Regeneration

After a short lag period, regeneration of a peripheral nerve occurs simultaneously with degeneration. The cell body DNA undergoes chromatolysis in preparation for mRNA and protein production. Subsequently, tubulin protein production increases. The proximal end of the nerve proliferates to form a growth cone of multiple axons. These advance in multiple directions through the collagenous scar formed by fibroblasts at the site of injury. Beyond the scar, successful axons dock with endoneurial tubes along the line of previous axons. Around these tubes the Schwann cells are already in position to myelinate the advancing axon. External to the Scwhann cells, a new collagen sleeve contracts with time to narrow the diameter of the nerve fibres.

Regeneration is dependent upon a number of physiological factors:

• soluble growth factors:
  • secreted by a variety of cells eg:
    • postsynaptic neurones
    • muscle cells
    • Schwann cells
  • two types:
    • neurotropic: guide nerve growth
    • neutrotrophic: encourage growth
• surface cues: eg laminins and adhesion molecules secreted by Schwann cells