Saturday, February 17, 2007

Who put the action in Acton Potentials

Dear Science Salon Denizens (SSDs from now on... we scientists & engineers love our acronyms & jargon):

This post is the promised follow-up to yesterday's Salon. Mainly I am putting it here so you (the SSDs) can send me feedback wrt (with respect to) how you thought the session went.

The goal of my talk yesterday was to arm you with some concepts and termnology so that you can begin to read some of the posted articles. The concepts included:

1. An introduction to the neuron, one of the thousands of specialized cell types in the body. As we discussed, the neuron is the fundamental unit of signal transmission throughout the nervous system.

Nota bene: There are many exceptions to this last statement. But remember I warned you my teaching style is based on a series on benign lies whereby I tell you something that is not completely true in order to get a primary concept across... later I say "that wasn't exactly true". And then I tell you the next benign lie.

In fact, the neurons have an enormous amount of help in signal transmission. Even their primary function - the propagation of the action potential- cannot be accomplished without specific companion cells. But for now I won't burden you with the names of any more cell types.

2. An introduction to neural transmission which is part electrical and part chemical. Just for fun I will tell you that, in fact, BOTH the electrical and chemical signal transmission components are simply different manifestations of the same driving force... a force called the Gibbs Free Energy. The only thing of importance we really do as life forms, is extract and store energy. This is not easy in a hostile, highly entropic universe and it is the true and only magic trick of life. Once we have this energy, we are free to use it to maintain and propagate ourselves as life forms. Hence, the concept of 'Free Energy': as in free to be applied to useful work... not free as in 'at no cost'. Both the electrical and chemical components of signal transmission in a neuron are powered by Free Energy.

The full name for the Free Energy that drives electrochemical reactions such as propagation of the action potential is Gibbs Free Energy named after the great (and I do mean genius-level great) physical chemist J. Willard Gibbs. Gibbs was the classic mad genius who basically lived in a broom closet-sized office at Yale or Princeton (I forget) for his entire academc career. The fameous (non-scientific) story about him is that although he attended every faculty meeting for something like 30 years he never uttered a word... except once. At one meeting a motion was made to elimate the mathematics requirement in favor of a language requirement (or some such). As legend has it, Gibbs raised his hand, was recognized by the Chair, and said, "But gentlemen mathematics is a language.", then sat back down. End of story. But old J. Willard received the highest honor science has to offer (and it's not the Nobel Prize). He has a basic unit of physical measurement named after him. The unit of Gibbs Free Energy is right up there with an Einstein of photons, a Curie of radioactive disintegrations, and -of course- a Newton of force.

3. We also briefly reviewed the rudimentary structure of a neural network, i.e. head to tail, presynaptic to post synaptic. Dendrites on the back side, axons on the front side.

4. We took a look at brain complexity and and ran a few numbers get an idea of how many neurons, how many synaptic connections, and how many signals per second per whole brain.

These calculations and all the rest of it led to a final generalization of how whole-brain scans work. If one area of the brain is signaling like crazy lots of neurons will be sending lots of action potentials which means they will need lots of Gibbs Free Energy which means the burning (metabolism of) lots of sugar, which means a requirement for lots of oxygen-carrying blood, which means the blood supply to that region will spike. If we can follow changes in blood supply or any related parameter in real time by MRI, PET or other scan technology we can begin to correlate regions of the brain with specific aspects of consciousness as well as other subconscious brain-controlled functons (musical genius, sociopathy... you fill in the blanks).

5. Finally we looked at a lot of cool and very beautiful images. Never a waste of time.

Cheers, Dr. G

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