From: Martin Striz (mstriz@gmail.com)
Date: Wed Apr 12 2006 - 13:08:10 MDT
On 4/12/06, Richard Loosemore <rpwl@lightlink.com> wrote:
> Net benefit from this? Not very susceptible to static electricity.
> Great for keeping your brain stable in the face of a rather staticky
> world.
Is the natural world really that staticky? Take away all the
electricity that we artificially pump into our environment, and it's
not that staticky.
> Another benefit, perhaps: whereas an electrical signal is
> somewhat passive and might therefore degrade with distance travelled,
> the action potential is actively promoted by the energy locked up in the
> neural fiber ... so it travels without loss of strength.
This is a great advantage of voltage propagation through ion channels
over current through wires. Every current-carrying wire has some
minimal level of resistance, so you lose signal strength over large
distances. However, there wouldn't be a selection pressure for it in
the evolution of nervous systems. Most neuronal axons are less than a
millimeter to a few centimeters. In humans, the longest nerve is
about a meter. But humans didn't evolve nervous systems first.
Something more akin to flatworms did. They are only a few millimeters
long. Signal strength loss wouldn't be an issue.
The more likely reason why neurons are built the way they are is that
ions were readily available to be exploited by primitive organisms.
Ionic gradients make electrical gradients. Building a
current-carrying system takes too much planning. You can't boostrap
your way to it. The fitness gradient to the finished product is not
smooth. That's why carbon nanotubes never evolved in nature either.
> As for having lots of neurotransmitters, it might turn out to be the
> case that this is a way to implement several different functional
> influences on the process of thinking. For example: allow the system
> to do multiple relaxation along several dimensions simultaneously. Now
> I don't know if that is how they are used, but it is a possibility, and
> it might work very well.
Again, that can be done with receptors or wiring alone, if you want to
be parismonious. The more likely reason is that each neuronal
subsystem evolved in response to environmental pressures
independently, randomly utilizing one particular molecule or another
as the transmitter. Unfortunately, again no planning.
> Bottom line: might not be a good idea to second guess nature's designs
> until we're very sure we know exactly how the thing works.
I'll do it anyway. ;-)
Martin
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