The myelin sheath in the CNS is formed by which type of cells?

• A. Schwann cells
• B. Oligodendrocytes
• C. Astrocytes
• D. Microglia

Answer: (B)

The myelin sheath in the central nervous system (CNS) is indeed formed by oligodendrocytes. These specialized glial cells are responsible for myelinating multiple axons in the CNS, which helps to electrically insulate the axons and enhance the speed of action potentials through a process called saltatory conduction. Myelination is crucial for the proper functioning of the nervous system, as it allows for rapid transmission of nerve impulses along the axons.

Oligodendrocytes can wrap around multiple axons simultaneously, creating segments of myelin sheath between nodes of Ranvier, which are small gaps that facilitate rapid signal propagation. This structural adaptation is essential in ensuring efficient communication between neurons in the CNS.

In contrast, other cell types mentioned, such as Schwann cells, form the myelin sheath in the peripheral nervous system, while astrocytes play a supportive role in maintaining the environment around neurons and working with the blood-brain barrier. Microglia are immune cells in the CNS that provide defense against pathogens and remove debris. Therefore, oligodendrocytes are the specific cells that create the myelin sheath within the central nervous system.