Nerve impulses travel in a “dual cable” with myelin, playing additional roles to what was previously thought, new research has found. This discovery advances human knowledge of how brain connections work, and may help scientists understand more accurately what happens when myelin is lost — which is what occurs in diseases like multiple sclerosis (MS).
The study reporting the findings, titled “Saltatory Conduction along Myelinated Axons Involves a Periaxonal Nanocircuit,” was published in the journal Cell.
Myelin serves as a kind of electrical insulator that makes nerve impulses travel fast, so as to maintain high-speed communication between nerve cells, across the peripheral and central nervous systems (brain and spinal cord). In most densely myelinated axons, the conduction velocity can reach 70–120 meters per second, the speed of a race car.
At the basis of this rapid conduction are myelin-free gaps, called nodes of Ranvier, placed along the axon.
Nerve impulses, known as action potentials, can propagate quickly along the axon because they “jump” from one node of Ranvier to the next, a process known as saltatory conduction. An impulse jumps from node to node down the full length of an axon, speeding its arrival and transmission to the next nerve cell, compared with action potentials that travel along unmyelinated axons.
Scientists have known about this process for many decades. But they had been missing, until now, one piece of the detailed picture of how these electrical circuits take place, and what happens when myelin is damaged, such as in demyelinating diseases like MS.
While the view that myelin is an insulator with minimal or no electrical activity had been widely accepted, some scientists have proposed alternative models in which impulses can actually travel inside myelin or just below it.
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