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Skeletal Muscle Physiology Lecture 1 Skeletal Muscle Characteristics and Functions Characteristics: • Multinucleated (peripheral nuclei) • Striated • Voluntary • Covers bony skeleton • Motor fibers that contract rapidly/vigorously, tires easily, exerts great force Functions: • Movement • Posture • Heat Generation • Support • Respiration • Communication • Constriction of organs and vessels • Heart beat • Excitability, Contractility, Extensibility, Elasticity Parts of Skeletal Muscle • Skeletal Muscle – contains muscle fibers, CT, blood vessels, nerves; developed from myoblasts • Muscle fiber – one muscle cell; single cells; multinucleated; sarcolemma surrounds muscle fiber • Epimysium – layer of dense CT around skeletal muscle (contains bundle of muscle fibers called fascicle) • Perimysium – second layer of collagen CT around fascicles • Endomysium – thin delicate layer of CT around muscle fiber contained in a fascicle Parts of Skeletal Muscle • Myofibrils – resides inside a muscle fiber; contractile factor; sarcoplasm surrounds myofibrils • Myofilament – resides inside a myofibril; Myosin (thick) and Actin (thin) • Sarcolemma – cell membrane of the muscle fiber • Sarcoplasm – cytoplasm of a muscle cell; spaces between the myofibrils that are filled with intracellular fluid; contains K, Mg, P, protein enzymes, and mitochondria supplying myofibrils with ATP • Sarcoplasmic Reticulum – inside the sarcoplasm surrounding myofibrils which controls muscle contraction; consists of sarcomere • Sequence of Layers: Fascia Skeletal Muscle Epimysium Perimysium Endomysium Fascicles Muscle Fiber(Endomysium around entire muscle fiber) Sarcolemma(cell membrane of muscle fiber) Myofibril Sarcoplasm(cytoplasm between myofibrils) Myofilament(actin & myosin) Inside a Muscle Fiber- Myofibrils • • • • • • Thick protein myofilaments - Myosin Thin protein myofilaments – Actin Striations are caused by arrangement of thick and thin myofilaments Sarcomere – Z line/disc to Z line/disc; contractile unit of a myofibril A band = dark area (thick + thin) M line = connects central portion of each thick filament to its neighbors; stabilizes thick filaments • H zone = lighter region on either side of M line in resting sarcomere; contains only THICK myofilaments • I band = light area; thin only • Titin = an elastic filament that extends from Z disc to the thick filament and attaches to M line Myofilaments • Thick Filaments = myosin • Rod like tail (axis) that terminates in two globular heads or cross bridges • Head region site of Myosin ATPase activity (Breaks down ATP, releases energy) • Thin Filaments = actin • Helical structure tethered at one end at the Z disc • G-actin (globular form of actin) • F-actin (filaments actin formed from g-actin) • Tropomyosin • Rod-shaped protein spiraling around actin and prevents attachment of cross-bridges • Troponin complex • Complex of polypeptides • Tropomyosin and Troponin help control actin’s interaction with myosin during contraction Links • Khan Academy: Skeletal Muscle (YouTube) • • • • Anatomy of Muscle Actin and Myosin Tropomyosin and Troponin Sarcoplasmic Reticulum • Biology Medicine Animation: Skeletal Muscle (YouTube) • *To find links to videos- view PowerPoint in presentation mode and click on hyperlink (title that is underlined) it will open up internet webpage for viewing