Lecture 23: Muscle Physiology Reading: chapter 8, section: skeletal muscle, pgs 257-264 (pgs 253-259, if using 6thedition) (pgs 257-263, if using 5thedition) Types of Muscle (3 types) skeletal muscle– striated, voluntary cardiac muscle– striated, involuntarysmooth muscle– unstriated, involuntary Skeletal Muscle OrganizationMuscle- population of elongated muscle fibersheld 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 sarcomeresconnected 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 thickand 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 myosinprotein 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 andtroponin, arranged to form an elongated double helical strand. Actin- Globular cytoskeletal protein linked to form two long chains arranged in a double helical strand.
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