Myelin sheath is formed by

Options

A. Ranvier cells
B. muscle cells
C. Schwann cells
D. axon

Explanation

To answer the question "Myelin sheath is formed by," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Myelin Sheath**:
- The myelin sheath is a protective covering that surrounds the axons of myelinated nerve fibers. It plays a crucial role in the efficient transmission of electrical impulses along the nerve cells.

2. **Identifying the Cells Involved**:
- The myelin sheath is formed by specific types of cells. In the peripheral nervous system, these cells are known as Schwann cells.

3. **Function of Schwann Cells**:
- Schwann cells wrap around the axons of neurons, creating layers of myelin. This process is essential for forming the myelin sheath, which insulates the axon and enhances the speed of nerve impulse transmission.

4. **Composition of Myelin**:
- The myelin itself is composed of lipids, proteins, and some water. This composition contributes to its insulating properties.

5. **Conclusion**:
- Therefore, the myelin sheath is formed by Schwann cells.

### Final Answer:
The myelin sheath is formed by **Schwann cells**.

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