Which glial cell in the peripheral nervous system forms the myelin sheath around peripheral neurons?

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

Answer: (B)

In the peripheral nervous system, insulation of axons to speed signals is provided by glial cells called Schwann cells. They wrap around a segment of the axon and lay down myelin, forming a myelin sheath that speeds conduction via saltatory conduction. Each Schwann cell myelinates a portion of a single axon, with gaps between segments known as nodes of Ranvier where the nerve impulse can jump along the fiber. Other glial cells have different roles or locations: astrocytes support neurons and the blood-brain barrier, oligodendrocytes myelinate axons in the central nervous system, and microglia act as immune cells in the CNS. Therefore, the glial cell that forms the myelin sheath around peripheral neurons is the Schwann cell.