Which of the following option would not associated with a decrease in conduction velocity of a nerve impulse in a neuron :-

Options

A. Increasing the length of the axon
B. Removing the myelin sheath
C. Cooling the axon
D. Increasing pressure on axon

Answer

To determine which option would not be associated with a decrease in conduction velocity of a nerve impulse in a neuron, we need to analyze the options given and their effects on conduction velocity.

### Step-by-Step Solution:

1. **Understanding Conduction Velocity**:
- Conduction velocity refers to the speed at which an electrical impulse travels along a neuron. It is influenced by several factors, including the presence of myelin, temperature, and the physical properties of the axon.

2. **Evaluating the Options**:
- **Option 1: Increasing the length of the axon**:
- The length of the axon does not significantly affect conduction velocity, especially if the axon is myelinated. Myelination allows for faster conduction through saltatory conduction, where the impulse jumps between nodes of Ranvier. Thus, increasing the length of the axon would not necessarily decrease conduction velocity.

- **Option 2: Removing the myelin sheath**:
- Myelin sheaths are crucial for increasing conduction velocity. Removing them would lead to a significant decrease in conduction speed as the impulse would have to travel continuously along the axon rather than jumping. Therefore, this option is associated with a decrease in conduction velocity.

- **Option 3: Cooling the axon**:
- Lower temperatures can slow down the conduction velocity as they affect the ion channels and the overall metabolic activity of the neuron. Thus, cooling the axon would decrease conduction velocity.

- **Option 4: Increasing the pressure on the axon**:
- Increasing pressure on the axon could potentially compress it and affect the conduction negatively, leading to a decrease in conduction velocity. However, this option is less straightforward compared to the others.

3. **Conclusion**:
- Based on the analysis, the option that would not be associated with a decrease in conduction velocity of a nerve impulse in a neuron is **Option 1: Increasing the length of the axon**.

### Final Answer:
**Option 1: Increasing the length of the axon.**