X-Message-Number: 25884 From: Date: Sat, 26 Mar 2005 01:43:27 EST Subject: Uploading technology (2.i.0). Uploading technology (2.i.0). In the first message of that set, I have broken the uploading aproach into 3 steps: - What to modelize ? - How to modelize it ? - On what technology (ies) implement it ? Here I take the first part of step two: As a first look, what has to be modelized fall into two domains: - Conduction of electrochemical potentials in axon (action potential), the neuron output, and in the dendrite tree, or neuron input side. - Very nonlinerar processing in the soma (body cell) and the synapse junction domain. This would include: Presynaptic axon terminal, postsynaptic dendrite spine head, and synaptic cleft with action of nearby glial cells. Here, I concentrate on the "simple" conduction problem. The first attempt was builtto explain electrochemical transmission in the axon. Because it looks as an electric cable in a liquid medium, the first model was derived from the submarine telegraph line mathematics framework. This is the so-called cable model of neural transmission. Next came in 1952 the work of A.L. Hodgkin, A.F. Huxley and B. Katz. This remains today a very good representation, unfortunately the "simple" conduction has turned into a set of four coupled differential equations, hard to solve for each small branch of the neuronal tree. It is not perfect neither: For example, it don't take into account the activation-inactivation coupling of Na channels. Temperature effects are not fully taken into account and membrane channels are assumed obey Ohm's law, not quite true in the real world. The best present day "simplified" solution seems to be the Hindmarsh-Rose model, first proposed in: Proc. R. Soc. London Ser.B vol.221, p. 87-102 in 1984. This two equation system has been upgraded to a three coupled differential equations in later works: Proc. R. Soc. London Ser.B vol. 225, p. 161-193 (1985) and: vol. 237, p. 267-288 followed by a second paper on pages: 289-312 in 1989. X.J. Wang has published too a contribution in Physica D, vol. 62, p. 263-274 in 1993. It seems that model would have to be chosen for a neural simulator. In most case, the action potential in the axon has no significant processing, it is merly data transmission. All the complexities are then "technology dependant" and come from the biochemical nature of the neuron. That has not to be simulated in uploading. The case for the dendrite side is quite different. Here, branching induce some important effects on the signal transmission. A dendridic tree is definitively not a simple branching conductor system. The physical nature of of the signal induces some processing with collective effects on connecting branches. 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=25884