Once an action potential reaches the membrane of a skeletal muscle fiber, what is the first event that occurs in the contraction process?
- A. Actin and myosin form a cross-bridge
- B. Calcium is pumped back into the sarcoplasmic reticulum
- C. Calcium is released from the sarcoplasmic reticulum
- D. ATP is hydrolyzed by troponin
Explanation
The action potential travels down the T tubules and triggers the sarcoplasmic reticulum to release calcium, which then binds troponin and moves tropomyosin off the binding sites so cross bridges can form. Cross bridge formation therefore comes second, not first, which is the trap in the first option. Pumping calcium back is what ends the contraction.
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