Which of the following best characterizes depolarization, the first phase of the action potential in a neuron?

• A. Efflux of K\(^+\) ions out of the cell, making the membrane potential more negative
• B. Opening of voltage-gated Ca\(^{2+}\) channels, leading to neurotransmitter release
• C. Rapid influx of Na\(^+\) ions into the cell, making the membrane potential more positive
• D. Restoration of the resting membrane potential by the Na\(^+\)/K\(^+\) pump

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the concept of depolarization. Depolarization is the first phase of an action potential in a neuron, during which the membrane potential becomes less negative (more positive) compared to the resting potential.
2. Step 2: Recall the role of ion channels in depolarization. During this phase, voltage-gated Na\(^+\) (sodium) channels open in response to a stimulus, allowing Na\(^+\) ions to flow into the neuron.
3. Step 3: Analyze the effect of Na\(^+\) influx. The rapid influx of positively charged Na\(^+\) ions into the cell causes the inside of the neuron to become more positive relative to the outside, leading to depolarization.
4. Step 4: Eliminate incorrect options. Efflux of K\(^+\) ions out of the cell makes the membrane potential more negative, which is characteristic of repolarization, not depolarization. Opening of voltage-gated Ca\(^{2+}\) channels is associated with neurotransmitter release, not depolarization. The Na\(^+\)/K\(^+\) pump restores the resting membrane potential after the action potential, not during depolarization.
5. Step 5: Identify the correct characterization. The correct description of depolarization is the rapid influx of Na\(^+\) ions into the cell, making the membrane potential more positive.