For more than 70 years, biologists and biophysicists have been trying to unravel the mystery surrounding the saltatory conduction of so-called myelinated neurons. This conduction is indeed very different and faster than for fibres “without” myelin. Many theories have been developed. Albert Einstein used the metaphor of the train to explain the theory of relativity. It is also possible to use a similar metaphor to better understand this transient functioning of the neuron: the transmission of the action potential in myelinated fibres. By studying the various theories that have been put forward and confronting them with physics, mathematics and microscopic anatomical observations, it is possible to refute or confirm certain hypotheses. It is easy and simple, then, to demonstrate unequivocally that the action potential cannot, in any way, jump from node of Ranvier (noR) to node of Ranvier as has been assumed and taught until now. It is possible to describe that the neuron uses an elegant and very simple method to increase the speed of transmission of the neuronal message. It is also important to conclude that this increase in speed, contrary to common belief, has an energetic cost that is greater than expected and that is proportional to the speed and in perfect agreement with the laws of thermodynamics.