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Muscle Anatomy & Physiology Flashcards

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  • What are the three types of muscle tissue?

    Skeletal, Cardiac, and Smooth muscle.

  • What are the special characteristics of muscle tissue?

    Excitability: respond to stimuli; Contractility: shorten when stimulated; Extensibility: stretchable; Elasticity: recoil to resting length.

  • What connective tissue sheath surrounds the entire skeletal muscle?

    Epimysium, made of dense irregular connective tissue.

  • What connective tissue sheath surrounds fascicles in skeletal muscle?

    Perimysium, made of fibrous connective tissue.

  • What connective tissue sheath surrounds individual muscle fibers?

    Endomysium, made of fine areolar connective tissue.

  • What is the sarcolemma?

    The plasma membrane of a muscle fiber (cell).

  • Describe the structure of a skeletal muscle fiber.

    Elongated, cylindrical cell with multiple peripheral nuclei, many mitochondria, glycosomes, myoglobin, myofibrils, sarcoplasmic reticulum, and T tubules.

  • What is a myofibril?

    Densely packed, rodlike contractile elements making up about 80% of muscle cell volume, showing striations.

  • What defines a sarcomere?

    The region of a myofibril between two successive Z discs, the smallest contractile unit.

  • What proteins make up thick and thin filaments in a sarcomere?

    Thick filaments are made of myosin; thin filaments are made of actin.

  • What is the function of the Z-discs in muscle fibers?

    Z-discs anchor thin filaments and connect adjacent myofibrils.

  • What is the H-zone in a sarcomere?

    The lighter region in the center of the A band where thick and thin filaments do not overlap.

  • What is the M-line?

    The protein myomesin line that holds adjacent thick filaments together in the sarcomere center.

  • What are the two binding sites on myosin heads?

    One site binds to actin and the other binds to ATP.

  • What is the role of tropomyosin in thin filaments?

    Tropomyosin blocks myosin binding sites on actin at rest, regulating contraction.

  • What are the three subunits of troponin and their functions?

    TnI: inhibits contraction by binding actin; TnT: binds tropomyosin; TnC: binds calcium ions.

  • What is the main function of the sarcoplasmic reticulum (SR) in muscle cells?

    Regulates intracellular calcium ion levels essential for contraction.

  • What is a triad in muscle fibers?

    A structure formed by a T-tubule flanked by two terminal cisternae of the SR.

  • How do the sarcoplasmic reticulum, T-tubules, and terminal cisternae work together?

    T-tubules conduct action potentials deep into the fiber, triggering SR to release calcium from terminal cisternae for contraction.

  • What does muscle shortening mean and when does it occur?

    Shortening means sarcomeres shorten as thin filaments slide past thick filaments during contraction.

  • Describe the sliding filament model of muscle contraction.

    Myosin heads bind to actin, pull thin filaments toward the M line, shortening sarcomeres and muscle fibers.

  • What is a neuromuscular junction?

    The synapse between a motor neuron axon terminal and a skeletal muscle fiber's motor end plate.

  • What neurotransmitter is released at the neuromuscular junction and what terminates its effect?

    Acetylcholine (ACh) is released to activate contraction; acetylcholinesterase breaks down ACh to stop contraction.

  • Outline the role of calcium in muscle contraction at low and high intracellular concentrations.

    Low Ca2+: tropomyosin blocks actin sites, muscle relaxes. High Ca2+: Ca2+ binds troponin, moves tropomyosin, allowing cross-bridge cycling.

  • What are the key steps in muscle contraction activation?

    Action potential reaches motor neuron terminal → Ca2+ influx → ACh release → ACh binds receptors → Na+ influx depolarizes muscle membrane.

  • What happens during excitation-contraction coupling?

    Action potential spreads along sarcolemma and T-tubules → triggers Ca2+ release from SR → initiates contraction.

  • Describe the cross-bridge cycle steps.

    1. Cross-bridge formation (myosin binds actin); 2. Power stroke (myosin pulls actin); 3. Cross-bridge detachment (ATP binds myosin); 4. Cocking of myosin head (ATP hydrolysis).

  • What is a motor unit?

    A motor neuron and all the muscle fibers it innervates, contracting together.

  • What are the three phases of a muscle twitch?

    Latent period (excitation-contraction coupling), contraction period (cross-bridge cycling), relaxation period (Ca2+ reuptake).