X-Message-Number: 26930
From: 
Date: Sun, 4 Sep 2005 13:15:24 EDT
Subject: Uploading technology (1.viii.1) Channel diversity (4 slow chemicals). 

Uploading technology (1.viii.1) Channel diversity (4 slow  chemicals).

Slow channels are not open "from the outside" by a  conformational change 
produced by a fixed neuromediateur, they are open from the  inside face of the 
membrane. There are two possibilities:
 
1/ A receptor, when linked to a neuromediator on the outside activate on  the 
inside a so-called G-protein, this one will open the channel. Changing the  
receptor, not the channel, produce different sensitivity to different  

neuromediators. There are more than 1 000 different receptors. Most of them  
react to 
more than one neuromediators. The most common case is a main  neuromediator 
and a secondary, modulating one. there may be three neuromediators  : One 
principal and two modulators.
 
Because the neuromediator(s) don't link directly to the channel, there is a  
small delay in the action. In most case, the channel remains open for a long  
time, up to seconds and more. It seems not useful to compute their current 
every  millisecond. Sampling could be done on a far more coarse time scale. A 
general  purpose computer could do the job.

2/ An even slower system use a  second messenger inside the cell. The 

receptor receive one or more  neuromediators and then activate one or more 
secondary 
messengers on the inside  membrane face. This catalytic action may produce 
many molecules and so amplify a  signal. The secondary messengers are then 

distributed actively or passively by a  diffusion process until they are 
destroyed 
or encounter a receptor.  this  system can activate different receptors in 

different places. These receptors can  open a channel or direct the synthesis or
processing of proteins. Such a signal  could for example order the production 
of new channels from mRNA by the  ribosomes or destroy them by boosting the 

degradation enzyme production. It  seems , in the soma at least, these secondary
or tertiary messengers use a  common  pathway based on cyclic AMP. The effect 
may extend over seconds,  minutes or even hours. Clearly, this is not an 

information about exterior  events, it is a structural control system intendend 
to 
adapt the neuronal  network at a set of particular conditions. This would too 
being taken in charge  by a general purpose computer outside the fast running 
neuromorphic  chip.

Yvan Bozzonetti.



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