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Skeletal Muscle Tissue Structure and Contraction

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이 집합의 용어 (20)

  • What are the main functions of skeletal muscle tissue?
    Movement, posture maintenance, body temperature regulation, and guarding body entrances/exits (sphincters).
  • Describe the general structure of a skeletal muscle fiber.
    Long, cylindrical, multinucleated cells with striations, containing myofibrils made of thin (actin) and thick (myosin) filaments.
  • What is a sarcomere and what are its key components?
    The sarcomere is the functional contractile unit of muscle, composed of thin filaments, thick filaments, Z lines, M line, A band, I band, and H zone.
  • What changes occur in the sarcomere during muscle contraction?
    The H zone and I band shorten, the A band remains the same length, and thin filaments slide over thick filaments.
  • What role does the neuromuscular junction play in muscle contraction?
    It transmits the nerve impulse to the muscle fiber, releasing acetylcholine (ACh) to trigger an action potential.
  • How does acetylcholine (ACh) initiate muscle contraction?
    ACh binds to receptors on the sarcolemma, opening Na+ channels and generating an action potential.
  • What happens to acetylcholine after it triggers an action potential?
    It is broken down by acetylcholinesterase (AChE) to stop the signal and allow muscle relaxation.
  • Describe the role of calcium ions (Ca2+) in muscle contraction.
    Ca2+ binds to troponin, causing tropomyosin to move and expose active sites on actin for myosin binding.
  • What is the function of troponin and tropomyosin in muscle fibers?
    Troponin binds Ca2+ to move tropomyosin, which blocks or exposes active sites on actin for contraction control.
  • Explain the cross-bridge cycle in muscle contraction.
    Myosin heads bind to actin active sites, pivot to pull filaments (power stroke), detach with ATP, and reactivate for another cycle.
  • What is the source of energy for muscle contraction?
    ATP hydrolysis provides energy for myosin head movement and detachment during the contraction cycle.
  • How do muscle fibers develop during growth?
    Muscle fibers form by fusion of myoblasts into multinucleated myotubes that mature into muscle fibers.
  • What is the role of the sarcoplasmic reticulum in muscle contraction?
    It stores and releases Ca2+ ions in response to action potentials to regulate contraction.
  • What is the function of T tubules in skeletal muscle fibers?
    T tubules transmit action potentials deep into the muscle fiber to trigger Ca2+ release from the sarcoplasmic reticulum.
  • What is Duchenne Muscular Dystrophy (DMD)?
    A severe X-linked recessive disorder causing muscle wasting due to absence of dystrophin, leading to muscle damage and weakness.
  • How does the absence of dystrophin affect muscle fibers in DMD?
    Without dystrophin, muscle fibers are damaged during contraction, causing progressive muscle degeneration.
  • What is the typical prognosis for individuals with Duchenne Muscular Dystrophy?
    Most become wheelchair-dependent by age 12, with median life expectancy of 20-30 years due to cardiac or respiratory failure.
  • What structural features distinguish skeletal, cardiac, and smooth muscle tissues?
    Skeletal: long, cylindrical, multinucleated, striated; Cardiac: short, branched, striated, intercalated discs; Smooth: short, spindle-shaped, nonstriated.
  • What is the role of titin in the sarcomere?
    Titin stabilizes thick filaments and provides elasticity, helping sarcomeres return to resting length after contraction.
  • What happens during the power stroke in muscle contraction?
    Myosin heads pivot, pulling thin filaments toward the M line, shortening the sarcomere and generating tension.