Saladin: Anatomy & 10. The Muscular System Text © The McGraw−Hill Physiology: The Unity of Companies, 2003 Form and Function, Third Edition CHAPTER 10 The Muscular System Muscles of the thigh to upper calf (MRI) CHAPTER OUTLINE The Structural and Functional Organization of Muscles Acting on the Shoulder and Upper Muscles 326 Limb 352 INSIGHTS • The Functions of Muscles 326 • Muscles Acting on the Scapula 352 • Connective Tissues of a Muscle 326 • Muscles Acting on the Humerus 356 10.1 Medical History: Discovery of a • General Anatomy of Skeletal Muscles 328 • Muscles Acting on the Forearm 357 New Muscle 342 • Coordinated Action of Muscle Groups 328 • Muscles Acting on the Wrist and Hand 361 10.2 Clinical Application: Heavy Lifting • Intrinsic and Extrinsic Muscles 329 and Back Injuries 349 • Muscle Innervation 329 Muscles Acting on the Hip and Lower 10.3 Clinical Application: Hernias 351 • How Muscles Are Named 330 Limb 369 10.4 Clinical Application: Carpal • A Learning Strategy 330 • Muscles Acting on the Hip and Femur 369 Tunnel Syndrome 365 • Muscles Acting on the Knee 373 10.5 Clinical Application: Muscles of the Head and Neck 330 • Muscles Acting on the Foot 374 Intramuscular Injections 366 • Muscles of Facial Expression 330 10.6 Clinical Application: Athletic Connective Issues 387 • Muscles of Chewing and Swallowing 335 Injuries 386 • Muscles Acting on the Head 343 Chapter Review 388 Muscles of the Trunk 345 • Muscles of Respiration 345 • Muscles of the Abdomen 346 • Muscles of the Back 347 • Muscles of the Pelvic Floor 350 Brushing Up To understand this chapter, it is important that you understand or brush up on the following concepts: • Gross anatomy of the skeleton (chapter 8) • Movements of synovial joints (pp. 302–307) 325 Saladin: Anatomy & 10. The Muscular System Text © The McGraw−Hill Physiology: The Unity of Companies, 2003 Form and Function, Third Edition 326 Part Two Support and Movement he muscular system consists of about 600 skeletal muscles— parts. Muscular contractions also move body contents Tstriated muscles that are usually attached to bone. (The term in the course of respiration, circulation, digestion, does not include smooth or cardiac muscle.) The form and function defecation, urination, and childbirth. of the muscular system occupy a place of central importance in • Stability. Muscles maintain posture by resisting the several fields of health care and fitness. Physical and occupational pull of gravity and preventing unwanted movements. therapists must be well acquainted with the muscular system to They hold some articulating bones in place by design and carry out rehabilitation programs. Nurses and other maintaining tension on the tendons. health-care providers often move patients who are physically inca- pacitated, and to do this safely and effectively requires an under- • Communication. Muscles are used for facial standing of joints and muscles. Even to give intramuscular injec- expression, other body language, writing, and speech. tions safely requires a knowledge of the muscles and the nerves and • Control of body openings and passages. Ringlike blood vessels associated with them. Coaching, movement science, sphincter muscles around the eyelids, pupils, and sports medicine, and dance benefit from a knowledge of skeleto- mouth control the admission of light, food, and drink muscular anatomy and mechanics. 1 into the body; others that encircle the urethral and Myology, the study of muscles, is closely related to what we anal orifices control elimination of waste; and other have covered in the preceding chapters. It relates muscle attach- sphincters control the movement of food, bile, and ments to the bone structures described in chapter 8 and muscle other materials through the body. function to the joint movements described in chapter 9. In this chap- ter, we consider the gross anatomy of the muscular system and how • Heat production. The skeletal muscles produce as it relates to joint movements. In chapter 11, we examine the mecha- much as 85% of our body heat, which is vital to the Chapter 10 Chapter nisms of muscle contraction at the cellular and molecular levels. functioning of enzymes and therefore to all of our metabolism. Some of these functions are shared by skeletal, cardiac, and smooth muscle. The remainder of this chapter, how- The Structural and Functional ever, is concerned only with skeletal muscles. Organization of Muscles Connective Tissues of a Muscle Objectives When you have completed this section, you should be able to A skeletal muscle is composed of both muscular tissue and • list several functions of muscles; connective tissue (fig. 10.1). A skeletal muscle cell (muscle ␮ • describe the connective tissues associated with a skeletal fiber) is about 10 to 100 m in diameter and up to 30 cm muscle; long. It is surrounded by a sparse layer of areolar connective 2 • explain what is meant by the origin, insertion, belly, action, tissue called the endomysium (EN-doe-MIZ-ee-um), and innervation of a muscle; which allows room for blood capillaries and nerve fibers to • describe the various shapes of skeletal muscles and relate this reach each muscle fiber. Muscle fibers are grouped in bun- 3 to their functions; dles called fascicles (FASS-ih-culs), which are visible to • describe the ways that muscles work in groups to aid, oppose, the naked eye as parallel strands. These are the “grain” in a or moderate each other’s actions; cut of meat; tender meat is easily pulled apart along its fas- • distinguish between intrinsic and extrinsic muscles; and cicles. Each fascicle is separated from neighboring ones by 4 • translate several Latin words commonly used in the naming a connective tissue sheath called the perimysium, usually of muscles. somewhat thicker than the endomysium. The muscle as a whole is surrounded by still another connective tissue layer, the epimysium.5 The epimysium grades impercepti- The Functions of Muscles bly into connective tissue sheets called fasciae (FASH-ee- ee)—deep fasciae between adjacent muscles and a superfi- A muscle is an organ specialized to produce movement of cial fascia (hypodermis) between the muscles and skin. The a body part. Its cells convert the chemical energy of ATP superficial fascia is very adipose in areas such as the but- into the mechanical energy of motion and exert a useful tocks and abdomen, but the deep fasciae are devoid of fat. pull on another tissue. More specifically, muscle contrac- There are two ways a muscle can attach to a bone. In tion serves the following overlapping functions: a direct (fleshy) attachment, collagen fibers of the epimy- • Movement. Most obviously, the muscles enable us to move from place to place and to move individual body 2endo ϭ within ϩ mys ϭ muscle 3fasc ϭ bundle ϩ icle ϭ little 4peri ϭ around 1myo ϭ muscle ϩ logy ϭ study of 5epi ϭ upon, above Saladin: Anatomy & 10. The Muscular System Text © The McGraw−Hill Physiology: The Unity of Companies, 2003 Form and Function, Third Edition Chapter 10 The Muscular System 327 Articular cartilage Lateral Medial Skin Superficial fascia (adipose tissue) Nerve Vein Humerus Artery Deep fascia Skeletal muscle Individual muscle Fascicles Fascicle Muscle Tendon (b) fibers 10 Chapter Deep fascia Perimysium Endomysium Endomysium Osseous tissue Perimysium Epimysium Periosteum Muscle fiber, c.s. (cut) Fascicle, c.s. Fascicle, l.s. (a) (c) Figure 10.1 Connective Tissues of a Muscle. (a) The muscle-bone attachment. Here there is a continuity of connective tissues from the endomysium around the muscle fibers, to the perimysium, epimysium, deep fascia, and tendon, grading into the periosteum and finally the matrix of the bone. (b) A cross section of the arm showing the relationship of neighboring muscles to fascia and bone. (c) Muscle fascicles in the tongue. Vertical fascicles passing between the dorsal and ventral surfaces of the tongue are seen alternating with cross-sectioned horizontal fascicles that pass from the tip to the rear of the tongue. A fibrous perimysium can be seen between the fascicles, and endomysium between the muscle fibers within each fascicle. sium are continuous with the periosteum, the fibrous In some cases, the epimysium of one muscle attaches sheath around a bone. The red muscle tissue appears to to the fascia or tendon of another or to collagen fibers of emerge directly from the bone. The intercostal muscles the dermis. The ability of a muscle to produce facial between the ribs show this type of attachment. In an indi- expressions depends on the latter type of attachment. rect attachment, the collagen fibers of the epimysium con- Some muscles are connected to a broad sheetlike tendon tinue as a strong fibrous tendon that merges into the called an aponeurosis6 (AP-oh-new-RO-sis). This term periosteum of a nearby bone (fig. 10.1a). The attachment originally referred to the tendon located beneath the scalp, of the biceps brachii muscle to the scapula is one of many but now it also refers to similar tendons associated with examples. Some collagen fibers of the periosteum con- certain abdominal, lumbar, hand, and foot muscles (see tinue into the bone matrix as perforating fibers (see chap- figs. 10.15a and 10.16). ter 7), so there is a strong structural continuity from In some places, groups of tendons from separate endomysium to perimysium to epimysium to tendon to muscles pass under a band of connective tissue called a periosteum to bone matrix. Excessive stress is more likely to tear a tendon than to pull it loose from the muscle or bone. 6apo ϭ upon, above ϩ neuro ϭ nerve Saladin: Anatomy & 10. The Muscular System Text © The McGraw−Hill Physiology: The Unity of Companies, 2003 Form and Function, Third Edition 328 Part Two Support and Movement retinaculum.7 One of these covers each surface of the wrist 2.