AEMCA Practice Exam

Which phase occurs after the plateau phase in cardiac action potential?

1. Phase 0

2. Phase 3

3. Phase 1

4. Phase 2

The correct answer is: Phase 3

In the cardiac action potential, the plateau phase is primarily represented by Phase 2, during which there is a prolonged depolarization and a balance between the influx of calcium ions and the efflux of potassium ions. Once the plateau phase has ended, the next phase is Phase 3. Phase 3 is characterized by the repolarization of the cardiac cell. This occurs due to the closure of calcium channels and a significant increase in potassium conductance, leading to the outward flow of potassium ions. This causes the membrane potential to decrease back towards the resting membrane potential. Understanding this sequence is crucial, as it reflects the physiological processes underlying the cardiac cycle, influencing how the heart contracts and relaxes. Each phase of the cardiac action potential plays an essential role in ensuring efficient heart function, and recognizing the transition from the plateau to repolarization is fundamental to grasping cardiac physiology.