CVS Practice Test 2025 – Complete Exam Preparation

The sarcoplasmic reticulum (SR) plays a crucial role in regulating calcium levels in muscle cells following an action potential. The correct choice indicates that the SR sequesters calcium with the action of the SERCA pump, which stands for sarcoplasmic reticulum calcium ATPase. This mechanism is essential for muscle relaxation after contraction.

When a muscle cell is activated and an action potential occurs, calcium ions are released from the SR into the cytoplasm, which triggers muscle contraction. After the contraction, it is necessary for the muscle to relax, which is where SERCA comes into play. SERCA uses ATP to pump calcium ions back into the SR, effectively lowering the cytoplasmic concentration of calcium and allowing the muscle fibers to return to a relaxed state. This process is vital for ensuring that muscle contractions are transient and that the muscle can be prepared for subsequent contractions.

In contrast, other methods mentioned in the options do not accurately reflect the primary function of the SR. The release of more calcium, inhibition of calcium channels, or releasing calcium into the bloodstream are not the primary mechanisms for calcium regulation by the SR after an action potential. Instead, the efficient sequestration of calcium by SERCA is the correct and most critical function in this context