**Question:** Myelin sheath in CNS is produced by

A. Schwann cells
B. Astrocytes
C. Oligodendrocytes
D. Ependymal cells

**Core Concept:** The myelin sheath is a fatty insulating layer that surrounds axons of neurons in the central nervous system (CNS), reducing the electrical resistance and speeding up the transmission of nerve impulses. This process is known as myelination and is crucial for efficient neuronal communication.

**Why the Correct Answer is Right:** In the CNS, the myelin sheath is produced by a specific type of glial cell called oligodendrocytes. These cells are responsible for generating the myelin sheath that envelops axons, thereby enhancing their conductivity.

**Why Each Wrong Option is Incorrect:**

A. Schwann cells are primarily involved in myelination within the peripheral nervous system (PNS), not the CNS.
B. Astrocytes are glial cells that support and maintain the CNS environment, but they do not produce myelin sheaths.
C. Oligodendrocytes are the correct answer, and this option clarifies the correct cell type responsible for myelination in the CNS.
D. Ependymal cells are another type of glial cells, but they form the ependymal layer covering the ventricles and not the myelin sheaths.

**Clinical Pearl:** Understanding the role of oligodendrocytes in myelination is essential for grasping the fundamental principles of nervous system functioning.

**Correct Answer:** C. Oligodendrocytes produce the myelin sheath in the CNS.