gliaSchwann

Schwann cells are a type of glial cell belonging to the peripheral nervous system. They are responsible for forming the myelin sheath around axons of neurons in the PNS. Myelin is a fatty insulating layer that significantly speeds up the transmission of electrical impulses along the axon. This process is crucial for efficient nerve function. Each Schwann cell myelinates a single segment of an axon. In unmyelinated axons, Schwann cells still play a supportive role by wrapping around multiple axons, providing metabolic support and protection.

The formation of the myelin sheath by Schwann cells is a complex process involving the wrapping of the cell membrane around the axon multiple times. The nucleus and cytoplasm of the Schwann cell are pushed to the outer layers, forming the outermost layer called the neurilemma. The myelin sheath is not continuous along the axon; there are small gaps called nodes of Ranvier where the axon is exposed. These nodes are important for saltatory conduction, a process where the electrical impulse jumps from one node to the next, greatly increasing the speed of transmission.

Schwann cells also play a vital role in nerve regeneration in the PNS. If a peripheral nerve axon is damaged, Schwann cells can dedifferentiate and proliferate, forming a cellular cord that guides regenerating axons. They also clear debris from the injury site and provide trophic factors that support axon regrowth. This regenerative capacity is generally more robust in the PNS compared to the central nervous system. Schwann cells are essential for maintaining the health, function, and repair of peripheral nerves.