Re: where do copies come from?

From: George Levy <glevy.domain.name.hidden>
Date: Mon, 11 Jul 2005 22:38:35 -0700

Stathis Papaioannou wrote:

> The ionic gradients across cell membranes determine the transmembrane
> potential and how close the neuron is to the voltage threshold which
> will trigger an action potential by opening transmembrane ion
> channels. Other factors influencing this include the exact geometry of
> the neuron and composition of the cell membrane (which determines
> capacitance and the shape and speed of propagation of the action
> potential), the number, type and location of voltage-activated ion
> channels, the number, type and location of various neurotransmitter
> receptors, the local concentration of enzymes that break down
> neurotransmitters, and many other things besides. The ionic gradients
> across cell membranes (all cell membranes, not just neurons) are
> actively maintained within tight limits by energy-requiring
> transmembrane proteins, such as Na/K ATPase, and if this suddenly
> stops working, the cell will quickly die. The moment to moment
> variations in ion fluxes and membrane potential may be allowed to
> collapse and the neuron will remain structurally intact, so to this
> extent the exact cellular chemistry may not be necessary for long term
> memories. However, all the other things I have mentioned are important
> in determining the "wiring diagram and strength of connections", and
> could easily be maintained over decades. Look up "action potential" in
> Wikipedia, and think about how you would design an equivalent circuit
> for even one neuron. It may be a ridiculously complex way to design a
> computer that would be able to run and maintain a human body, but
> whereas I would happily trade my heart or my kidneys for more
> efficiently engineered models, I would like any brain replacement to
> be an exact functional analogue of my present one.


Stathis,

you don't have to get down to that level of complexity. As long as the
high level function remains the same, you can still say "yes doctor" to
a substitution experiment. Example: artificial eye lenses made of
plastic and not of tissue, prostheses made of titanium steel and not of
bone.

George
Received on Tue Jul 12 2005 - 01:47:23 PDT