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Muscular System - Anatomy & Physiology

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Termini in questo insieme (29)

  • Three types of muscle tissue

    Skeletal muscle: voluntary, striated, attached to bones/skin.
    Cardiac muscle: involuntary, striated, found only in heart.
    Smooth muscle: involuntary, non-striated, found in walls of hollow organs.

  • Four main characteristics of muscle tissue

    Excitability: respond to stimuli.
    Contractility: shorten forcibly.
    Extensibility: stretch.
    Elasticity: recoil to resting length.

  • Functions of muscle

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

  • Connective tissue sheaths of skeletal muscle

    Epimysium: surrounds entire muscle.
    Perimysium: surrounds fascicles.
    Endomysium: surrounds individual muscle fibers.

  • Difference between origin and insertion

    Origin: attachment to immovable or less movable bone.
    Insertion: attachment to movable bone.

  • Structure and function of myofibrils

    Rod-like elements in muscle fibers containing sarcomeres, responsible for striations and contraction.

  • Sarcomere

    Smallest contractile unit of muscle fiber, extends from one Z disc to the next, contains overlapping thick and thin filaments.

  • Composition of thick and thin filaments

    Thick filaments: myosin protein with heads that form cross bridges.
    Thin filaments: actin protein with regulatory proteins tropomyosin and troponin.

  • Role of sarcoplasmic reticulum (SR)

    Stores and releases Ca2+ ions to regulate muscle contraction.

  • Function of T tubules

    Transmit action potentials deep into muscle fiber to trigger Ca2+ release from SR.

  • Sliding filament model of contraction

    Thin filaments slide past thick filaments, increasing overlap without changing filament length, causing sarcomere shortening.

  • Four steps of cross bridge cycling

    1. Cross-bridge formation
    2. Power stroke
    3. Cross-bridge detachment
    4. Cocking of myosin head using ATP energy.

  • Events at the neuromuscular junction

    AP arrives, Ca2+ enters axon terminal, ACh released, binds to receptors, Na+ enters muscle fiber, generating end plate potential.

  • Phases of action potential in muscle fiber

    1. End plate potential (local depolarization)
    2. Depolarization (AP generation)
    3. Repolarization (restoration of resting state).

  • Excitation-contraction coupling

    AP travels along sarcolemma and T tubules, triggers Ca2+ release from SR, Ca2+ binds troponin, exposing myosin binding sites on actin.

  • Muscle twitch phases

    Latent period (E-C coupling), contraction period (cross bridge formation), relaxation period (Ca2+ reentry into SR).

  • All-or-none principle in muscle fibers

    Once stimulated, a muscle fiber contracts fully; no partial contractions occur at the fiber level.

  • Graded muscle responses

    Varying contraction strength by changing stimulus frequency (temporal summation) and stimulus strength (recruitment).

  • Muscle tone

    Constant, slight contraction of muscles maintained by spinal reflexes to keep muscles firm and ready.

  • Sources of ATP for muscle contraction

    Direct phosphorylation by creatine phosphate, anaerobic glycolysis, and aerobic respiration.

  • Creatine phosphate role

    Donates phosphate to ADP to rapidly regenerate ATP for about 15 seconds of muscle activity.

  • Anaerobic glycolysis

    Breakdown of glucose to pyruvic acid without oxygen, producing 2 ATP and lactic acid.

  • Aerobic respiration

    Oxygen-dependent ATP production in mitochondria, producing most ATP during rest and moderate exercise.

  • Causes of muscle fatigue

    Ionic imbalances (K+, Ca2+, Pi), damage to SR, rarely lack of ATP except in severe stress.

  • Factors affecting force of muscle contraction

    Number of fibers stimulated, fiber size, frequency of stimulation, and degree of muscle stretch.

  • Types of skeletal muscle fibers

    Slow oxidative (fatigue resistant), fast oxidative (moderate fatigue), fast glycolytic (fatigue quickly).

  • Effect of load on contraction

    Greater load decreases contraction speed and duration.

  • Motor unit

    A motor neuron and all the muscle fibers it innervates; smaller units allow finer control.

  • Rigor mortis explanation

    Postmortem muscle stiffness due to increased Ca2+ and lack of ATP, causing cross bridges to remain attached.