So the loop is closed. The answer is simple. They are not able to lead electric current for longer distances. The impulse travelling through axon is not able to go more than 0.1mm distance. The segments in axons restore impulse size.
Biological conductors are very bad comparing to metal wires.
However they have other advantages. The process that works as it has been depicted herein compares to analog computers. Therefore I assume that brain works like analog computer. Analog computers have been designed to process differential equations. The circle in our explanation is closed as well system of coding and decoding in the brain.