Nodes of Ranvier: what are they and how do they serve neurons?

This part of the axons of neurons allow the electrical impulse to propagate well.

The nodes of Ranvier are cell substructures that are part of the neuronal system. Among other things, they are responsible for regulating the electrical signals between neurons, i.e. they are a very important part of maintaining the activity of the nervous system.

In this article we will see what the nodes of Ranvier areWhat are their main functions and what pathologies of the nervous system have been associated with them.

What are the nodes of Ranvier?

The nodes of Ranvier, or nodes of Ranvier, are small openings that are found intercalated between the myelin sheaths that cover the neuronal axons. covering the neuronal axons.

To explain it better, let's take a step-by-step approach: among other things, the vertebrate nervous system is composed of long propagations of neurons that connect with each other. These propagations are called "axons", they arise from the soma (the body) of the neuron and have the shape of a cone that elongates as it extends through the neuronal network.

In turn, the axons are covered by a thick layer of fatty substances and proteins called "myelin". This thick layer has the form of a sheath whose function is to stimulate the transmission of impulses. stimulate the transmission of nerve impulses between the neurons.. What myelin does is protect the neuronal network; it serves as an insulator that accelerates nerve transmission between axons.

These myelin sheaths or layers are neither uniform nor completely smooth, but are composed of small sinks or grooves interspersed along the axon, which we call nodules or nodes. The first to describe both myelin and its nodes was the French physician and histologist Louis-Antoine Ranvier in 1878. That is why to this day, these sinks are known as nodes or nodes of Ranvier.

What are their functions?

The nodes of Ranvier are essential for maintaining the function of myelinated axons. They are plots of a very small length that allow the contact between the axon with the extracellular spaceThey allow the entry of sodium, potassium, electrolytes and other chemical elements.

Broadly speaking, the nodes of Ranvier facilitate the expansion of the electrical impulses that we call "action potential" and allow the electrical activity that passes through the axons to be maintained at an adequate speed until it reaches the body of the neuron.

Being a sort of grooves that are interspersed in the axon, the nodes of Ranvier allow electrical activity to travel in small jumps from node to node until it reaches the neuronal nucleus. until it reaches the neuronal nucleus. The latter accelerates the speed of communication between neurons, i.e., the synapse, thus making it possible for all the activity associated with the brain to take place.

Other characteristics of the nodes

It is now known that small changes in the functioning of the nodes of Ranvier can cause large changes in action potentials, and with this, in the activity of the nervous system. The latter has been related especially to the elements that compose the nodes.

The nodes of Ranvier are composed of channels that allow the passage of substances necessary to maintain electrical activity, especially potassium and sodium. In these channels, the total voltage change in membrane action potentials is experienced. This is why the nodes of Ranvier are highly populated highly populated areas of protein material.

It is a necessary condition that a sufficient number of channels are present to avoid failures in the propagation of the electric current. That is to say that a significant number of channels is necessary to ensure the rapid activation of the channels, and with this, the action potentials.

Diseases and related medical conditions

In order for these nodes to form and function properly, a series of rather complex interactions between the axon and the cells that cover it must occur.

The complexity of these interactions between the nodes and the regions around them makes it possible to develop pathologies of the nervous system associated with the functioning of the nodes and, more specifically, related to the functioning of the channels that allow the entry of substances and electrical communication.

Among other things, such pathologies have the common characteristic that a process of demyelination (the damage that occurs in the myelin layers that cover the axons) occurs. Demyelination causes that the electrical activity is modified in an important wayThe demyelination causes the electrical activity to change significantly, reducing the speed of the impulse and the response, and in some cases even causing them to be lost. The consequence is a disorganization of the nervous system.

The conditions to which the functioning of Ranvier's nodes has been associated are very diverse and are still under study. They have been related from Autism Spectrum Disorder, different Epilepsy Syndromes and fibromyalgia, to autoimmune disorders such as Guillain-Barré Syndrome.

Bibliographic references:

• Arancibia-Carcamo, L. and Attwell, D. (2014). The node of Ranvier in CNS pathology. Acta Neuropathologica, 128(2): 161-175.