•Peripheral nerve injuries almost always involve axons only, not the cell bodies. This is what sets spinal cord injuries apart from them. [Module 2(b)]
•After the injury, the part of axon severed from the main cell body starts to disintegrate. This is known as Wallerian degeneration.
•A scientist named Waller discovered this process in 1862.
•Wallerian degeneration does not affect the Schwann cells (the cells providing the myelin sheath) if they are not destroyed by the injury.
•They, along with macrophage cells, clear the debris of degenerating axon
•This leaves an empty tunnel of the Schwann cells as the axon is degenerating.
•Once the damaged axon segment is removed completely, the cell body starts to grow a new axon in the empty tunnel left by Wallerian degeneration.
•This process is known as Wallerian regeneration. The success depends on the remaining Schwann cells, as they help guide the re-growing axon to its correct destination.
•Once the new axon reach the injury site, it tries to reconnect with the axon segment across the injury site. The success depends on the injury.