Depolarisation of axolemma during nerve conduction takes place because

Options

A. equal amount of `Na^+ and K^+` move out across axolemma
B. only `Na^+` move inside
C. more `Na^+` moves outside than `K^+` moving outside
D. None of these

Explanation

### Step-by-Step Solution:

1. **Understanding Resting Potential**:
- The axolemma (the membrane of the axon) is initially at a resting potential, which means it is polarized. This polarization is due to the difference in ion concentrations inside and outside the neuron, primarily sodium (Na⁺) and potassium (K⁺) ions.

2. **Nerve Impulse Activation**:
- When a nerve impulse reaches the axolemma, it triggers a change in the membrane potential. This is the starting point for depolarization.

3. **Opening of Sodium Channels**:
- The nerve impulse causes the voltage-gated sodium channels in the axolemma to open. This is a critical step in the process of depolarization.

4. **Influx of Sodium Ions**:
- Once the sodium channels open, Na⁺ ions rush into the neuron due to both the concentration gradient (higher concentration outside) and the electrical gradient (the inside of the cell is negatively charged relative to the outside).

5. **Change in Membrane Potential**:
- The influx of Na⁺ ions causes the inside of the axolemma to become less negative (or more positive), leading to depolarization. This change in charge across the membrane is what constitutes the depolarization phase of the action potential.

6. **Conclusion**:
- Therefore, depolarization of the axolemma during nerve conduction occurs primarily because sodium ions (Na⁺) move into the neuron, making the inside of the axolemma more positive.

### Final Answer:
Depolarization of the axolemma during nerve conduction takes place because sodium ions (Na⁺) move into the neuron.

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