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Muscle Tissue and Contraction - Anatomy & Physiology

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  • Types of muscle tissue in the body

    There are three types: skeletal muscle, cardiac muscle, and smooth muscle.

  • Functions of skeletal muscle

    Skeletal muscles enable movement, stabilize body position, help maintain body temperature, control voluntary actions like swallowing, and support soft tissues.

  • Connective tissue layers of skeletal muscle

    Three layers: epimysium (outermost, dense collagen), perimysium (surrounds fascicles), and endomysium (surrounds individual muscle fibers).

  • What is a fascicle?

    A fascicle is a bundle of muscle fibers surrounded by the perimysium.

  • Role of satellite cells in muscle tissue

    Satellite cells are stem cells involved in muscle tissue repair.

  • Skeletal muscle fiber characteristics

    They are large, multinucleate cells with multiple nuclei to support high protein production for contraction.

  • Names for skeletal muscle fiber components

    Plasma membrane: sarcolemma, cytoplasm: sarcoplasm, smooth ER: sarcoplasmic reticulum (SR).

  • Myofibrils and myofilaments

    Myofibrils are cylindrical structures inside muscle fibers made of myofilaments: thin (actin) and thick (myosin) filaments.

  • Sarcomere structure

    The sarcomere is the functional unit of muscle fibers, composed of thick and thin filaments plus regulatory proteins troponin and tropomyosin.

  • What causes the striated appearance of skeletal muscle?

    The size, density, and distribution of actin and myosin filaments create the striated or banded pattern.

  • Neuromuscular junction (NMJ) function

    The NMJ is where a muscle fiber receives motor neuron signals to initiate contraction.

  • Membrane potential in muscle cells

    Muscle cells have an electrical gradient across their membrane, typically between -60 to -90 mV, used to generate electrical signals.

  • Role of acetylcholine (ACh) at the NMJ

    ACh is released from the motor neuron, binds to receptors on the sarcolemma, opening ion channels and generating a muscle action potential.

  • Excitation-contraction coupling

    Action potentials spread along the sarcolemma and into T-tubules, triggering Ca2+ release from the sarcoplasmic reticulum.

  • Role of calcium ions in muscle contraction

    Ca2+ binds to troponin, causing tropomyosin to move and expose active sites on actin for myosin binding.

  • Function of troponin and tropomyosin

    Tropomyosin blocks actin active sites at rest; troponin binds calcium and moves tropomyosin to allow contraction.

  • Myosin head state in resting muscle

    Myosin heads are cocked and ready for contraction, having hydrolyzed ATP to ADP and Pi.

  • Cross-bridge formation

    Myosin heads bind to exposed active sites on actin, forming cross-bridges essential for contraction.

  • Power stroke in muscle contraction

    Release of ADP and Pi causes myosin heads to pivot, pulling actin filaments toward the sarcomere center.

  • Role of ATP in muscle contraction cycle

    ATP binding causes myosin to detach from actin; ATP hydrolysis recocks the myosin head for another cycle.

  • Sliding filament model

    During contraction, thin filaments slide past thick filaments, shortening sarcomeres and muscle fibers.

  • ATP sources for muscle contraction

    ATP is generated via creatine phosphate, glycolysis, and aerobic respiration.

  • Creatine phosphate role

    Creatine phosphate donates phosphate to ADP to rapidly regenerate ATP during initial muscle contraction.

  • Glycolysis in muscle cells

    Glycolysis breaks down glucose anaerobically to produce 2 ATP and 2 pyruvate molecules.

  • Aerobic respiration efficiency

    Aerobic respiration produces about 17 ATP per pyruvate, making it more efficient than glycolysis.

  • Lactic acid formation during intense exercise

    When oxygen is low, pyruvate converts to lactic acid, which is transported to the liver for glucose regeneration (Cori Cycle).