10.10

• Why do mammalian PNS neurons regenerate but mammalian CNS neurons normally do not?

  Something about the environment of the PNS promotes regeneration and something about the environment of the CNS does not. Schwann cells seem to be one factor.
• Schwann cells, which myelinate PNS axons, clear the debris and scar tissue resulting from degeneration, proliferate to produce more Schwann cells, and promote regeneration in the mammalian PNS both by producing neurotrophic factors and by forming physical tracks to guide the regrowth of axons.
• Oligodendroglia, which myelinate CNS axons, do not clear debris or stimulate or guide regeneration; indeed, they release factors that actively block regeneration
• In the CNS, astrocytes form a glial scar after injury that presents a physical barrier to axonal regrowth and also actively releases inhibitors of axonal growth.
• When an axon degenerates, axon branches grow out from adjacent healthy axons and synapse at the sites vacated by the degenerating axon; this is called collateral sprouting.
• brain swelling


  cerebral edema
• Cognitive reserve (roughly equivalent to education and intelligence) is thought to play a role in the improvements observed after brain damage that do not result from true recovery of brain function.
• Neurotransplantation as a Treatment for CNS Damage: Early Research

  1. implanting embryonic tissue near the damaged area
  2. adrenal medulla autotransplantation
  3. implanted nonneural cells
  4. implanting Schwann cell sheathes
• transplanting a patient’s own adrenal medulla cells into their striatum, usually for the treatment of Parkinson’s disease.

  adrenal medulla autotransplantation
• The constraint-induced therapy inspired by the principle, that neurons seem to be in a competitive situation: They compete with other neurons for synaptic sites and neurotrophins, and the losers die.

  constraint-induced therapy
• Enriched environments are those designed to promote cognitive and physical activity—they typically involve group housing, toys, activity wheels, and changing stimulation.
• Most amputees continue to experience the limbs that have been amputated—a condition referred to as phantom limb.