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[Neuroscience] Re: Electrical Synapses..

jason jkrah_dot_geo_ at yahoo_dot.com
Tue Feb 21 22:19:54 EST 2006

Hi 'r norman'
thank you so very much for your detailed reply.. I did not know if this 
was a silly question - but I could not find much on axo-axonal elect' 
synapses anywhere on google..

I get the impression that importance of elect' synapses have sort of 
underestimated over the years... Most introductory reading I have found 
always goees with great detail about the chem synaps and only brush over 
elect syapses..

r norman wrote:
> On Mon, 13 Feb 2006 10:14:22 +1100, "freenews.iinet.net.au"
> <jkrah_dot_geo_ at yahoo_dot.com> wrote:
>>I hope this is an ok place to ask this questions (begginer) .. I am 
>>studying basic neurobiology and am wondering about axo-axonal electrical 
>>Is it a safe to assume that the synapse must be close enough to the Axon 
>>Hilckock (or AP generating zone) for an Actionm Potential to be 
>>generatable.. of can (axo-axonal) electrical synapses have effect 
>>anywhare along an axon ??
>>Appols - if this is not the appropriate group  :-(
> I know this is very long delayed, but I am on vacation and have not
> had a chance to scan the news group before now.
> Why are you asking about this very special type of synapse, if it even
> exists?  It is a very specialized type of thing.
> There definitely are axo-axonal synapses where the terminal of one
> axon synapses onto the axon terminal of another neuron.  These modify
> or modulate the synaptic potential that the post-synaptic neuron
> produces with a third cell.  That is, Cell B has a synapse with cell
> C.  Then cell A forms a synapse onto the presynaptic terminal of cell
> B and changes the magnitude of the synaptic potential that B produces
> in C.  Presynaptic inhibition is the most familiar case but there are
> many other examples.
> However this interaction is ordinarily a "normal" chemical synapse.  I
> don't know of any examples offhand where such an interaction is
> electrical, although such a thing is certainly possible.
> You are right in thinking that a synapse must ordinarily be within a
> short distance (a few space constants, to be precise) of the spike
> initiation zone in order to be effective.  That is because a synaptic
> potential ordinarily spreads with decay (electrotonically) and
> therefore gets weaker and weaker the farther it travels.  However even
> relatively small graded potentials do have important effects on the
> axon terminal in determining just how much synaptic transmitter to
> release so a synapse relatively close to a presynaptic terminal will
> have an effect.  Also, it is possible for an axon to start an axon
> potential anywhere along its length, as long as that section reaches
> threshold for one reason or another.  It is theoretically possible,
> though very unlikely, that a very strong electrical synapse from one
> axon to the middle of another will cause the postsynaptic cell to
> generate an action potential.  In this case, it is as if the cells
> were actually continuous so that the action potential just propagates
> from one to the other the same way it propagates down both sides of a
> branch  point.  There are also a tremendous number of cells with very
> short axons, less than a few space constants long, so that a synaptic
> potential produced anywhere along the axon will not decay that much as
> it spreads down the entire length of axon.
> I hope this helps and that it does not come so long after your
> question that you have abandoned all hope of getting an answer.

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