13.5 Regeneration of Nervous Tissue

• Regeneration of nervous tissue refers to repair of complete neurons, neuroglia, axons, myelin, synapses. Regeneration in CNS differs from that in PNS in mechanism, speed and amount of regeneration. 
• After injury, nissl bodies within cell body disappear and nucleus moves peripherally within cell body
• After injury, nissl bodies within cell body disappear and nucleus moves peripherally within cell body. If neuron regains function, soma will return to normal location
• After injury, nissl bodies within cell body disappear and nucleus moves peripherally within cell body. If neuron regains function, soma will return to normal location. Unless circulation is restored or pressure removed, neuron may not recover
• Key to recovery is events in axon
• In PNS, schwann cells play role in repairing nerves
• For schwann cells... In wallerian degeneration, axon distal to injury site (distal stump) deteriorates THEN…
• For schwann cells... In wallerian degeneration, axon distal to injury site (distal stump) deteriorates THEN… Macrophages migrate in and phagocytize debris
• Schwann cells in injured area do not degenerate 
• Schwann cells divide and form solid cellular cord following path of axon
• Schwann cells release growth factors promoting axonal regrowth
• If axon cut, new axons begun to emerge from proximal stump within hours
• Crushing/tearing, proximal stump of damaged axon died and regresses, new axon delayed
• During recover, axon grows into injury, schwann cells wrap around it
• If axon stops growing, no normal function
• Entire PNS nerve damaged, only some axons successfully reestablish normal synaptic contacts, meaning impaired permanently
• In CNS, limited regeneration, complicated bc…

  • Many more axons are likely to be involved 
  • Astrocytes produce scar tissue that prevent axon growth across damaged area 
  • Astrocytes release chemicals that block regrowth of axons 
• What is Wallerian degeneration, and where does it occur?

  Wallerian degeneration is the process by which a peripheral nerve distal to an injury undergoes deterioration and regeneration.