Which of the following increases when an action potential is initiated ?

Options

A. Diffusion of `Na^(+)` ions into the neuron
B. Diffusion of `Na^(+)` ions out of the neuron
C. Diffusion of `K^(+)` ions into the neuron
D. Diffusion of `K^(+)` ions out of the neuron

Answer

To solve the question "Which of the following increases when an action potential is initiated?", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Action Potential**:
- An action potential is a rapid change in the membrane potential of a neuron, which occurs when a stimulus causes the neuron to become depolarized.

2. **Resting State of Neuron**:
- In the resting state, the neuronal membrane is polarized. The inside of the neuron is negatively charged compared to the outside, primarily due to the higher concentration of potassium ions (K+) inside and sodium ions (Na+) outside.

3. **Initiation of Action Potential**:
- When a stimulus is applied, the membrane becomes permeable to sodium ions (Na+). This permeability change allows sodium ions to diffuse into the neuron.

4. **Diffusion of Sodium Ions**:
- As sodium ions diffuse into the neuron, the positive charge from the sodium ions causes the inside of the neuron to become more positive, leading to depolarization.

5. **Conclusion**:
- Therefore, the correct answer to the question is that the **diffusion of sodium into the neuron increases** when an action potential is initiated.

### Final Answer:
The correct option is: **Diffusion of sodium into the neuron.**

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