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. Content-Type: text/html; charset="US-ASCII" [ AUTOMATICALLY SKIPPING HTML ENCODING! ] Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=26930