Which of the Following Normally Terminates Muscle Contraction

Question

Which of the following normally terminates muscle contraction?
A) Depletion of ACh in the neuromuscular junction
B) Binding of ACh to the NM receptors
C) Pumping of calcium back into the sarcoplasmic reticulum
D) Depletion of ATP within the sarcomere

Accepted Answer

During muscle contraction, calcium ions are released from the sarcoplasmic reticulum and bind to troponin, which causes a conformational change that allows myosin to bind to actin and initiate muscle contraction. When the action potential ends, calcium is actively transported back into the sarcoplasmic reticulum by calcium pumps. As calcium concentration decreases, the troponin-tropomyosin complex re-establishes its blocking position on the actin, preventing further interaction with myosin and thereby ending muscle contraction.