Ranvier nodes are cellular substructures that are part of the neural system. Among other things, they are responsible for regulating 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 Ranvier’s nodules are, what their main functions are and what nervous system pathologies have been associated with them.

What are Ranvier’s nodes?

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

To explain it better, let’s go by parts: among other things, the nervous system of vertebrates is composed of long propagations of neurons that connect 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 lengthens 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 is in the form of a sheath whose function is to stimulate the transmission of nerve impulses between the neurons . What myelin does is protect the neural network; it serves as an insulator that accelerates nerve transmission between the axons.

These sheaths or layers of myelin are not uniform or 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 historian Louis-Antoine Ranvier in 1878. That is why, to this day, such collapses are known as Ranvier’s nodules or nodes.

What are its functions?

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

In very broad terms, Ranvier’s nodes facilitate the expansion of electrical impulses that we call “action potential” and allow the electrical activity passing through the axons to be maintained at an adequate speed until it reaches the body of the neuron.

Being a kind of groove interspersed in the axon, Ranvier’s nodules allow electrical activity to pass as small jumps between node and node until reaching the neuronal nucleus. The latter speeds up the communication between neurons, i.e. the synapse, 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 Ranvier’s nodules can cause large changes in action potentials, and with this, in the activity of the nervous system. The latter has been especially related to the elements that make up the nodes.

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

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It is a necessary condition that there are a sufficient number of channels to avoid failures in the propagation of the electrical current. This means that a significant number of channels are 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 fairly complex series of interactions must occur between the axon and the cells lining it.

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

The conditions with which Ranvier’s nodules have 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.