Neuroplasticity and Responses to Nervous System Damage Degeneration

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