Which of the following event occurs during the repolarization phase of an action potential in the neuronal membrane ?

Options

A. K+ inos rapidly move outside the cell
B. Na+ ions rapidly move inside the cell
C. N+ inos rapidly move outside the cell
D. K+ ions rapidly move inside the cell

Answer

To answer the question regarding the event that occurs during the repolarization phase of an action potential in the neuronal membrane, we can break down the process step by step:

### Step-by-Step Solution:

1. **Understanding the Resting State**:
- In the resting state of a neuron, the membrane is polarized. This means that the inside of the neuron is negatively charged compared to the outside. The membrane is permeable to potassium ions (K+) and nearly impermeable to sodium ions (Na+).

2. **Initiation of Action Potential**:
- When a stimulus is applied to the neuron, it causes depolarization. This occurs when sodium channels open, allowing Na+ ions to rush into the cell, making the inside of the neuron more positive.

3. **Transition to Repolarization**:
- After the peak of the action potential, the sodium channels close, and potassium channels open. This transition marks the beginning of the repolarization phase.

4. **Potassium Ion Movement**:
- During the repolarization phase, potassium ions (K+) move out of the neuron. This movement occurs because the permeability of the membrane to K+ increases significantly. As K+ leaves the cell, the inside of the neuron becomes more negative again, restoring the negative charge.

5. **Restoration of Resting Potential**:
- The movement of K+ out of the cell continues until the membrane potential returns to its resting state, completing the repolarization process.

### Conclusion:
The correct event that occurs during the repolarization phase of an action potential in the neuronal membrane is that **potassium ions (K+) move rapidly outside the cell**.