Lecture 15: Muscle Physiology Reading: chapter 8, section: skeletal muscle, pgs 253-259 (pgs 257-263, if using 5thedition) Types of Muscle (3types) skeletal muscle– striated, voluntary cardiac muscle– striated, involuntarysmooth muscle– unstriated, involuntarySkeletal 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 (Figure 8-2)Muscle- population of elongated muscle fibersheld together by connective tissue and connected at either end by tendons (Figure 8-3). Muscle Fiber- single, multinucleated cell composed of a population of elongated myofibrils. Myofibril- elongated, cylindrically-shaped contractile elements composed of a population of sarcomeresconnected end-to-end (Figure 8-4). Sarcomere- the smallest unit of a muscle cell containing all of the elements necessary for contraction. Composed of interdigitating and partially-overlapping thickand thin filaments. Structural components - Z line - region where thin filaments from adjacent sarcomeres join - A band- region with thick filaments
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