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Muscle Structure and Contraction - Anatomy & Physiology

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Termini in questo insieme (21)

  • Three types of muscle tissue
    Skeletal, cardiac, and smooth muscle differ in structure, location, function, and activation.
  • Muscle fiber
    An elongated muscle cell, also called a muscle fiber, found in skeletal and smooth muscle.
  • Connective tissue sheaths in skeletal muscle
    Endomysium surrounds each muscle fiber, perimysium surrounds fascicles, and epimysium surrounds the entire muscle.
  • Sarcomere
    The smallest contractile unit of muscle, between two Z discs, composed of thick (myosin) and thin (actin) filaments.
  • Thick filaments composition
    Composed of myosin molecules, each with a rodlike tail and two globular heads that form cross bridges.
  • Thin filaments composition
    Primarily composed of actin with regulatory proteins tropomyosin and troponin bound to actin.
  • Role of calcium in muscle contraction
    Calcium binds to troponin, causing tropomyosin to move and expose myosin binding sites on actin, enabling contraction.
  • Sarcoplasmic reticulum (SR)
    A smooth ER that stores and regulates intracellular calcium, surrounding each myofibril and forming terminal cisternae.
  • T tubules function
    Invaginations of the sarcolemma that conduct action potentials deep into muscle fibers, triggering Ca2+ release from SR.
  • Sliding filament model
    Thin filaments slide past thick filaments, shortening sarcomeres and causing muscle contraction.
  • Neuromuscular junction
    Synapse between a motor neuron axon terminal and a muscle fiber's motor end plate where acetylcholine is released.
  • Acetylcholine (ACh) role
    Binds to receptors on the sarcolemma, opening Na+ channels, causing depolarization and initiating muscle action potential.
  • Excitation-contraction coupling
    Process linking muscle action potential to contraction via Ca2+ release from SR and exposure of actin binding sites.
  • Cross bridge cycle
    Myosin heads attach to actin, pivot to pull thin filaments, detach with ATP binding, and reset for another cycle.
  • Motor unit
    A motor neuron and all the muscle fibers it innervates; size varies with muscle function.
  • Muscle twitch phases
    Latent period (excitation-contraction coupling), contraction period (cross bridge activity), and relaxation period (Ca2+ reuptake).
  • Graded muscle responses
    Variations in contraction strength achieved by changing stimulus frequency or strength (recruitment).
  • Isotonic vs isometric contraction
    Isotonic: muscle changes length and moves load; Isometric: muscle tension increases without length change.
  • Sources of ATP for muscle contraction
    ATP is regenerated by creatine phosphate, anaerobic glycolysis, and aerobic respiration.
  • Muscle fatigue causes
    ATP deficit, lactic acid buildup, and ionic imbalances leading to inability to contract.
  • Muscle tone
    Constant, slight contraction of muscles maintained by spinal reflexes to keep muscles firm and ready.