Schwann cells are glia cells which surround the axons of the peripheral nervous system and can be subcategorized to myelinating and non-myelinating cells. Myelinating Schwann cell wrap around a single axonal segment, with a diameter exceeding 1µm to form the myelin sheath. This multilayered spiral sheath, is predominantly lipids, but contains several proteins that take on key roles in maintaining the structure and compaction of the myelin and adhesion of the sheath to the axon. During salutary conduction, the electrically insulating sheath, allow for action potential jumps from one node of Ranvier to another, which are the gaps between adjacent Schwann cells.
Schwann cells are the peripheral nervous system's analogues of the central nervous system's oligodendrocytes. However, one Schwann cell myelinates one axonal segment, whereas each oligodendrocyte typically myelinates many axons.
In response to peripheral nerve injury, myelinating Schwann cells dedifferentiate into repair cells that are essential for axonal regeneration, and then redifferentiate into myelinating Schwann cells to restore nerve function.
Non-myelinating Schwann cells surround several small diameter axons, ensheathing each axon in a pocket of Schwann cell cytoplasm, forming a Remak bundle. These cells are important for providing support and nutrition to the axon, ensuring their survival.
Schwann cell development begins with differentiation of the neural crest cells into Schwann precursor cells, which then mature to form immature Schwann cells. At birth, Schwann cells progressively sort axons from the main bundle, through the process called radial sorting; Schwann cells which associate with a single larger in diameter axonal segment will become myelinating Schwann cells. In contrast, immature Schwann cells which associate with several small caliber axons will become non-myelinating Schwann cells.