Which of the following statement is true regarding the role acetylcholine in nerve physiology?

Options

A. It increases the selective permeability of the cell membrane
B. It increase the potassium concentration inside the axon
C. It reduces activity of Na-K pump
D. It increase the sodium concentration outside the axon

Answer

To solve the question regarding the role of acetylcholine in nerve physiology, we will analyze each of the provided statements one by one.

### Step-by-Step Solution:

1. **Understanding Acetylcholine**:
- Acetylcholine (ACh) is a neurotransmitter that plays a crucial role in transmitting signals between nerve cells (neurons) and muscle cells.

2. **Evaluating the First Statement**:
- The first statement claims that acetylcholine increases the selective permeability of the cell membrane.
- This statement is **true** because acetylcholine binds to receptors on the postsynaptic membrane, leading to the opening of ion channels. This increases the permeability of the membrane to ions, particularly sodium (Na+), which is essential for depolarization and signal transmission.

3. **Evaluating the Second Statement**:
- The second statement suggests that acetylcholine increases the potassium concentration inside the axon.
- This statement is **false**. Acetylcholine does not increase potassium concentration; instead, it primarily affects sodium and calcium ions.

4. **Evaluating the Third Statement**:
- The third statement claims that acetylcholine reduces the activity of the potassium and sodium pump.
- This statement is also **false**. Acetylcholine does not directly reduce the activity of these pumps; rather, it influences ion flow across the membrane through receptor activation.

5. **Evaluating the Fourth Statement**:
- The fourth statement states that acetylcholine increases the sodium concentration outside the axon.
- This statement is **false**. Acetylcholine primarily facilitates the influx of sodium ions into the neuron, which increases the sodium concentration inside the cell, not outside.

### Conclusion:
After evaluating all the statements, the only true statement regarding the role of acetylcholine in nerve physiology is that it increases the selective permeability of the cell membrane.