Question

Phase 2 of the cardiac action potential, when the calcium channels remain open and potassium channels are closed, is called the

a) Depolarization phase
b) Repolarization phase
c) Plateau phase
d) Resting phase"

Answer 1

The phase of the cardiac action potential when the calcium channels remain open and potassium channels are closed is the plateau phase.

Step-by-step explanation:

The phase of the cardiac action potential during which calcium channels remain open and potassium channels are closed is known as the plateau phase. This phase follows the rapid depolarization of the cardiac cell's membrane, where the potential rises to about +30 mV before the sodium channels close. The plateau phase is characterized by the steady entry of Ca2+ ions via slow calcium channels, which sustains the cell's depolarized state. It lasts approximately 175 ms and is crucial for the duration of the contraction of the heart muscle, part of the overall sequence of events making up the cardiac cycle. After the plateau phase, the membrane potential eventually reaches zero, at which point the Ca2+ channels close and K+ channels open, leading to repolarization and the return to the resting phase.