RANVIER NODULES: WHAT THEY ARE AND THEIR FUNCTIONS - GEOGRAFÍA - 2025

The nodes of Ranvier are a number of interruptions that originate at regular interval along the length of the axon of a neuron. They are small nodules that occur in the myelin sheath (a layer of white matter) that surround the axons of neurons.

Ranvier's nodules are characterized by being very small spaces. Specifically, they have a dimension of one micrometer. Likewise, these nodules are exposed to the membrane of the axon to the extracellular fluid, and serve so that the nerve impulse transmitted between neurons moves with greater speed, in a saltatory way.

Typical myelinated nerve where the location of the nodules of Ranvier can be seen.

In this article, the main characteristics of Ranvier's nodules are reviewed and their functional relationship with the speed of synaptic transmissions between neurons is discussed.

Characteristics of Ranvier's nodules

The nodules or nodes of Ranvier are small interruptions that some neurons present in their axons.

These nodules were discovered by the French anatomist Louis-Antoine Ranvier at the beginning of the last century and are one of the basic elements of myelinated synaptic transmissions.

In fact, the formation of these small jumps located in the axon of the neuron (the region of the cell responsible for transmitting information) is highly linked to the myelin sheath.

The myelin sheath is a multilayered structure formed by the plasma membranes that surround the axons. It is made up of lipoprotein material that forms some phospholipid bilayer systems.

When this sheath attaches to brain cells, it generates the well-known white matter neurons. These types of neurons are characterized by faster synaptic transmission than the others.

The increase in the transmission speed is generated mainly through Ranvier's nodules that originate in the myelin-coated axons of neurons.

In this sense, the nodules of Ranvier give rise to a saltatory transmission, which increases the speed of the circulation of nerve impulses.

Functions of the nodules of Ranvier

Ranvier's nodules. Source: Marek M / Public domain

Ranvier's nodules are small grooves generated in the axons of neurons that mainly affect synaptic transmission.

Synaptic transmission or synapse is the exchange of information that neurons carry out with each other. This exchange of information gives rise to brain activity and, therefore, to all the functions controlled by the brain.

In order to carry out this exchange of information, neurons give rise to the activity known as the action potential. This intracerebral phenomenon originates the synaptic transmission itself.

Generation of action potentials

Action potentials constitute a series of physiological responses of neurons that allow the nerve stimulus to spread from one cell to another.

Specifically, neurons are in an ionic environment of different charge. That is, the intracellular space (inside the neuron) presents an ionic charge different from that of the extracellular space (outside the neuron).

The fact that the two charges are different separates the neurons from each other. That is, in resting conditions, the ions that make up the neuron's inner charge cannot leave it and those that make up the outer region cannot enter, thus inhibiting synaptic transmission.

In this sense, the ion channels of neurons can only open and allow synaptic transmission when certain substances stimulate their ionic charge. Specifically, the transmission of information between neurons is carried out through the direct effect of neurotransmitters.

Thus, for two neurons to communicate with each other, it is necessary the presence of a transporter (the neurotransmitter) that travels from one neuron to the other and, in this way, performs the exchange of information.

Propagation of action potentials

The neuronal activity discussed so far is identical both for neurons that contain Ranvier's nodules and for neurons that do not have these small structures.

Thus, the effect of Ranvier's nodules occurs once the action potential has been realized and the information must travel through the interior of the cell.

In this sense, it is necessary to take into account that neurons capture and send information through a region that is located at one of its ends known as dendrites.

However, the dendrites do not elaborate the information, so to complete the transmission of information the nerve impulses must travel to the nucleus, which is generally at the other end of the neuron.

To travel from one region to the other, information must travel through the axon, a structure that links the dendrites (which receive the information) with the nucleus (which makes the information).

Axons with nodules of Ranvier

Ranvier's nodules produce their main effects in the information transmission process that takes place between the dendrites and the nucleus of the cell. This transmission is carried out through the axon, the region of the cell where Ranvier's nodules are located.

Specifically, nodules of Ranvier are found in axons of neurons covered with myelin sheath. Said myelin sheath is a substance that generates a kind of chain that runs through the entire axon.

In order to illustrate this more graphically, the myelin sheath can be compared to a necklace of macaroni. In this case, the entire collar would be the axon of the neuron, the macaroni themselves the myelin sheaths and the thread between each macaron would be the Ranvier's nodules.

This different structure of the axons allows that the information does not have to pass through all the regions of the axon to reach the nucleus of the cell. Rather, it can travel by saltatory transmission through the nodes of Ranvier.

In other words, the nerve impulse travels through the axon "jumping" from node to node, until it reaches the nucleus of the neuron. This type of transmission allows to increase the speed of the synapse and gives rise to a neuronal connection and a much faster and more efficient exchange of information.

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