Which glial cell forms myelin in the peripheral nervous system?

• A. Oligodendrocytes
• B. Schwann cells
• C. Astrocytes
• D. Microglia

Answer: (B)

Schwann cells are responsible for forming myelin in the peripheral nervous system. They wrap around peripheral axons, creating the layered myelin sheath that speeds up electrical signaling by saltatory conduction. Each Schwann cell myelinates a single segment of one axon, and along a single axon in the PNS, many Schwann cells line up to cover the length with myelin. In the central nervous system, myelin is formed by oligodendrocytes, which can extend their processes to wrap multiple axons. Astrocytes and microglia have different roles—astrocytes support neurons and maintain the extracellular environment, while microglia act as immune cells. Some peripheral fibers remain unmyelinated and are associated with non-myelinating Schwann cells that provide support without forming a myelin sheath.