Chapter

Nerve Regeneration

Thomas M. Brushart

in Nerve Repair

Published on behalf of Oxford University Press

Published in print May 2011 | ISBN: 9780195169904
Published online September 2012 | e-ISBN: 9780199965168 | DOI: http://dx.doi.org/10.1093/med/9780195169904.003.0009
Nerve Regeneration

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  • Sensory and Motor Systems
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Neurons respond to injury by downregulating the factors needed for axonal maintenance and transmission and by upregulating a host of growth-related molecules. Recent work has shown that neuronal growth state is enhanced in young animals and after a previous "conditioniong" injury. Enhanced growth state is signaled through an increase in the intracellular concentration of the second messenger cAMP and is mediated through several downstream pathways. The growth cone is the complex structure at the tip of the regenerating axon that guides its advance in response to contact and diffusible factors in the environment. The organizational unit of the distal stump is the Schwann cell tube, the cylindrical basal lamina made by Schwann cells that previously served a single myelinated axon. The speed and accuracy of regeneration are optimized when the basal lamina remains intact, and are both degraded when the basal lamina has been interrupted. Distal stump Schwann cells that have been denervated by axotomy downregulate genes involved in myelin maintenance and upregulate those needed for Wallerian degeneration, the process of clearing axoplasm and myelin from the Schwann cell tube. These Schwann cells also proliferate and express many growth factors that are likely to contribute to axon regeneration. As regeneration proceeds and they are again contacted by axons they revert to the myelinating phenotype. If denervation is prolonged, they gradually lose their ability to respond to axonal contact so that regeneration is progressively impaired.

Chapter.  63873 words.  Illustrated.

Subjects: Sensory and Motor Systems ; Rehabilitation Medicine

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