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

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

proximal portion of axondistal portion of axon

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 Degeneration

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

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

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

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

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!!! Why doesn’t this happen in the CNS?

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

Each of these is a Schwann Cells

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

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 Why do mammalian PNS neurons regenerate?

Can occur in the CNS Reorganization

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! Role of embryonic stem cells

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 Adult stem cell neurogenesis