Question

During which phase of the ventricular action potential is the membrane potential closest to the K⁺ equilibrium potential?

(A) Phase 0
(B) Phase 1
(C) Phase 2
(D) Phase 3
(E) Phase 4

Answer 1

During Phase 3 of the ventricular action potential, the membrane potential is closest to the K+ equilibrium potential due to the opening of K+ channels allowing K+ to exit the cell, leading to repolarization. Option (D) Phase 3 is the correct answer.

Step-by-step explanation:

The phase of the ventricular action potential where the membrane potential is closest to the K+ equilibrium potential is Phase 3, also known as the repolarization phase. During Phase 0, there's a rapid influx of Na+, which results in depolarization. Phase 1 is a brief initial repolarization.

Phase 2, the plateau phase, is characterized by the slow inflow of Ca2+ with minimal K+ movement. During Phase 3, K+ channels open widely, allowing an efflux of K+, which brings the membrane potential back towards the K+ equilibrium potential.

Finally, Phase 4 is the resting potential, which is less negative than the K+ equilibrium potential due to the Na+/K+ pump maintaining the cell's baseline state. The correct option for when the membrane potential is closest to the K+ equilibrium potential is therefore (D) Phase 3.