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Regeneration of nerves.

Richard S. Norman rnorman at umich.edu
Sun Oct 20 09:28:25 EST 2002

On Sun, 20 Oct 2002 00:52:02 GMT, "Bill Browning"
<bbrownin at nospamverizon.net> wrote:

>Regeneration of nerves.
>     When a severed hand is reattached, how is the nerve restored?  Do new
>nerve bodies form and grow new axons?  Do the old axons rejoin their
> segments?  Do the proximal parts of the old axons extend along the
> route of the nerve?  How do the new nerves find the right places?
> Does the sensation starting at the thumb give a sensation associated
> with the thumb or is it random and the patient learns how it works?
>Bill B.

When a peripheral nerve is severed, the axons degenerate back to the
cell bodies in the spinal cord (or the dorsal root ganglia, for
sensory cells).  Then the axons regrow back along the old pathways. If
the cut ends of the nerve are sutured together or are joined in some
other way, then it is possible for at least some of the growing axons
to find their way back to their original targets. The cells "know"
(through chemical signals) just where they "belong" and preferentially
reform the same functional connections they had originally, if
possible.  However, the axons can innervate the wrong muscles or "get
lost" along the way.  

If the original contact is re-established, then the function is simply
restored.  Otherwise, either you relearn or else the function remains
lost.  It is very variable -- sometimes a surprising amount of
function is regained, sometimes a dissappointing amount is lost.

See "peripheral nerve  regeneration" on www.google.com, for example.

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