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EPSP's, IPSP's, and spikes.

Neuromancer glenne at csd4.csd.uwm.edu
Mon Sep 27 14:47:07 EST 1993


Hi,
 
Perhaps you remember the article posted on this newsgroup regarding
the use of tree grammars to model membrane potentials.  I showed the
article to my formal languages/grammars/automata class professor, and
he'd like me to discuss it with the class.
 
I have gotten a rough idea of what tree grammars are and would like to
get some confirmation and correction of my views of membrane potentials.
I am a computer scientist at this point, and have picked up a very limited
amount of neurobiology by reading neuroscience books for entertainment.
I wish to clear up some of my "knowledge" before I email questions to the
person who posted the article.
 
Most of this is pure guesswork.  I am assuming that there is such a
thing as a dendritic bouton.  Suppose we are at the dendritic bouton. Some
neurotransmitters are released onto this bouton causing an EPSP.  All
EPSP's and IPSP's die out due to the same reason that we have a resting
potential.  (The membrane at this bouton allows some of the positive ion's
out while not allowing other positive ions in.)  I would guess that some
of the voltage of these EPSP's will overflow onto other nearby boutons and
would still be considered EPSP's as long as they died out.
 
However, suppose some more neurotransmitters are released on this bouton.
only this time, many EPSP's are occuring on all kinds of nearby
dendritic boutons.  In fact there are so many EPSP's occuring that the
potential cannot be drained away through this bouton's membrane, nor the
nearby membranes, but instead the voltage flows all the way to the soma
and down the axon where the electrical potential is converted the chemical
ejection of neurotransmitters.  I.E. after a threshold amount of EPSP's
occur an action potential occurs.  (Is an action potential synonymous
with a spike?)
 
However while this would seem to be a reasonable explanation of how
ESPS's get translated into an action potential, it might be even more
efficient if somehow, once an action potential had built up,
this would change the neural membrane so that the action potential could
not leak out at all through the membrane as it traveled to the soma and
the axon.
 
Anyone care to shed any light on this wild speculation?
 
Thanks in advance,
 
Glenn           glenne at csd4.csd.uwm.edu



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