CVS Practice Test 2026 - Free CVS Practice Questions and Study Guide

During phase 1 of the non-pacemaker action potential, the sodium channels, which are responsible for the influx of Na+ ions, close. This phase is characterized by a rapid repolarization that follows the initial spike in membrane potential caused by the previous opening of sodium channels during phase 0.

As the membrane potential begins to decline, the inactivation of the Na+ channels is crucial for the action potential's return to a resting state. The closure of these channels prevents further influx of sodium, contributing to the overall repolarization process as potassium channels open and potassium ions exit the cell, further driving the membrane potential back towards its resting state.

Understanding this mechanism is vital, as it underscores the sequential and tightly regulated nature of ion channel activity during the action potential phases, which is essential for proper cardiac function and the propagation of electrical signals in cardiac tissue.