A nerve impulse will travel through a nerve fibre only if its membrane suddenly becomes more permeable to ions of

Options

A. Sodium
B. Calcium
C. Chloride
D. Potassium

Answer

### Step-by-Step Solution:

1. **Understanding Nerve Impulse**: A nerve impulse, also known as an action potential, is an electrical signal that travels along a nerve fiber. It is generated when there is a sudden change in the permeability of the nerve fiber's membrane to certain ions.

2. **Role of Ion Channels**: The generation of a nerve impulse involves voltage-gated ion channels, which are primarily responsible for the movement of sodium (Na⁺) and potassium (K⁺) ions across the membrane of the nerve fiber.

3. **Resting Membrane Potential**: In a resting nerve fiber, the inside of the axoplasm (the cytoplasm of the nerve cell) is negatively charged compared to the outside interstitial fluid. This difference in charge is due to the unequal distribution of ions: Na⁺ is more concentrated outside the cell, while K⁺ is more concentrated inside.

4. **Ion Concentration Gradient**: The concentration of Na⁺ ions is approximately 16 times higher outside the axoplasm than inside, while K⁺ ions are about 25 times more concentrated inside than outside. This creates a gradient that drives the movement of these ions.

5. **Action Potential Initiation**: When a stimulus occurs, the nerve membrane becomes more permeable to Na⁺ ions. This increased permeability allows Na⁺ ions to diffuse into the axoplasm, leading to a rapid depolarization of the membrane.

6. **Conclusion**: Therefore, for a nerve impulse to travel through a nerve fiber, the membrane must suddenly become more permeable to sodium ions (Na⁺). Hence, the correct answer is sodium ions.

### Final Answer:
A nerve impulse will travel through a nerve fiber only if its membrane suddenly becomes more permeable to **sodium ions (Na⁺)**.

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