Multiple Choice
Which of the following correctly lists the steps of muscle fiber contraction in the proper sequence?
9. Muscle Tissue
Steps of Muscle Contraction
Multiple Choice
In the steps of skeletal muscle contraction, what is the primary role of released from the sarcoplasmic reticulum?
A
It binds to troponin, causing tropomyosin to move and expose myosin-binding sites on actin
B
It binds directly to myosin heads to provide the energy for the power stroke
C
It prevents ATP from binding to myosin, maintaining the rigor state
D
It activates acetylcholinesterase to terminate the signal at the neuromuscular junction
Verified step by step guidance1
Understand that during skeletal muscle contraction, calcium ions (Ca^{2+}) are released from the sarcoplasmic reticulum into the cytoplasm of the muscle fiber.
Recognize that the primary role of Ca^{2+} is to bind to the regulatory protein troponin, which is located on the thin filament (actin).
When Ca^{2+} binds to troponin, it induces a conformational change that causes tropomyosin, another regulatory protein, to shift its position on the actin filament.
This movement of tropomyosin exposes the myosin-binding sites on actin, allowing the myosin heads to attach and initiate the cross-bridge cycle necessary for muscle contraction.
Note that Ca^{2+} does not bind directly to myosin heads, prevent ATP binding, or activate acetylcholinesterase; its key function is to regulate the exposure of binding sites on actin through troponin.
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