Myelin sheath is produced by
or
Myelin of the nerve fibres of the central nervous system is produced and maintained by

Options

A. Schwann cells and Oligodendrocytes
B. Astrocytes and Schwann cells
C. Oligodendrocytes and Osteoclasts
D. Osteoclasts and Astrocytes

Answer

### Step-by-Step Solution

1. **Understanding Myelin Sheath**:
- The myelin sheath is a protective covering that surrounds the axons of neurons. It is primarily composed of a phospholipid membrane, which provides insulation to the axon.

2. **Function of Myelin Sheath**:
- The main function of the myelin sheath is to act as an insulating layer, which helps maintain a constant membrane potential in the axon. This insulation is crucial for the efficient transmission of electrical signals along the nerve fibers.

3. **Cells Responsible for Myelin Production**:
- Myelin sheath is produced by specific types of cells. In the peripheral nervous system (PNS), myelin is produced by Schwann cells. In contrast, in the central nervous system (CNS), myelin is produced by oligodendrocytes.

4. **Identifying the Correct Answer**:
- The question asks who produces and maintains the myelin of nerve fibers in the central nervous system. Since oligodendrocytes are responsible for this function in the CNS, and Schwann cells are responsible in the PNS, the correct answer to the question is that myelin is produced by Schwann cells and oligodendrocytes.

5. **Evaluating the Options**:
- The options provided in the question are:
- a) Schwann cell and oligodendrocyte
- b) Astrocytes and Schwann cells
- c) Oligodendrocyte and osteoclast
- d) Osteoclast and astrocytes
- The first option (Schwann cell and oligodendrocyte) is the only correct answer as it directly addresses the production of myelin in both the PNS and CNS.

### Final Answer
- The correct answer is: **Schwann cells and oligodendrocytes (Option a)**.

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