A Schwann cell provides myelin around axons in the peripheral nervous system.
Schwann cells are glial cells found outside the brain and spinal cord. A myelinating Schwann cell wraps its membrane repeatedly around one segment of a peripheral axon, forming a myelin sheath that electrically insulates the fibre and speeds saltatory conduction between nodes of Ranvier.
One Schwann cell typically myelinates one internodal segment of one axon. Schwann cells can also support non-myelinated axons by surrounding them without forming a thick myelin sheath. They contribute to repair after some peripheral-nerve injuries, although recovery depends on the severity and location of damage.
The most important comparison is with oligodendrocytes. Oligodendrocytes make myelin in the central nervous system and can extend processes to segments of multiple axons. Astrocytes support and regulate neural tissue, while microglia provide immune surveillance; neither is the usual answer for peripheral myelin.