basic question

Richard Norman rnorman at umich.edu
Tue Oct 22 19:28:24 EST 1996


>>> What about axon trunks that route together from one area of cortex to the 
>>next?  If a volley of (classically) efferent information left a nucleus down 
>>several axons that surrounded a non-firing axon, could not the Na+ influx and 
>>K+ efflux in the firing cells cause enough local depolarisation to initiate 
>>an axon potential in a previously non-firing cell?  Then the stimulus would 
>>travel ortho- and antidromically, presumably reaching the soma, although it 
>>may not stimulate a second orthodromic ap as the early segment of the soma 
>>could still be refractory.  If this mechanism works it provides a synapse 
>>free mechanism for synaptic interaction (due to myelination it would 
>>presumably be more common in grey tissue, unless the nodes of ranvier line up 

>Further, what about the unmyelinated C-fibers, often running together in one
>Scwanncell- channel?

Unless the extracellular space is SEVEREly restricted by glial cells (as
in the Mauthner cell electrical interaction), there is more than enough
extracellular volume to allow both ion changes and electrical potentials
to dissipate to small enough levels not to have any significant effect
on adjacent neurons.

I remember a paper on bundled groups of small fibers in octopus brain many
years ago and did a calculation on exactly such an interaction, finding it
to be too small to be effective.

Richard Norman
Department of Natural Sciences
University of Michigan - Dearborn
Dearborn MI  USA
rnorman at umich.edu




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