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Unformatted text preview: Lecture 15: Muscle Physiology Reading: chapter 8, section: skeletal muscle, pgs 257-264 (pgs 253-259, if using 6 th edition) (pgs 257-263, if using 5 th edition) Types of Muscle (3 types) skeletal muscle striated, voluntary cardiac muscle striated, involuntary smooth muscle unstriated, involuntary Skeletal Muscle Neuromuscular Junction, sequence of events: 1) Action potential propagates into the presynaptic terminal 2) Depolarization of the presynaptic terminal opens voltage-gated Ca ++ channels 3) Ca ++ ions trigger vesicles of Ach to fuse with the plasma membrane 4) ACh diffuses across the synaptic cleft and binds with receptors in the motor endplate 5) ACh binding with the receptor leads to the opening of cation channels. Na ++ enters and depolarizes the end plate (EPP) 6) Depolarizing current flows to adjacent membrane that contains voltage-gated Na ++ channels (action potential) 7) Ach is degraded by Ach-esterase, terminating the action of ACh Skeletal Muscle Organization Muscle- population of elongated muscle fibers held together by connective tissue and connected at either end by tendons ) . Muscle Fiber- single, multinucleated cell composed of a population of elongated myofibrils . Myofibril- elongated, cylindrically-shaped contractile elements composed of a population of sarcomeres connected end-to-end. Sarcomere- the smallest unit of a muscle cell containing all of the elements necessary for contraction. Composed of interdigitating and partially-overlapping thick and thin filaments . Structural components - Z line - region where thin filaments from adjacent sarcomeres join - A band- region with thick filaments - I band- region without thick filaments - H zone- region without thin filaments - M line- region in the center of the thick filaments Thick Filament- special assemblies of hundreds of myosin protein molecules organized into elongated fibers. Myosin- cytoskeletal protein composed of two interwoven subunits, each with a long tail and a globular head region. actin binding site- specialized region of the myosin head capable of binding to actin . myosin ATPase- specialized region of the myosin head capable of ATP hydrolysis. Thin Filament- specialized assemblies of three proteins, actin, tropomyosin and troponin , arranged to form an elongated double helical strand. Actin- Globular cytoskeletal protein linked to form two long chains arranged in a double helical strand. Tropomyosin- pairs of threadlike filamentous proteins that lie alongside the groove formed by the actin helix. Troponin- protein complex composed of three subunits, one that binds to actin, one that binds to tropomyosin, and one that binds Ca ++ . Multiple copies of this complex are bound to the strands of actin and tropomyosin....
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This note was uploaded on 01/29/2012 for the course NPB 101 taught by Professor Fuller,charles/goldberg,jack during the Winter '08 term at UC Davis.
- Winter '08