question about potential distribution in axon and synapses

Larry Lart larrylart at dol.ie
Thu Jun 13 13:04:59 EST 2002






> Your questions indicate you inow some things about neurons but perhaps
> just a little?  What is your background?



Is not neurophysiology anyway ... is just a life time hobby for me :) I an
in computers science/AI but I used (and lately more) to turn towards
neurophysiology. just looking for answer/ideas for implementation. I hope
you guys don't mind even sometimes my questions sounds a bit "to basic" but
in fact I just need clarification .

there is so much information out there and so many point of view that makes
it difficult for me sometimes to get a final answer.



>Have you read any books on
> basic neurophysiology?



Yes, I did.



> The voltage in the soma really isn't relevant to anything.  Synaptic
> input generates electrical potentials in cells.



I thought that neuron's soma is responsible for threshold value and
triggering the firing process?



> spread passively (electrotonically) down dendrites which are
> usually electrically inexcitable.



? I was reading(again somewhere ... i don't remember exactly in what
document) that dendrites are not just "gathering" the signal but they can
even amplify the signal down to the cell body.



>But the axon (and perhaps the
> cell body)



Perhaps the cell body(soma) ? Again. I thought that the main "excited" part
in the firing process is the cell body and axon is responsible just to
propagate signal down to synapses...




> In that case, the potential propagates actively without decay along
> all the electrically excitable axons.
>
> Activity at synapses can be very variable (plastic).  The "strength"
> of a synapse, that is, the amount of transmitter released, is graded
> with the amount of depolarization at the synapse.  But usually a
> synapse is at the end of an axon and so is activated by an "all
> or nothing" action potential, so the amount of transmitter release is
> then "all or nothing".



yes . but here is my question "all or nothing from what?" you can have all
of nothing from 1 = 2 or from 2 = 2...



.  The activity at one synapse stimulates
> second messenger events inside the postsynaptic cell which causes
> changes in the excitability of that cell, possibly including the
> response to a different synapse.



"possibly"?



>It is also possible for simultaneous
> activity at two different synapses to produce long-term changes in
> the synaptic strength.
>



ok. I know that it's possible but I want more specific information.


> Your question about "dead end" axons doesn't really make much sense.
> There is no potential "waste" and I really don't know what you mean
> by "environment conductivity".



I meant the terminal buttons. Ok I suppose the neurons are floating in
whatever liquid fills the inter-neuronal space (they not in vacuum right? J)
I don't know the electrochemical properties(it should have a level of
conductivity in order to facilitate synapses?) of this liquid but I suppose
that there is a small depolarisation between terminal buttons and this
"liquid" ?

That might explain(evolutionary) the myelin sheath?

I just need to make a balance of those potentials. On the other side I want
to get answer about how much is the neuronal cell responsible for signal
propagation.



Larry Lart








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