Peripheral Nerve Injury - Overview of Events in Peripheral Regeneration

Overview of Events in Peripheral Regeneration

Wallerian degeneration is a process that occurs before nerve regeneration and can be described as a cleaning or clearing process that essentially prepares the distal stump for reinnervation. Schwann cells are glial cells in the peripheral nervous system that support neurons by forming myelin that encases nerves. During Wallerian degeneration Schwann cells and macrophages interact to remove debris, specifically myelin and the damaged axon, from the distal injury site. (medscape) Calcium has a role in the degeneration of the damage axon. Bands of Büngner are formed when un-innervated Schwann cells proliferate and the remaining connective tissue basement membrane forms endoneurial tubes. Bands of Büngner are important for guiding the regrowing axon.

At the neuronal cell body, a process called chromatolysis occurs in which the nucleus migrates to the periphery of the cell body and the endoplasmic reticulum breaks up and disperses. Nerve damage causes the metabolic function of the cell to change from that of producing molecules for synaptic transmission to that of producing molecules for growth and repair. These factors include GAP-43, tubulin and actin. Chromatolysis is reversed when the cell is prepared for axon regeneration.

Axon regeneration is characterized by the formation of a growth cone. The growth cone has the ability to produce a protease that digests any material or debris that remains in is path of regeneration toward the distal site. The growth cone responds to molecules produced by Schwann cells such as laminin and fibronectin.