**Core Concept**
The central nervous system (CNS) is composed of the brain and spinal cord, which are enveloped by a myelin sheath. This sheath is essential for the proper conduction of nerve impulses, allowing for faster transmission of signals. The myelin sheath is formed by specialized cells that wrap around the axons of neurons.

**Why the Correct Answer is Right**
Oligodendrocytes are the primary myelinating cells in the CNS. These cells extend their processes to wrap around the axons of multiple neurons, forming a compact myelin sheath. This process is called myelination, and it allows for the rapid transmission of electrical signals along the length of the neuron. Oligodendrocytes are capable of myelinating multiple axons, which is not characteristic of Schwann cells in the peripheral nervous system. This allows the CNS to achieve faster and more efficient communication between neurons.

**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, they are distinct cells with different functions.
**Option B:** Microglia are a type of glial cell that plays a role in the immune response and phagocytosis of debris in the CNS. They are not involved in the formation of the myelin sheath.
**Option D:** Protoplasmic astrocytes are a subtype of astrocytes that provide support and maintenance functions to neurons in the CNS. While they are important for the overall health of the nervous system, they are not responsible for myelination.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that oligodendrocytes can myelinate multiple axons, whereas Schwann cells in the PNS myelinate a single axon. This distinction is critical for diagnosing demyelinating diseases such as multiple sclerosis, which primarily affects the CNS.

**✓ Correct Answer: C. Oligodendrocytes**