Myelin in CNS is formed by:
**Core Concept**
The formation of myelin in the central nervous system (CNS) is a complex process involving specialized cells that produce and deposit the myelin sheath around neuronal axons. This process is essential for the proper functioning of the CNS, enabling rapid transmission of electrical signals.
**Why the Correct Answer is Right**
Myelin in the CNS is primarily formed by oligodendrocytes, a type of glial cell. These cells extend their processes to wrap around the axons of multiple neurons, producing a compact myelin sheath that facilitates saltatory conduction. This process is crucial for the efficient transmission of neural signals within the CNS.
**Why Each Wrong Option is Incorrect**
* **Option A:** Schwann cells are responsible for myelination in the peripheral nervous system (PNS), not the CNS. While they share some similarities with oligodendrocytes, their role and function are distinct.
* **Option B:** Astrocytes, another type of glial cell, play a critical role in maintaining the blood-brain barrier, providing support and nutrients to neurons, and regulating the extracellular environment. However, they are not involved in myelin formation.
* **Option D:** Microglia are the resident immune cells of the CNS, responsible for phagocytosing debris and pathogens. They do not contribute to the formation of myelin.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that the myelin sheath is not a static structure; it is dynamic and can be affected by various pathological processes, including demyelinating diseases such as multiple sclerosis.
**Correct Answer:** C. Oligodendrocytes.