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MDCAT Biology QUESTION #4304
Question 1
Once an action potential reaches the membrane of a skeletal muscle fiber, what is the first event in the contraction process?
  • Actin and myosin form a cross-bridge
  • Calcium is pumped back into the sarcoplasmic reticulum
  • Calcium is released from the sarcoplasmic reticulum✔️
  • ATP is hydrolyzed by troponin
Correct Answer Explanation
When an action potential arrives, it triggers the sarcoplasmic reticulum to release $Ca^{2+}$ ions, which bind to troponin, moving tropomyosin and allowing cross-bridge formation.