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