Need help on synapses.

Michael Ferber Ferber at zoology.uni-frankfurt.de
Sun Dec 10 07:10:01 EST 1995


In article <4aoe2oINNe60 at duncan.cs.utk.edu>,
   tzusheng at cs.utk.edu (Tzusheng) wrote:

Something cut
>
>Suppose that we have two neurons with synapses in between the two neurons.
>We feed an electric pulse into the presynaptic side of a synapse, and we get 
>a pulse from the postsynaptic side. 

Generally the pulse which leads to a synaptic transmission is an action 
potential. This usually always has the same size. At this point the 
information is coded in the frequency of the action potentials.

>I need to know if all the synapses in between the two neurons have the same, 
>similar, or quite different response (postsynaptic pulse) with the same input 
>pulse at presynaptic side. 

As far as I know the synapses between two neurones are similar in their 
properties, but depending on the spatial ditribution of the synapses they may 
contribute mor or less to the general postsynaptic potential. Note that there 
are many synapses between two neurones.

>If we take out different pairs of neurons from a part of the brain, such as
>hippocampal neurons from a rat, I need to know if synapses from different
>pair of neurons are different. 

I would expect this. You have neurones with different transmitters, which may 
be excitatory or inhibitory. Each single neuron receives input from many other 
neurones (up to 1000) which may use different transmitters and have different 
properties for the release of the transmitter (e.g longer or shorter time 
constants, amount of released transmitter)

>So the question can be reduced to: Are the synapses in the same functional 
>region of the brain homogeneous ?  If not, how different are they ?  It seems 
>to me that if they are quite the same, they don't process information much. 
>I might be wrong.  Thanks.

No, they are not! Furthermor you're really wrong with your suggestion that 
synapses do not contribute to information processing. Depending on the 
activity of the presynaptic neurone and the properties of the postsynaptic 
neurone you may have effects like facilitation (increasing amplitude of 
postynaptic potentials) simple summation of the potentials, anti-facilitation 
(a reduction in size of the PSPs) and other effect like post tetanic 
potentiation, habituation ...
In reality the synapse is a very important structure in the processing of 
information. 
For further information i suggest the reading of a text book on 
(neuro) physiology (e.g. From neuron to brain, Eds Nicholls J.G, Martin A.R. 
and Wallace B.G.)

Hope this helps
Michael 

>Any information would be greatly appreciated.
>
>--T. Pei

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|| Dr. Michael Ferber                     ||
|| Universitaet Frankfurt                 ||"science moves,
|| Zoologisches Institut                  || but slowly, slowly ......"
|| email: Ferber at zoology.uni-frankfurt.de ||                      Tennyson
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