Biological Systems MCAT Practice Exam 2025 – The Comprehensive All-in-One Guide for Exam Success!

During repolarization, the K+ channels play a crucial role in restoring the membrane potential after depolarization. When an action potential is generated, voltage-gated Na+ channels open first, leading to a rapid influx of Na+ ions and a positive shift in membrane potential. Following this rapid depolarization, the K+ channels respond to the change in voltage.

These voltage-gated K+ channels do not open immediately; they have a slower activation phase compared to Na+ channels. During repolarization, they open slowly after the peak of the action potential has been reached. The delayed opening allows K+ ions to flow out of the cell, which helps to bring the membrane potential back down toward its resting state.

This characteristic of K+ channels is essential for the proper timing of the action potential. During repolarization, while the Na+ channels are nearing inactivation and beginning to close, the K+ channels are being activated slowly, allowing K+ to exit efficiently and facilitate the restoration of the resting membrane potential.

Thus, the key feature of K+ channels during this phase is their slow opening in response to the depolarization that has just occurred.