Neurons are essential for the transmission of electrochemical impulses through the nervous system. However, they cannot fulfill this role on their own: they require the support of glial cells for very different tasks, such as providing nutrients, maintaining structure, or accelerating neural conduction itself. .
In the latter function, oligodendrocytes, a type of glial cell that forms the myelin sheaths that surround axons of the central nervous system, are particularly important. In this article we will analyze what oligodendrocytes are and what functions they perform and we will describe its two main types.
What are oligodendrocytes?
Oligodendrocytes are a type of glial cell that is found exclusively in the central nervous system, that is, in the brain and spinal cord. These cells create myelin sheaths around the axons of neurons, Isolate them and increase the transmission speed of the electrochemical impulses passing through them.
In some axons, the myelin sheaths are separated into sections; unmyelinated spaces are called “Ranvier’s nodules”. These points allow the jumping conduction of neural impulses: in Ranvier’s nodules, ion exchanges with the extracellular space regenerate action potentials, further accelerating transmission.
Myelination begins to occur before birth but continues for the first three decades of life. Unlike Schwann cells, which perform similar functions in the peripheral nervous system, oligodendrocytes can span around 50 different axons thanks to their multiple extensions.
This type of glia it forms in the ventral ventricular region of the spinal cord during intrauterine development, later than other types of glia. In adults, oligodendrocytes continue to appear from glial progenitor cells, although their number is much lower than that present during the first neurogenesis.
Glial cells or glia
Glial cells make up half of the nervous system. They perform support functions vis-à-vis neurons: They structure neural networks, nourish them, maintain the stability of the extracellular environment, regulate the growth of dendrites and axons, repair cell damage, direct neuronal migration during embryonic development, etc.
Among the most numerous glial cells are the astrocytes, which structure the blood-brain barrier (allowing the supply of nutrients and the cleaning of wastes in the nervous system), the microglia, which performs immune and regenerative functions, andas Schwann cells, responsible for the formation of myelin in the peripheral nervous system.
The set made up of oligodendrocytes and astrocytes, also located in the central nervous system, is called “macroglia” because of the remarkable size of these two types of cells compared to other glia, in particular microglia.
Types of oligodendrocytes
They were found two main types of oligodendrocytes: interfascicular and satellite. These two subclasses of glial cells differ mainly in their functions, although they are very similar structurally and molecularly.
The interfascicular oligodendrocytes, which are part of the white matter of the brain and give it its characteristic color, are the basic type; When we speak of “oligodendrocytes”, the most common is that we refer to them, because these are the cells that take care of the formation of myelin sheaths, the main role being attributed to the oligodendrocytes.
In contrast, satellite oligodendrocytes are included in gray matter because they are not involved in myelination. They also do not adhere to neurons and therefore do not play an insulating role. We do not currently know what the functions of these oligodendrocytes are.
Functions of these cells
In this section we will focus on describing the main roles of interfascicular oligodendrocytes which, as we said, are better known than those of satellites. these functions they are mainly associated with the formation of myelin sheaths.
1. Acceleration of neuronal transmission
Myelinated axons send out action potentials at a much faster rate than those that are not, especially if they contain Ranvier nodules. Adequate rhythm of neural conduction enables proper functioning of the muscular and hormonal systems, among other organ functions, and has also been linked to intelligence.
2. Isolation of cell membranes
Myelin sheaths also isolate neuronal axons from the extracellular environment; this function prevents the filtration of ions through the cell membrane.
3. Structure the nervous system
Glial cells generally play an important role in maintaining the structure of neural networks. These cells are weak on their own, so they need the physical support of the glia, including oligodendrocytes.
4. Support the development of neurons
Oligodendrocytes produce several neurotrophic factorsProteins which, when interacting with neurons, promote their activity, preventing apoptosis or programmed cell death. They also promote cell differentiation necessary for the formation of neurons.
5. Homeostasis of extracellular fluid
It is known that satellite oligodendrocytes do not play the same roles as oligodendrocytes because they do not form a myelin sheath. However, they are very relevant for maintain the homeostatic balance of the extracellular environment neurons next to those located; on the contrary that the interfasciculars, the satellites are not united to these.
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