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Muscle Structure and Function in Anatomy & Physiology

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  • What are fascicles?

    Fascicles are bundles of muscle fibers grouped together within a muscle, surrounded by the perimysium connective tissue.

  • What is sarcoplasm?

    Sarcoplasm is the cytoplasm of a muscle fiber, containing glycogen, myoglobin, and organelles.

  • What is the role of the sarcoplasmic reticulum?

    The sarcoplasmic reticulum stores and releases calcium ions essential for muscle contraction.

  • What are thin and thick filaments?

    Thin filaments are primarily actin, while thick filaments are primarily myosin; both interact to cause muscle contraction.

  • What is a sarcomere?

    A sarcomere is the basic contractile unit of a muscle fiber, defined by Z discs and containing overlapping thin and thick filaments.

  • What happens at the neuromuscular junction?

    The neuromuscular junction is where a motor neuron releases acetylcholine to stimulate muscle fiber depolarization and contraction.

  • What are the events during the contraction cycle?

    The cycle includes calcium binding, cross-bridge formation, power stroke, ATP binding for release, and resetting of myosin heads.

  • Name the three different muscle fiber types.

    Muscle fibers include slow oxidative, fast oxidative, and fast glycolytic types, differing in contraction speed and fatigue resistance.

  • What are synergistic muscle contractions?

    Synergistic contractions occur when muscles work together to produce a movement or stabilize joints.

  • What are different shapes/arrangements of muscles?

    Muscle shapes include parallel, pennate, convergent, circular, and fusiform, affecting force and range of motion.

  • What are the properties of muscle tissue?

    Muscle tissue properties include excitability, contractility, extensibility, and elasticity.

  • Differences between skeletal, cardiac, and smooth muscle?

    Skeletal is voluntary and striated, cardiac is involuntary and striated with intercalated discs, smooth is involuntary and non-striated.

  • What are endomysium, perimysium, and epimysium?

    Connective tissue layers: endomysium surrounds fibers, perimysium surrounds fascicles, epimysium surrounds the entire muscle.

  • What is depolarization vs. repolarization in muscle cells?

    Depolarization is the influx of Na+ causing a positive shift; repolarization restores resting potential by K+ efflux.

  • What is muscle tone?

    Muscle tone is the state of partial contraction that maintains muscle firmness and readiness.

  • Explain the sliding filament theory.

    The sliding filament theory states that thin filaments slide past thick filaments, shortening the sarcomere during contraction.

  • Which sarcomere zones change during contraction?

    The H zone and I band shorten, while the A band remains constant during contraction.

  • What is the role of calcium in muscle contraction?

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

  • How do muscles restore energy?

    Muscles restore energy using creatine phosphate, aerobic respiration, and anaerobic glycolysis.

  • What are motor units?

    A motor unit consists of a motor neuron and all the muscle fibers it innervates.

  • What is aponeurosis?

    Aponeurosis is a broad, flat tendon that connects muscles to bones or other muscles.

  • What criteria are used to name muscles?

    Muscles are named by location, shape, size, direction of fibers, number of origins, and action.

  • Where is calcium stored in muscle cells?

    Calcium is stored in the sarcoplasmic reticulum of muscle fibers.

  • What causes muscle fatigue?

    Muscle fatigue results from ATP depletion, lactic acid buildup, and ionic imbalances.

  • What is the role of acetylcholine in muscle contraction?

    Acetylcholine triggers muscle fiber depolarization by binding to receptors at the neuromuscular junction.

  • What is the role of myoglobin?

    Myoglobin stores oxygen in muscle cells to support aerobic respiration.

  • How does smooth muscle contraction differ?

    Smooth muscle contracts involuntarily using calcium-calmodulin activation of myosin light chain kinase, not troponin.

  • Define fulcrum, lever, load, and effort in muscle movement.

    Fulcrum is the pivot point, lever is the bone, load is the resistance, and effort is the force applied by muscle.