Ranvier's nodules: what they are and how they serve neurons

Ranvier's nodes are cellular substructures that are part of the neuronal system. Among other things, they are responsible for regulating electrical signals between neurons, that is, they are a very important part of maintaining the activity of the nervous system.

In this article We will see what Ranvier's nodules are, what are their main functions and what pathologies of the nervous system have been associated with them.

• Related article: "Types of neurons: characteristics and functions"

What are Ranvier's nodules?

Ranvier's nodules, or Ranvier's nodes, are small openings found interspersed between the myelin sheaths that cover neuronal axons.

To explain it better, let's go in parts: among other things, the nervous system of vertebrates is made up of long propagations of neurons that are connected to 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 spreads through the neural network.

In turn, the axons are covered by a thick layer of fatty substances and proteins called "myelin." This thick layer has the shape of a sheath whose function is

stimulate the transmission of nerve impulses between neurons. What myelin does is protect the neural network; it serves as an insulator that accelerates nerve transmission between axons.

These myelin sheaths or layers are not uniform or completely smooth, but instead are composed of by small depressions 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 subsidences are known as Ranvier nodules or nodes.

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Its duties?

Ranvier's nodes are essential for maintaining the function of myelinated axons. They are parcels of a very small length that allow contact between the axon and the extracellular space, and with this, they make possible the entry of electrolytes of sodium, potassium, and other chemical elements.

In very broad terms, Ranvier's nodes facilitate the expansion of electrical impulses that we call the "action potential" and they 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 kind of grooves that are interspersed in the axon, Ranvier's nodules allow electrical activity to transit as small hops between node and node until reaching the neuronal nucleus. The latter accelerates the speed of communication between neurons, that is, the synapse, which makes 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 Ranvier's nodules can cause great modifications in the action potentials, and with this, in the activity of the system highly strung. The latter has been especially related to the elements that make up the nodes.

Ranvier's nodes are composed of channels that allow the passage of substances necessary to maintain electrical activity, especially potassium and sodium. These channels experience the full voltage change in membrane action potentials. This is why Ranvier nodes are areas heavily populated with protein material.

It is a necessary condition that there is a sufficient number of channels to avoid failures in the propagation of electric current. In other words, 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

For these nodes to form and function properly, a series of rather complex interactions have to occur between the axon and the cells that line it.

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

Among other things, these pathologies have the common characteristic that a demyelination process occurs (the damage that occurs in the myelin sheaths that cover the axons). demyelination causes electrical activity to change significantly, slowing down the impulse and response, and in some cases causing them to even be lost. The consequence is a disorganization of the nervous system.

The conditions to which the functioning of Ranvier's nodules has been associated are very diverse and are still under study. They have been related since Autism Spectrum Disorder, different Epilepsy Syndromes and the 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.