por What are Ranvier’s nodules?
The Ranvier’s nodules They are a series of interruptions that originate at regular intervals along the axon of a neuron. Is about small nodules that occur in the myelin sheath (a layer of white matter) that surrounds the axons of neurons.
Ranvier’s nodules are very small spaces. Specifically, they have a dimension of one micrometer.
Likewise, these nodules are exposed to the axon membrane to the extracellular fluid, and they serve so that the nervous impulse transmitted between neurons moves with greater speed, in a saltatory way.
Characteristics of Ranvier’s nodules
– Ranvier’s nodes or nodes are small interruptions that 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.
– The formation of these small jumps located in the axon of the neuron (region of the cell responsible for transmitting information) is highly linked to the myelin sheath.
– The myelin sheath is a multilaminar structure formed by the plasmatic membranes that surround the axons. It is made up of lipoprotein material that forms some phospholipid bilayer systems.
When this sheath adheres to brain cells, it generates the well-known white matter neurons. This type of neurons are characterized by presenting a faster synaptic transmission than the others.
– The increase in transmission speed is generated mainly through Ranvier’s nodes, which originate from the myelin-coated axons of neurons.
– Ranvier’s nodules give rise to a saltatory transmission, which increases the speed of circulation of nerve impulses.
Functions of Ranvier’s nodes
Ranvier’s nodules are small grooves generated in the axons of neurons that mainly affect synaptic transmission.
Synaptic transmission or synapses 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 action potential, or electrical signals. Said 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 propagate from one cell to another.
Specifically, the neurons are in an ionic environment of different charge. That is, the intracellular space (inside the neuron) has a different ionic charge than the extracellular space (outside the neuron).
The fact that the two charges are different separates the neurons from each other. That is, under resting conditions, the ions that make up the inner charge of the neuron cannot leave it and those that make up the outer region cannot enter, thus inhibiting synaptic transmission.
In this sense, the ionic 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 be able to communicate with each other, the presence of a transporter (the neurotransmitter) is needed that travels from one neuron to the other and, in this way, carries out the exchange of information.
Propagation of action potentials
The neuronal activity discussed so far is identical both for neurons that contain Ranvier nodules and for neurons that do not present these small structures.
Thus, the effect of Ranvier’s nodules occurs once the action potential has been carried out 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 their ends, known as dendrites.
However, the dendrites do not process information, so to complete the transmission of information, 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, the information must travel through the axon, a structure that joins the dendrites (which receive the information) with the nucleus (which produces the information).
Axons with Ranvier nodes
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 the Ranvier nodules are located.
Specifically, Ranvier’s nodules are found in axons of neurons covered with a myelin sheath. Said myelin sheath is a substance that generates a kind of chain that runs through the entire axon.
To be able to exemplify it in a more graphic way, the myelin sheath can be compared with a necklace of macaroni. In this case, the collar in its entirety would be the axon of the neuron, the macaroni itself the myelin sheaths, and the thread between each macaroni would be the Ranvier nodules.
This distinct structure of axons means that information does not have to pass through all regions of the axon to reach the nucleus of the cell. Rather, it can travel by saltatory transmission through Ranvier’s nodes.
That is, the nerve impulse travels along 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 much faster and more efficient neural connection and exchange of information.
References
Carlson, N.R. (2011). Behavioral physiology. Madrid: Addison-Wesley Iberoamerican Spain.
Del Abril, A., Caminero, AA, Ambrosio, E., García, C. de Blas MR, de Pablo, J. (2009). Fundamentals of Psychobiology. Madrid. Sanz and Torres.
Kalat, JW (2004). Biological Psychology. Madrid: Thomson Auditorium.