Multiple Choice
Which of the following steps of the crossbridge cycle occurs immediately before the power stroke?
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9. Muscle Tissue
Steps of Muscle Contraction
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Which of the following correctly lists the steps of muscle fiber contraction in the proper sequence?
A
Acetylcholine is released, action potential arrives at the neuromuscular junction, myosin binds to actin, calcium ions are released from the sarcoplasmic reticulum, muscle fiber contracts.
B
Myosin binds to actin, acetylcholine is released, action potential arrives at the neuromuscular junction, calcium ions are released from the sarcoplasmic reticulum, muscle fiber contracts.
C
Action potential arrives at the neuromuscular junction, acetylcholine is released, calcium ions are released from the sarcoplasmic reticulum, myosin binds to actin, muscle fiber contracts.
D
Calcium ions are released from the sarcoplasmic reticulum, action potential arrives at the neuromuscular junction, acetylcholine is released, myosin binds to actin, muscle fiber contracts.
Verified step by step guidance1
Step 1: Understand the sequence of events in muscle fiber contraction. Muscle contraction begins with an action potential traveling down a motor neuron to the neuromuscular junction.
Step 2: At the neuromuscular junction, the arrival of the action potential triggers the release of acetylcholine, a neurotransmitter, into the synaptic cleft.
Step 3: Acetylcholine binds to receptors on the muscle fiber's sarcolemma, leading to depolarization and the generation of an action potential in the muscle fiber.
Step 4: The action potential travels along the sarcolemma and down the T-tubules, causing the sarcoplasmic reticulum to release calcium ions into the cytoplasm of the muscle fiber.
Step 5: Calcium ions bind to troponin, causing a conformational change that moves tropomyosin away from the binding sites on actin. This allows myosin heads to bind to actin, initiating the cross-bridge cycle and muscle contraction.
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