During repolarization, the heart muscle relaxes.

During repolarization, the heart muscle relaxes.

• A. Contraction
• B. Relaxation
• C. No change
• D. Depolarization.

Answer: (B)

Repolarization is the electrical reset that follows the contraction-triggering depolarization, and it is coupled to the heart muscle relaxing. As the membrane potential returns toward its resting level, calcium is removed from the cytosol—pumped back into the sarcoplasmic reticulum and expelled from the cell—and the intracellular calcium concentration falls. With less calcium available, the myofilaments detach from actin, cross-bridges release, and tension declines. That drop in tension is what we experience as relaxation during diastole. Contraction happens during depolarization when calcium enters the cells and initiates the contractile process, so repolarization leading to relaxation is the correct pairing. A state of no change wouldn’t reflect the normal cycle, and depolarization is the preceding electrical event that starts contraction, not the relaxation phase.

Repolarization is the electrical reset that follows the contraction-triggering depolarization, and it is coupled to the heart muscle relaxing. As the membrane potential returns toward its resting level, calcium is removed from the cytosol—pumped back into the sarcoplasmic reticulum and expelled from the cell—and the intracellular calcium concentration falls. With less calcium available, the myofilaments detach from actin, cross-bridges release, and tension declines. That drop in tension is what we experience as relaxation during diastole. Contraction happens during depolarization when calcium enters the cells and initiates the contractile process, so repolarization leading to relaxation is the correct pairing. A state of no change wouldn’t reflect the normal cycle, and depolarization is the preceding electrical event that starts contraction, not the relaxation phase.