves the pen upward during contraction, and the weight pulls the muscle and pen downward as the muscle relaxes. A change in tension produces this change in length. Electrical voltage simulates a nerve impulse to stimulate the fibers in the muscle. Modern myography often uses computer-based systems that record similar muscle tension graphs.

The stretch reflex.

The stretch reflex. The strength of a muscle organ can be matched to the load imposed on it by a negative feedback response centered in the spinal cord. Increased stretch (caused by increased load) is detected by a sensory nerve fiber attached to a muscle cell (called a muscle spindle). The information is integrated in the spinal cord and a correction signal is relayed through motor neurons back to the same muscle, which increases tension to return to the set point muscle length.

Types of smooth muscle.

Types of smooth muscle. A, Single-unit (visceral) smooth muscle. Neurotransmitters released from varicosities (bulges) in the nerve fiber trigger impulses in the smooth muscle membranes—an event that is transmitted to adjacent muscle fibers through gap junctions. Thus a large mass of muscle fibers acts as a single unit. B, Multiunit smooth muscle. Each muscle fiber is triggered independently by nerve stimulation.

Effects of Exercise on Skeletal Muscles.

Effects of Exercise on Skeletal Muscles. A, Disuse atrophy. The arrow points to a group of muscle fibers that have atrophied from disuse (in this case from nerve damage). Notice how much smaller they are than the surrounding, normal fibers.