Nature solved this problem for us by developing myelinated axons carry our nerve impulses to body extremities. Covering the whole surface of our fibers, save for the very small (1 micron long and 10 microns in diameter) nodes of Ranvier, the myelin essentially insulates the axon surface. It consists of hundreds (I use 200 in most simulations) of wraps passive membrane. Each wrap produces a proportional increase in the resistance of the underlying membrane and a reciprocal decrease in the membrane capacitance per unit area.

The net effect of this wrapping is to restrict generation of action potentials to the nodes. Thus impulses essentially jump from node to node (saltatory -[Latin saltitorius , to "dancing" - conduction) This means that an active node essentially supplies only the energy to depolarize the next node and little charge to depolarize the very low capacitance of the myelinated internode. The net effect is that the velocity in such fibers is very fast, approximately that of the squid giant axon. Furthermore, because the surface-to-volume ratio becomes increases inversely with the diameter of a fiber, the energy consumed by a propagating impulse in unmyelinated axons of a few microns would be enormous. Thus the myelination not only provides a much faster propagation of impulses but also makes the net ionic withdraw from the ion concentration battery stores far less, a much more efficient system.

Extensive simulations of saltatory conduction have been carried out in my lab in an effort to evaluate the contributions of the various parameters to the velocity of the impulse. Systematic variations of parameters revealed that the velocity was