## Core Concept
The question tests knowledge of the cells responsible for myelination in the Peripheral Nervous System (PNS). Myelination is the process by which nerve fibers are covered with a myelin sheath, which facilitates the transmission of electrical impulses along the nerve fiber. In the PNS, this process is crucial for the efficient functioning of the nervous system.

## Why the Correct Answer is Right
The correct answer, **Schwann cells**, are the myelinating cells of the PNS. These cells wrap around the axons of neurons, forming the myelin sheath. This sheath acts as an electrical insulator, speeding up the transmission of signals along the nerve fiber. Schwann cells are derived from the neural crest and play a critical role in the maintenance and regeneration of peripheral nerves.

## Why Each Wrong Option is Incorrect
- **Option A:** Astrocytes are a type of glial cell in the Central Nervous System (CNS) and are not primarily involved in myelination in the PNS. They do play roles in providing nutrients to neurons and in the repair and scarring process of the brain and spinal cord following traumatic injuries.
- **Option B:** Oligodendrocytes are the myelinating cells of the CNS, not the PNS. They can myelinate multiple axons, which is different from Schwann cells that myelinate a single axon.
- **Option D:** Microglia are a type of glial cell located throughout the brain and spinal cord. They act as the first and main form of active immune defense in the CNS but are not involved in myelination.

## Clinical Pearl / High-Yield Fact
A key point to remember is that while Schwann cells myelinate nerve fibers in the PNS, oligodendrocytes are responsible for myelination in the CNS. This distinction is crucial for understanding various neurological diseases and conditions that affect the PNS and CNS differently.

## Correct Answer: C. Schwann cells