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Chapter 9 Muscular System

Chapter 9 Muscular System - The Muscular System overview I...

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The Muscular System - overview I. Functions A. Move skeleton B. Maintain posture/position C. Protect internal organs (support soft tissues—six pack) D. Gate openings: mouth, anus, urinary tract (guards entrances and exits) E. Produce heat (maintain body temperature) II. Anatomy of Skeletal Muscles A. Muscles, Fascicles (bundle of muscle fibers), and Muscle Cells (Myocytes) B. Connective tissues: Epimysium : dense collagen fibers, separates muscle from surrounding tissues and organs; Perimysium : divides muscle into compartments each containing fascicles, blood vessels, nerves, consists of cartilage and elastic fibers; and Endomysium : surrounds individual skeletal muscle cells found in a complete network called fascicles, capillary networks, satellite cells (embryonic stem cells to repair damaged cells), and nerve fibers. All of these come together to form a tendon C. Blood vessels, Nerves: supply each individual cell III. Skeletal Muscle Cells: Cytology sacro=flesh A. Development: myoblasts (embryonic cells) multinucleate myocytes - syncytium B. Sarcolemma and T-tubules – membranes specialized for electrical impulse conduction a. T-tubules are openings that run congruently with sarcolemma and conduct the initial impulse C. Sarcoplasmic reticulum (SR) – stores calcium a. Enlarged regions near T-tubles: terminal cisternae allow quick communication from membrane to the SR D. Myofibrils – cylindrical structures organized into “ sarcomeres ,” the smallest functional unit a. Thick filaments: myosin b. Thin filaments: actin The Sliding Filament Model of Contraction I. The Sarcomere A. Repeating units of myofilaments within a myofibril containing thick and thin filaments a. (actin – myosin –actin) sandwich b. Actin and myosin myofilaments overlap B. Several regions have named bands or lines a. Sarcomere starts at Z-line (connects actin from adjacent sarcomere) and ends at the next Z-line b. A-band = Myosin (heavy filaments) look d a rk in the microscope c. I-band = Where myosin is absent, the myofibril has a l i ght band d. M-line = In the center, joining myosin/thick myofilaments (middle of H-zone) C. Sliding Filaments (muscle shortens during contraction because they slide into each other across the H-zone)
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a. Tropomyosin is a small, long, thin protein that wraps around actin b. Troponin is a gatekeeper protein that binds to actin and tropomyosin (holds tropomyosin and actin together over the active sites) 1. Calcium binds to troponin, signaling contraction c. When the signal for contraction begins, myosin pulls actin past itself d. The two ends of the sarcomere get shorter II. Control of skeletal muscle contraction A. Neural Excitation of Skeletal Muscle Contraction 1. Neuromuscular Junctions a. Connections between nerves and muscles b. Synaptic terminal (end of axons) sends signal through synapse to the motor end plate c. Acetylcholine (ACh) – the neurotransmitter stored in vesicles i. Production , action potential stimulus for release of Ach.
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Chapter 9 Muscular System - The Muscular System overview I...

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