After a Muscle Cell Contracts,which of the Following Must Occur

Question

After a muscle cell contracts,which of the following must occur for the muscle to stop contracting?
A) Calcium ions must be pumped back into the endoplasmic reticulum.
B) Calcium ions must flow out of the endoplasmic reticulum.
C) Calcium ions must flow into the muscle cell.
D) Calcium ions must flow out of the muscle cell.
E) Calcium ions must be pumped out of the muscle cell.

Accepted Answer

When a muscle cell contracts, the calcium ions are released from the sarcoplasmic reticulum into the cytoplasm, leading to the interaction of actin and myosin filaments which causes contraction. In order for the muscle to stop contracting, the calcium ions must be removed from the cytoplasm. This is achieved through the action of calcium ATPase pumps, which actively transport calcium ions back into the sarcoplasmic reticulum. Therefore, choice A (calcium ions must be pumped back into the endoplasmic reticulum) is the correct answer.