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Saltatory Conduction

This page offers a metaphor for understanding how myelin speeds up the propagation of action potentials.

There should be animated cartoons here (swf files), to make the description more intuitive.
Hopefully these animations will one day reappear at this site (as gif files).

Imagine a very long, thin water-balloon lying on the ground in front of you.  The balloon represents an UN-myelinated axon.

Now imagine another water-balloon enclosed within long, tight-fitting segments of pipe.  In between the segments of pipe are short stretches, about as wide as your foot, where the balloon is naked.  Now the balloon represents a myelinated axon; the pipe is myelin and the short naked stretches correspond to nodes of Ranvier.

BACKGROUND and EXPLANATION:  This metaphor may appear silly, but the physics is actually plausible.  It is based on a respectable hydrodynamic model for electricity, in which water pressure corresponds to voltage, flowing water corresponds to electric current, and elasticity of the balloon corresponds to capacitance. 

David KingComments and questions:

SIUC / School of Medicine / Anatomy / David King
Last updated:  15 October 2022 / dgk