X-Message-Number: 26933
From: 
Date: Mon, 5 Sep 2005 14:33:59 EDT
Subject: Uploading technology (1.i.2) The post synatic part.

Uploading technology (1.i.2) The post synatic part.

There are  symetrical, inhibitory synapses on dendrites, soma or the first 

part of the  axon, the hillock. The other class, the asymetric synapses include
all the  excitatory ones, mostly working with glutamate or aspartate. These 

are often on  dendritic spines. There is no spine without an excitatory synapse,
even if 10 15  percent include too a symetric, inhibitory component. The 
difficulty, for a  simulation come from the channel diversity. The synaptic 
functions to be  included at the postsynaptic level are:
-The channel famillies.
-The  spine.
-The receptor management.
Information input is not limited to the  presynaptics source:
Neurotransmitters come from both, the presynaptic  element and a more 

diffusive component from other synapses or gap junctions.  This is particularly 
true 
for second transmitters.
There are three potential  signals from the dendrite: The back propagating 
axion potential, the nearby  synapses potential and the ionic gap junctions on 
dendrites. All of that can be  summed up as a dendrite potential. Because of 
the small capacity of the synapse  membrane, there is no need for a separate 
work on slow and fast varying  potentials.

The dendrite input potential (DIP) is used such that on  flat synapses and 

must be processed for spines.  Depending on the spine  shape the potential will
not be the same at the head. So the DIP is processed  according the spine 
index (SInd).

Fast channels, tension gated or  main neurotransmitter gated ones are not 

modulated by second or third  transmitters on asymetric synapses, there is so a
symetry synapse index  (SymSInd). For example SymSInd = 0 for excitatory 

synapses, so all  neuromodulator effect is cancelled here. If SymSInd = 1, then 
this 
effect must  be taken into account.

A post synaptic head contains one thousand  or more channels, this is 
sufficient to smooth out any individual statistics and  there is no need for 

stochastic mathematical methods. That let neverthless a lot  of parameters from 
the 
channel diversity. G-protein and second messenger gated  channels are computed 
at the general computer level and enter here as a single  tension input, 

(CompTIn) included in the Computer Input (CompIn). CompIn may not  be actualised
at 
each computing cycle, so this parameter could be used for a  number of 

synapses, at each cycle, CompIn would refresh the data in a given  synapse, 
comming 

back to it after 128 cycles or more. CompIn would include  informations such as
produce or destroy x percent of a given receptor or act on  spine shape.

On the output side, there are 3 signals:
- The  potentials sent to the dendrite, one for each channel species (PotOut).
- The  back potential sent to the presynaptic part, using the gap junctions 
and  capacitive effect (BackPot).
- The  NO/CO gas sent to the presynaptic  part and nearby synapses.  This is 
modeled by a signal sent to the computer  level, the computer out (CompOut) 
answer to CompIn.
 
So we have on the input side:
The channels parameters, DIP, SInd,  SymSInd, CompIn including CompTIn.
On the output there are: PotOut (on the  order of 15 currents), BackPot, a 
single value and CompOut.

Yvan  Bozzonetti.



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