What describes the relative refractory period?

The relative refractory period refers to a phase in the cardiac action potential when the myocardium has partially recovered from depolarization but still requires a stronger than normal stimulus to cause another depolarization. During this period, while the cardiac cells are not fully excitable, they can still respond to a sufficiently strong stimulus. This is why the correct answer is that a strong impulse can cause depolarization.

The importance of understanding this period lies in its implications for cardiac function and arrhythmias. If a stimulus occurs during the relative refractory period and is strong enough, it can lead to abnormal rhythms or even initiate a new action potential that interrupts the normal rhythm of the heart.

Options that describe the situation inaccurately include those that suggest any impulse, regardless of strength, can trigger depolarization or suggest that depolarization is impossible. Additionally, the option that mentions maintaining a normal heart rate doesn't relate specifically to the characteristics of the relative refractory period, as it focuses instead on overall heart function rather than the electrical properties during this specific phase.