During the effective refractory period, what is true about depolarization?

During the effective refractory period, cardiac cells are in a state where they cannot be depolarized, regardless of the strength of the incoming impulse. This is a crucial phase of the cardiac action potential, during which cells are recovering from the previous action potential and are unable to respond to new stimuli. Therefore, it is accurate to say that depolarization cannot be initiated by any impulse during this time.

The effective refractory period ensures that the heart has a defined rhythm and prevents dangerous arrhythmias by allowing time for the heart to fully reset and refill with blood before the next contraction. This mechanism is essential for maintaining healthy heart function, as it contributes to the coordinated contractions necessary for effective blood pumping.

Other choices do not reflect the physiological principles governing the effective refractory period. The ability to initiate depolarization, regardless of impulse strength, is a characteristic of other phases but not during the effective refractory period. Similarly, depolarization does not occur as an automatic reset of heart rhythm; it is contingent upon a phase of recovery rather than a predetermined occurrence.