The area where medullary sheath is absent in the nerve fibre is

Options

A. Nissal granules
B. Schwann cells
C. Node of Ranvier
D. Schwann node.

Answer

To solve the question, "The area where medullary sheath is absent in the nerve fibre is," we will follow these steps:

### Step-by-Step Solution:

1. **Understand the Medullary Sheath**: The medullary sheath, also known as the myelin sheath, is an insulating layer that surrounds the axons of myelinated nerve fibers. It is composed of myelin, which helps in the effective transmission of electrical impulses along the nerve.

2. **Identify the Options**: The options provided are:
- Nissl granules
- Schwann cells
- Node of Ranvier
- Schwann node

3. **Analyze Each Option**:
- **Nissl Granules**: These are found in the cytoplasm of neurons (cyton) and are involved in protein synthesis. They are not related to the myelin sheath, so this option is incorrect.
- **Schwann Cells**: These are glial cells that form the myelin sheath around the axons. Since they are responsible for creating the myelin sheath, this option is also incorrect.
- **Node of Ranvier**: This is the gap between two adjacent Schwann cells along the axon. At this node, the myelin sheath is absent, making this option a potential correct answer.
- **Schwann Node**: This term does not refer to any recognized structure in nerve fibers and is not relevant, making this option incorrect.

4. **Conclusion**: Based on the analysis, the area where the medullary sheath (myelin sheath) is absent in the nerve fiber is the **Node of Ranvier**.

### Final Answer:
The area where the medullary sheath is absent in the nerve fibre is the **Node of Ranvier**.

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