Neuroplasticity and Responses to Nervous System Damage Degeneration - deterioration Regeneration – regrowth of damaged neurons Reorganization Recovery Copyright © 2006 by Allyn and Bacon
What happens when an axon is severed (cut)? Both portions of the axon degenerate
proximal portion of axon distal portion of axon
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
Anterograde degeneration
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
Anterograde degeneration Retrograde degeneration
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
What happens in the PNS? Only occurs at the proximal end of axon Axonal sprouting
Axonal sprouting
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
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!!!
What are some of these differences? Schwann cell – each Schwann cell is a single segment of myelin
Each of these is a Schwann Cells
What are some of these differences? Schwann cell – each Schwann cell is a single segment of myelin Oligodendroglia – make multiple sheaths of myelin
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
Reorganization Can occur in the CNS
Role of embryonic stem cells what are stem cells? derived from embryos most are derived from embryos that develop from eggs that have been fertilized in vitro (IVF) — in an in vitro fertilization clinic—and then donated for research purposes with informed consent of the donors. They are not derived from eggs fertilized in a woman's body. pluripotent- can develop into many cell types!
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