Hi Laurent,
Delays can be of variable duration depending in part on the post
synaptic mechanisms involved.
For short delays (mseconds), the time course of depolarization can be
a factor. This has something to do with time constants and space
constants, the time it takes for postsynaptic potentials to develop
and the distance currents must travel to reach biosensing components
(such as voltage sensitive ion channels). Frankly, this is
biophysics and beyond my keen.
For longer delays, seconds and longer, metabolic events such as
phosphorylation/dephosphoylation reactions linked through GProteins
and other second messenger systems can produce postsynaptic responses
long, long after a synaptic event. This is biochemical (at least in
my primitive construct of life in reduction).
rlh
At 5:09 PM +0200 07/16/02, Laurent wrote:
>Thanks a lot.
>Anyway, I may have not explain correctly what I wanted, or I don't
>understand well enough what you say.
>>I have some basic notions about neurons and chemistry, but I haven't tried
>to know the whole phenomena of the synapse.
>>Here is what I wanted know if it was possible :
>>Neuron A is activated since a few msec (or less or even more).
>Neuron A suddenly desactivates.
>Wait some msec.... (delay, no signal in A's axon, nor through Synapse S)
>Synapse S from neuron A (still desactivated) to neuron B then transmits a
>signal.
>>Is that the same delay you were talking about ?
>>If this is possible, can the delay be very long ?
>>Laurent
>>>"Richard S. Norman" wrote:
>>> On Tue, 16 Jul 2002 15:24:03 +0200, Laurent
>> <lorseau at ens.insa-rennes.fr> wrote:
>>>> >Hi !
>> >
>> >I was wondering if a natural synapse could transmit a signal after and
>> >only after (and not instantly after) the source neuron has stopped being
>> >activated. Is this possible ?
>> >
>> >Laurent.
>>>> Your question can be answered on many different levels of detail. How
>> much neurophysiology background do you have and how much detail do you
>> want? Are you really asking about synaptic delay?
>>>> Generally, the synapse releases transmitter as a result of being
>> depolarized. In many cases, that means that the axon has just fired
>> an action potential. The nerve activity causes the transmitter
>> release by starting a complex process involving calcium and vesicle
>> changes (here is where all the details occur).
>>>> It does take a brief time to crank up the machinery and here is where
>> most of the synaptic delay occurs. But if the action potential is
>> prolonged a bit, it is certainly possible for the transmitter to be
>> released before the action potential is finished, if that is what you
>> are asking. The delay can vary from a few hundred microseconds to a
>> msec or more depending on the cell and the synapse and the action
>> potential can have a similar variation in duration.
>>>> The most important thing is the the release machinery does not require
> > that the depolarization be removed before release can occur. So, yes,
> > it is possible.
--
Richard L. Hall
Associate Professor of Animal Physiology
University of the Virgin Islands
St. Thomas, VI 00802
340-693-1386
"Live life on the edge. The view is always better." rlh
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