Nerve impulses are initiated by nerve fibers only when the membrane shall become more permeable to :

Options

A. Adrenaline
B. Phosphorus
C. Sodium ions
D. Potassium ions

Answer

**Step-by-Step Solution:**

1. **Understanding Nerve Impulses**: Nerve impulses are electrical signals that travel along neurons. They are essential for communication within the nervous system.

2. **Role of Membrane Permeability**: The initiation of a nerve impulse depends on the permeability of the neuron's membrane to certain ions. This permeability changes during the process of generating an action potential.

3. **Resting State of the Neuron**: In the resting state, the neuron's membrane is polarized. This means that the inside of the neuron is negatively charged compared to the outside. At this stage, the membrane is impermeable to sodium ions (Na⁺) and permeable to potassium ions (K⁺).

4. **Application of Stimulus**: When a stimulus is applied to the neuron, it causes a change in the permeability of the membrane. Specifically, the membrane becomes more permeable to sodium ions.

5. **Depolarization**: As sodium ions rush into the neuron due to the increased permeability, the interior of the neuron becomes positively charged compared to the outside. This reversal of charge is known as depolarization.

6. **Action Potential**: The change in charge across the membrane creates an electrical potential difference, referred to as action potential. This is the actual nerve impulse that travels along the neuron.

7. **Conclusion**: Therefore, nerve impulses are initiated when the membrane becomes more permeable to sodium ions (Na⁺).

**Final Answer**: Sodium Ion (Na⁺)

---