Biological Systems MCAT Practice Exam 2025 - Free Biological Systems Practice Questions and Study Guide

The repolarization of a neuron is primarily facilitated through the opening of potassium (K+) channels. During an action potential, after the depolarization phase occurs (when sodium (Na+) channels open and allow Na+ ions to rush into the cell), the neuron reaches a peak membrane potential. To restore the membrane to its resting state, K+ channels open, allowing K+ ions to flow out of the neuron. This outflow of positively charged K+ ions helps to bring the membrane potential back down, effectively repolarizing the neuron.

The role of K+ channels is crucial as it directly counteracts the previous influx of Na+ ions that contributed to depolarization. This process is a key component of the action potential and is essential for the proper functioning of neurons, allowing them to return to their resting state in preparation for another action potential.

In contrast, Na+ channels are primarily responsible for depolarization, while calcium (Ca2+) channels are involved in the initiation of neurotransmitter release at synapse but do not contribute directly to repolarization. Chloride (Cl-) channels can play a role in stabilizing the membrane potential but they are not the primary channels responsible for the repolarization process during an action potential. Thus