In fact, perhaps you are overweight because of a lack of myelin . . .

"What does myelin do?

Myelin speeds the conduction of nerve impulses by a factor of 10 compared to unmyelinated fibers of the same diameter. This increases the nervous system's information processing speed and delivery, decreasing reaction times to stimuli, increasing temporal precision, more closely synchronizing spatially-distributed targets (e.g. different regions of a muscle sheet) and providing for shorter delays in feedback loops, increasing their intrinsic stability.

Myelin has other advantageous characteristics. It confers a several hundred-fold improvement in metabolic efficiency for recouping the energy cost of nerve impulse traffic. For a nervous system such as ours, which already accounts for an age-dependent 20-50% of the body's resting metabolic energy budget, this is not an inconsequential advantage. Were we a non-myelinated species, we would have greatly diminished problems with being overweight!"

(That's my story, and I'm sticking to it. :-) )

http://www.pbrc.hawaii.edu/~danh/Inv...te_myelin.html

A simple explanation of myelin:

"... think of a nerve as a copper cable. If you run a current through it, it travels at a certain speed across the cable depending on the internal resistance of the cable. Different elements have differrent cunduction speeds.

Anyway, physicist have known a trick for a while now that helps in increasing conduction speeds. The way to do this is instead of having an uninsulated wire, you insulate the wire but leave gaps in the insulation to allow the current to actually jump across the insulated part to the next gap. This increases the speed of cunduction by a large amount, and this is what the myelin sheath actually does.

Also, a neat little fact is that the myelin sheath acts as a scaffolding for damaged neurons, which allows them to regenerate. Non myelinated neurons are screwed once they are damaged, and do not regenerate."

http://au.answers.yahoo.com/answers2...AA3P2La&show=7

Here's a pretty picture:

http://images.google.com/imgres?imgu...LR:en%26sa%3DN

Cherie