**Core Concept**
Myelin sheath is a critical component of the central nervous system (CNS) and peripheral nervous system (PNS), serving as an insulating layer around axons to facilitate rapid transmission of electrical signals. The synthesis of myelin sheath involves the coordinated effort of oligodendrocytes in the CNS and Schwann cells in the PNS.

**Why the Correct Answer is Right**
In the CNS, oligodendrocytes extend their processes to multiple axons, producing and wrapping myelin around them. This process is essential for the development and maintenance of myelinated nerve fibers. The myelination process involves the interaction between oligodendrocytes and the axonal membrane, leading to the formation of compact myelin. The enzymes involved in myelin synthesis include galactocerebroside synthase, which catalyzes the formation of galactocerebroside, a key component of myelin.

**Why Each Wrong Option is Incorrect**
* **Option A:** is incorrect because it does not accurately represent the cell type responsible for myelin synthesis in the CNS.
* **Option B:** is incorrect because it is a type of glial cell found in the CNS, but it is not directly involved in myelin synthesis.
* **Option C:** is incorrect because it is a type of glial cell found in the PNS, responsible for myelin synthesis, but the question is asking about the CNS.

**Clinical Pearl / High-Yield Fact**
Oligodendrocytes are responsible for the myelination of approximately 1,000,000 axons in the adult human CNS.

**Correct Answer:**. **Oligodendrocytes.**