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chap08outline - Chapter 8 Muscular System 8.1...

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Chapter 8 - Muscular System 8.1 Introduction (p. 178 ) A. The three types of muscle in the body are skeletal, smooth, and cardiac muscle. B. This chapter focuses on skeletal muscle. 8.2 Structure of a Skeletal Muscle (p. 178) A. Each muscle is an organ, comprised of skeletal muscle tissue, connective tissues, nervous tissue, and blood. B. Connective Tissue Coverings (p. 178; Fig. 8.1) 1. Layers of dense connective tissue, called fascia, surround and separate each muscle. 2. This connective tissue extends beyond the ends of the muscle and gives rise to tendons that are fused to the periosteum of bones. 3. Sometimes tendons are broad sheets of connective tissue called aponeuroses. 4. The layer of connective tissue around each whole muscle is the epimysium; the perimysium surrounds individual bundles (fascicles) within each muscle; and each muscle cell (fiber) is covered by a connective tissue layer called endomysium. C. Skeletal Muscle Fibers (p. 179; Figs. 8.2-8.4) 1. Each muscle fiber is a single, long, cylindrical muscle cell. 2. Beneath the sarcolemma (cell membrane) lies sarcoplasm (cytoplasm) with many mitochondria and nuclei; the sarcoplasm contains myofibrils. a. Thick filaments of myofibrils are made up of the protein myosin. b. Thin filaments of myofibrils are made up of the protein actin. c. The organization of these filaments produces striations. 3. A sarcomere extends from Z line to Z line. a. I bands (light bands) made up of actin filaments are anchored to Z lines. b. A bands (dark bands) are made up of overlapping thick and thin filaments. c. In the center of A bands is an H zone, consisting of myosin filaments only. 4. Beneath the sarcolemma of a muscle fiber lies the sarcoplasmic reticulum (endoplasmic reticulum), which is associated with transverse (T) tubules (invaginations of the sarcolemma). a. Each T tubule lies between two cisternae of the sarcoplasmic reticulum. b. The sarcoplasmic reticulum and transverse tubules activate the muscle contraction mechanism when the fiber is stimulated. D. Neuromuscular Junction (p. 181; Fig. 8.5) 1. The site where the motor neuron and muscle fiber meet is the neuromuscular junction. a. The muscle fiber membrane forms a motor end plate in which the sarcolemma is tightly folded and where nuclei and mitochondria are abundant. b. The cytoplasm of the motor neuron contains numerous mitochondria and synaptic vesicles storing neurotransmitters. E. Motor Units (p. 181; Fig. 8.6) 1. A motor neuron and the muscle fibers it controls make up a motor unit; when stimulated to do so, the muscle fibers of the motor unit contract all at once. 8.3 Skeletal Muscle Contraction (p. 182; Table 8.1) A. Muscle contraction involves several components that result in the shortening of sarcomeres,
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and the pulling of the muscle against its attachments. B. Role of Myosin and Actin (p. 182; Figs. 8.7-8.9) 1. Myosin consists of two twisted strands with globular cross-bridges projected outward along the strands.
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