Which of the following event increases when there is depolarisation of a nerve fibre?

Options

A. Diffusion of sodium ions into the neuron
B. Diffusion of sodium ions out of the neuron
C. Diffusion of potassium ion into the neuron
D. Both (a) and (c)

Answer

To solve the question "Which of the following event increases when there is depolarization of a nerve fibre?", we can follow these steps:

### Step 1: Understand the resting potential of a nerve fiber
- A nerve fiber at rest has a membrane potential of approximately -70 mV. This state is known as the resting phase.

### Step 2: Define depolarization
- Depolarization occurs when the membrane potential becomes less negative (more positive) than the resting potential. This is primarily due to the influx of sodium ions (Na+) into the neuron.

### Step 3: Identify the changes during depolarization
- During depolarization, there is an increase in the permeability of the membrane to sodium ions. As sodium channels open, Na+ ions rush into the neuron, causing the inside of the cell to become more positive.

### Step 4: Determine the event that increases during depolarization
- The key event that increases during depolarization is the diffusion of sodium ions into the neuron. This influx of sodium ions leads to a rise in the membrane potential towards a positive value.

### Step 5: Analyze the other options
- The diffusion of sodium ions out of the neuron occurs during repolarization, not depolarization.
- The diffusion of potassium ions into the neuron also occurs during repolarization, as potassium ions (K+) move out of the neuron to help restore the resting potential.

### Conclusion
- Therefore, the correct answer is that the event that increases during depolarization of a nerve fiber is the **diffusion of sodium ions into the neuron**.