neurilemma

The neurilemma, also known as the sheath of Schwann, is the cytoplasmic outer layer and membrane of a Schwann cell that surrounds a peripheral nerve axon. It is the part of the Schwann cell that contains the cell body’s nucleus and organelles and contact with the axon.

In the peripheral nervous system, myelinated fibers are wrapped by Schwann cells, which form a multilayered myelin sheath around the axon. The neurilemma lies on the outer surface of this myelin sheath, providing a continuous cytoplasmic border around the axon. For unmyelinated fibers, Schwann cells envelop several small-diameter axons; each axon is surrounded by a portion of Schwann cell cytoplasm with its own neurilemmal boundary.

The neurilemma is derived from neural crest cells and remains a defining feature of peripheral nerves. Its presence includes the Schwann cell nucleus and cytoplasm, which are essential for cellular maintenance and response to injury.

A key function of the neurilemma is its role in peripheral nerve regeneration. Following injury, Schwann cells proliferate and organize into guiding pathways known as bands of Büngner within the neurilemma, supporting axonal regrowth toward targets. This regenerative capability is a characteristic difference from the central nervous system, where axonal regrowth is limited in part due to the absence of a comparable neurilemmal sheath and inhibitory environments.