During which period can a stronger than normal impulse stimulate depolarization?

During which period can a stronger than normal impulse stimulate depolarization?

• A. Absolute refractory period
• B. Relative refractory period
• C. Normal excitability period
• D. Depolarization period

Answer: (B)

The relative refractory period is the correct choice because it is the phase following the absolute refractory period during which a stronger-than-normal stimulus can lead to depolarization of the cardiac cells. This period occurs because, while some sodium channels are still inactive, others are transitioning back to a state where they can be activated. Therefore, if the stimulus is sufficiently strong, it can cause depolarization by triggering these channels. During the absolute refractory period, the cardiac muscle cells cannot be depolarized regardless of the strength of the stimulus, as the sodium channels remain closed and inactive. The normal excitability period, while it indicates a state of readiness to respond to stimuli, does not specifically denote a point where a stronger impulse can cause depolarization. The depolarization period is the phase when depolarization is actively occurring, and it does not correspond to the ability of a stronger stimulus to induce further depolarization, as this is typically already ongoing.

The relative refractory period is the correct choice because it is the phase following the absolute refractory period during which a stronger-than-normal stimulus can lead to depolarization of the cardiac cells. This period occurs because, while some sodium channels are still inactive, others are transitioning back to a state where they can be activated. Therefore, if the stimulus is sufficiently strong, it can cause depolarization by triggering these channels.

During the absolute refractory period, the cardiac muscle cells cannot be depolarized regardless of the strength of the stimulus, as the sodium channels remain closed and inactive. The normal excitability period, while it indicates a state of readiness to respond to stimuli, does not specifically denote a point where a stronger impulse can cause depolarization. The depolarization period is the phase when depolarization is actively occurring, and it does not correspond to the ability of a stronger stimulus to induce further depolarization, as this is typically already ongoing.