The axon is damaged but the perineurium and epineurium remain intact.

Leads to central chromatolysis

• Definition: the reaction of a neuronal cell body in response to an axonal injury
• Function: increase in protein synthesis to help restore the integrity of the damaged axon
• Characteristics
  • Swelling of the neuronal body
  • Dispersion of the Nissl bodies (which gives the name chromatolysis (chroma: color; lysis: disintegration))
    • The rough endoplasmatic reticulum of neurons.
  • Displacement of the nucleus to the periphery

Results in Wallerian degeneration

• Definition: an active neuronal degeneration process in response to axonal injury
• Function
  • To clear axonal debris and prevent scarring
  • Facilitate targeted reinnervation and functional recovery of tissues previously innervated by that axon before injury
• Characteristics
  • Initially retained electrical excitability of axonal membrane distal to the injury, lasting up to 36 hours
  • Progressive degeneration of distal segment cytoskeleton with dissolution of axonal membrane
  • Degradation of residual myelin sheath by macrophages and Schwann cells
    • In the central nervous system, phagocytic macrophages/microglia are recruited more slowly because of the blood-brain barrier. This slows removal of the myelin debris, which can persist for years in the degenerating tracts and suppress axonal growth via myelin-associated inhibitory factors.
  • The proximal stump either stays in place or retracts slightly
  • Ultimately, the cell body will sprout regenerative nerve fibers that, ideally, reinnervate the distal tissues.
  • Regeneration is significantly more efficient in the peripheral nervous system than in the central nervous system.
  • Good chance of at least partial recovery