Neurilemma

The outermost layer of the nerve fiber in the peripheral nervous system

Neurilemma

The neurilemma, also known as the sheath of Schwann, is the outermost layer of the myelinated or unmyelinated nerve fibers in the peripheral nervous system (PNS). It is formed by Schwann cells, which are a type of glial cell that play a crucial role in the maintenance and regeneration of peripheral nerves.

Structure

The neurilemma is a thin, delicate membrane that envelops the axon of a nerve cell. In myelinated nerve fibers, the neurilemma is the outermost layer of the myelin sheath, which is composed of multiple layers of Schwann cell membrane wrapped around the axon. In unmyelinated fibers, the neurilemma still surrounds the axon, but without the multiple layers of myelin.

File:Neuron with Schwann cell.png

Diagram of a neuron with a Schwann cell forming the myelin sheath and neurilemma.

Function

The primary function of the neurilemma is to protect and insulate nerve fibers, facilitating the rapid transmission of nerve impulses along the axon. Additionally, the neurilemma plays a vital role in the regeneration of damaged nerve fibers. When a peripheral nerve is injured, the neurilemma provides a pathway for the regrowth of the axon, allowing for the potential recovery of nerve function.

Regeneration

Unlike the central nervous system (CNS), where nerve regeneration is limited, the PNS has a greater capacity for repair and regeneration, largely due to the presence of the neurilemma. Schwann cells within the neurilemma secrete growth factors and form a regeneration tube that guides the regrowing axon to its target.

Clinical Significance

Damage to the neurilemma can result in impaired nerve function and delayed or incomplete nerve regeneration. Conditions such as neuropathy and nerve compression syndromes can affect the integrity of the neurilemma, leading to symptoms such as pain, numbness, and muscle weakness.

Related pages

• Schwann cell
• Myelin sheath
• Peripheral nervous system
• Nerve regeneration
• Glial cell