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Steps of Muscle Contraction quiz #1

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  • What are the main steps involved in the process of muscle contraction from the initial nervous signal to the cessation of contraction?
    Muscle contraction begins when a nerve impulse reaches the neuromuscular junction, causing the release of acetylcholine, which binds to receptors on the muscle fiber's sarcolemma and initiates an action potential. This action potential travels along the sarcolemma and into the T-tubules, triggering the sarcoplasmic reticulum to release calcium ions. Calcium binds to troponin, causing tropomyosin to shift and expose myosin binding sites on actin. Myosin heads then bind to actin, performing the cross-bridge cycle powered by ATP, which shortens the sarcomere. Contraction ends when calcium is reabsorbed into the sarcoplasmic reticulum and acetylcholine is broken down by acetylcholinesterase.
  • How does the action potential lead to the release of calcium ions in muscle fibers, and why is this step important for muscle contraction?
    The action potential travels along the sarcolemma and dives into the T-tubules, which are closely associated with the sarcoplasmic reticulum. This electrical signal triggers voltage-gated channels in the sarcoplasmic reticulum to open, releasing calcium ions into the sarcomere. The release of calcium is crucial because it binds to troponin, causing tropomyosin to move and expose myosin binding sites on actin, enabling the cross-bridge cycle and muscle contraction.
  • Describe the cross-bridge cycle and explain the role of ATP in this process during muscle contraction.
    The cross-bridge cycle starts when the myosin head, energized by hydrolyzed ATP (ADP and phosphate), binds to exposed sites on actin, forming a cross-bridge. The myosin head then performs a power stroke, pulling actin toward the center of the sarcomere and releasing ADP and phosphate. A new ATP molecule binds to the myosin head, causing it to detach from actin. The ATP is then hydrolyzed, re-cocking the myosin head for another cycle. ATP is essential for both detachment and re-energizing the myosin head.
  • What neurotransmitter is released at the neuromuscular junction to initiate muscle contraction?
    Acetylcholine is released at the neuromuscular junction, where it binds to receptors on the muscle fiber's sarcolemma to initiate an action potential.
  • How does the action potential travel from the sarcolemma to the interior of the muscle fiber?
    The action potential propagates along the sarcolemma and dives into the T-tubules, carrying the signal deep into the muscle fiber.
  • What is the role of calcium ions in the process of muscle contraction?
    Calcium ions are released from the sarcoplasmic reticulum and bind to troponin, causing tropomyosin to move and expose myosin binding sites on actin.
  • Describe the sequence of events that leads to the exposure of myosin binding sites on actin.
    Calcium binds to troponin, which causes tropomyosin to shift away from actin, exposing the myosin binding sites and allowing cross-bridge formation.
  • What are the main steps of the cross-bridge cycle during muscle contraction?
    The myosin head binds to actin, performs a power stroke to pull actin, releases ADP and phosphate, detaches when a new ATP binds, and is re-cocked by ATP hydrolysis.
  • How does muscle contraction stop after it has been initiated?
    Muscle contraction stops when calcium is reabsorbed into the sarcoplasmic reticulum and acetylcholine is broken down by acetylcholinesterase, ending the action potential.
  • Why is ATP necessary for both the detachment and re-cocking of the myosin head during the cross-bridge cycle?
    ATP binds to the myosin head to cause its detachment from actin, and its hydrolysis provides the energy needed to re-cock the myosin head for another cycle.
  • What is the role of calcium ions in muscle contraction?
    Calcium ions bind to troponin, causing tropomyosin to shift and expose myosin binding sites on actin filaments, which allows the cross-bridge cycle and muscle contraction to occur.
  • Where are calcium ions stored inside muscle cells?
    Calcium ions are stored in the sarcoplasmic reticulum inside muscle cells.
  • During muscle contraction, calcium ions bind to which protein?
    During muscle contraction, calcium ions bind to troponin.
  • Describe the role of calcium in muscle contraction.
    Calcium initiates muscle contraction by binding to troponin, which moves tropomyosin and exposes myosin binding sites on actin, enabling cross-bridge formation.
  • How does calcium contribute to the process of muscle contraction?
    Calcium is released from the sarcoplasmic reticulum in response to an action potential, binds to troponin, and triggers the exposure of myosin binding sites on actin, allowing contraction.
  • What is the function of calcium during muscle contraction?
    Calcium binds to troponin, causing a conformational change that moves tropomyosin away from actin's binding sites, permitting myosin to attach and initiate contraction.
  • What is a power stroke during muscle contraction?
    A power stroke is the action where the myosin head pulls on the actin filament, moving it toward the center of the sarcomere, which shortens the muscle.
  • What does calcium do in muscle contraction?
    Calcium binds to troponin, leading to the movement of tropomyosin and exposure of myosin binding sites on actin, which is necessary for muscle contraction.
  • What is the effect of calcium during muscle contraction?
    Calcium enables muscle contraction by binding to troponin, which shifts tropomyosin and exposes binding sites for myosin on actin filaments.
  • What is a power stroke in muscle contraction?
    A power stroke is the movement of the myosin head that pulls the actin filament toward the center of the sarcomere, powered by the release of ADP and phosphate.
  • Define the power stroke in the context of muscle contraction.
    The power stroke is the phase in the cross-bridge cycle where the myosin head pivots and pulls the actin filament, resulting in sarcomere shortening.
  • What is tetanus in muscle contraction?
    Tetanus is a sustained muscle contraction resulting from rapid, repeated stimulation that does not allow the muscle to relax between stimuli.
  • What is the role of acetylcholine in skeletal muscle contraction?
    Acetylcholine is the neurotransmitter released at the neuromuscular junction; it binds to receptors on the muscle fiber's sarcolemma, initiating an action potential that leads to muscle contraction.