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Muscle Tissue and Contraction - Anatomy & Physiology

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  • Types of muscle tissue

    The three types are skeletal, cardiac, and smooth muscle.

  • Muscle fibers

    Elongated muscle cells found in skeletal and smooth muscle, but not in cardiac muscle.

  • Sarcolemma and sarcoplasm

    Sarcolemma is the plasma membrane of muscle cells; sarcoplasm is the cytoplasm of muscle cells.

  • Key features of skeletal muscle

    Skeletal muscle is striated, voluntary, and responsible for body mobility.

  • Key features of cardiac muscle

    Cardiac muscle is striated, involuntary, and found only in the heart.

  • Key features of smooth muscle

    Smooth muscle is nonstriated, involuntary, and found in walls of hollow organs.

  • Four special characteristics of muscle tissue

    Excitability, contractility, extensibility, and elasticity.

  • Functions of muscle tissue

    Produce movement, maintain posture, stabilize joints, and generate heat.

  • Connective tissue sheaths of skeletal muscle

    Epimysium surrounds whole muscle, perimysium surrounds fascicles, endomysium surrounds individual fibers.

  • Direct vs indirect muscle attachments

    Direct attachments fuse epimysium to bone periosteum; indirect use tendons or aponeuroses.

  • Skeletal muscle fiber size and nuclei

    Fibers are long cylindrical cells, 10-100 μm diameter, up to 30 cm long, with multiple nuclei beneath sarcolemma.

  • Sarcoplasm contents important for contraction

    Contains glycosomes (glycogen storage) and myoglobin (oxygen storage).

  • Myofibrils

    Rodlike structures in muscle fibers made of sarcomeres; account for ~80% of cell volume.

  • Striations in muscle fibers

    Alternating dark A bands and light I bands aligned along myofibrils.

  • Sarcomere

    Smallest contractile unit of muscle fiber, between two Z discs, about 2 μm long.

  • Thick and thin myofilaments

    Thick filaments contain myosin; thin filaments contain actin, tropomyosin, and troponin.

  • Role of titin in muscle

    Titin is an elastic filament that stabilizes thick filaments and helps muscle recoil after stretching.

  • Dystrophin function

    Dystrophin links thin filaments to sarcolemma proteins, stabilizing muscle fiber structure.

  • Sarcoplasmic reticulum (SR)

    Specialized smooth ER that stores and releases calcium ions to trigger muscle contraction.

  • T tubules

    Invaginations of sarcolemma that conduct action potentials deep into muscle fibers, triggering calcium release.

  • Triad in muscle fiber

    Structure formed by a T tubule flanked by two terminal cisterns of the SR, coordinating contraction signals.

  • Sliding filament model

    During contraction, thin filaments slide past thick filaments, shortening sarcomeres without changing filament length.

  • Changes in sarcomere during contraction

    I bands and H zones shorten; A bands length stays the same; Z discs move closer.

  • Excitation-contraction coupling

    Sequence where an action potential triggers calcium release, leading to myofilament sliding and muscle contraction.

  • Role of calcium in contraction

    Calcium binds to troponin, causing tropomyosin to move and expose myosin-binding sites on actin.

  • Cross bridge cycle

    Myosin heads bind actin, pivot, detach using ATP, and reattach to pull thin filaments during contraction.

  • Rigor mortis cause

    After death, ATP depletion prevents cross bridge detachment, causing muscle stiffness.

  • Duchenne muscular dystrophy (DMD)

    Genetic disease caused by defective dystrophin, leading to muscle degeneration and weakness.