AEMCA Practice Exam

Which phase refers to rapid depolarization in the cardiac action potential?

1. Phase 1

2. Phase 2

3. Phase 0

4. Phase 4

The correct answer is: Phase 0

The phase that refers to rapid depolarization in the cardiac action potential is indeed the correct choice. During this phase, there is a swift influx of sodium ions (Na+) into the cardiac muscle cells, which causes the membrane potential to become more positive. This rapid change in voltage is typically marked by the opening of voltage-gated sodium channels. As these channels open, the permeability of the cell membrane to sodium increases dramatically, leading to a sharp increase in the membrane potential and initiating the depolarization phase of the action potential. Understanding this specific phase is crucial as it sets the stage for the subsequent events in the cardiac action potential, including the plateau and repolarization phases, which are essential for the proper timing of cardiac contractions and the overall function of the heart.