1. Neuroplasticity and Responses to Nervous System Damage
Degeneration - deterioration
Regeneration – regrowth of damaged neurons
Reorganization
Recovery
Copyright © 2006 by Allyn and Bacon

2. What happens when an axon is severed (cut)?
Both portions of the axon degenerate

3. proximal portion of axon
distal portion of axon

4. Degeneration
Anterograde - degeneration of the axonal segment – between the cut and synaptic terminal
cut off from cell’s metabolic center- axon
swells and breaks off within a few days
Copyright © 2006 by Allyn and Bacon

5. Anterograde degeneration

6. Retrograde degeneration– degeneration of the segment between the cut and cell body
takes place more slowly
if regenerating axon makes a new synaptic contact, the neuron may survive

7. Anterograde degeneration
Retrograde degeneration

8. Neural Regeneration
Regeneration is virtually nonexistent in the CNS of adult mammals and unlikely, but possible, in the PNS
Copyright © 2006 by Allyn and Bacon

9. What happens in the PNS? Only occurs at the proximal end of axon
Axonal sprouting

10. Axonal sprouting

11. at the same time…..
if myelin sheaths line up – they secrete “growth promoting” factors
AND if one of the sprouts matches up – it will begin to grow and reestablish connections

13. Why doesn’t this happen in the CNS?
differences in the glial cells that make myelin
In PNS – Schwann cells make myelin sheaths
In CNS – oligodendroglia make myelin sheaths
HOW THESE GLIAL CELLS DO THIS IS VERY DIFFERENT!!!

14. What are some of these differences?
Schwann cell – each Schwann cell is a single segment of myelin

15. Each of these is a Schwann Cells

16. What are some of these differences?
Schwann cell – each Schwann cell is a single segment of myelin
Oligodendroglia – make multiple sheaths of myelin

18. Why do mammalian PNS neurons regenerate?
So the different ways they contribute myelin may make a difference
Also - Schwann cells promote regeneration
by releasing neurotrophic factors (stimulate growth)
Oligodendroglia - release “growth inhibiting” factors AND making it impossible for the axon to grow
Copyright © 2006 by Allyn and Bacon

19. Reorganization
Can occur in the CNS

20. Adult stem cell neurogenesis
Two regions in the brain that we know this occurs
Part of the hippocampus
Subventricular zone – area of lining of ventricles in brain
Controversy regarding the role of these