Myelin sheath in CNS is synthesized by :
**Core Concept**
The myelin sheath in the central nervous system (CNS) is a complex structure composed of lipids and proteins that surrounds and insulates axons, facilitating faster transmission of electrical signals. Myelination is a crucial process for the proper functioning of the CNS.
**Why the Correct Answer is Right**
The myelin sheath in the CNS is synthesized by oligodendrocytes. These specialized glial cells extend their processes to wrap around the axons of multiple neurons, forming the myelin sheath. This process involves the expression of specific genes and proteins, including myelin basic protein (MBP) and proteolipid protein (PLP), which are essential for the formation and maintenance of the myelin sheath. Oligodendrocytes are responsible for myelinating a single axon multiple times, increasing the speed of signal transmission.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect, as oligodendrocytes are the primary cells responsible for myelination in the CNS, not astrocytes.
**Option B:** Incorrect, as Schwann cells are responsible for myelination in the peripheral nervous system (PNS), not the CNS.
**Option C:** Incorrect, as microglia are a type of glial cell involved in immune function and phagocytosis, not myelination.
**Clinical Pearl / High-Yield Fact**
Oligodendrocytes can myelinate multiple axons, increasing the speed of signal transmission and making the CNS more efficient. This process is essential for the proper functioning of the CNS, and disruptions in myelination can lead to neurological disorders such as multiple sclerosis.
**Correct Answer: D. Oligodendrocytes**