Oligodendrocytes: what are they, types and functions of these cells?

Glial cells are the most numerous cells in the human brain, and this is one of their types.

Neurons are essential for the transmission of electrochemical impulses through the nervous system. However, they cannot fulfill this role by themselves: they require the support of glial cells for very different tasks, such as the supply of nutrients, the maintenance of the structure or the acceleration of neuronal conduction itself.

Oligodendrocytes, a type of glial cell that forms the myelin sheaths that wrap the axons of the central nervous system, are particularly important in this last function. In this article we will discuss what oligodendrocytes are and what functions they perform, and we will and describe their two main types.

What are oligodendrocytes?

Oligodendrocytes are a type of glial cell found exclusively in the central nervous system, i.e. in the brain and spinal cord. These cells create myelin sheaths around the axons of neurons, insulating them and increasing their speed.These cells create myelin sheaths around the axons of the neurons, insulating them and increasing the speed of transmission of the electrochemical impulses that travel along them.

In some axons the myelin sheaths are separated into sections; the unmyelinated spaces are called "nodes of Ranvier".. These points allow the jumping conduction of neural impulses: at the nodes of Ranvier, ionic exchanges with the extracellular space regenerate action potentials, further accelerating transmission.

Myelination begins to occur before birth but continues during the first three decades of life. Unlike Schwann cells, which have similar functions in the peripheral nervous system, oligodendrocytes can cover up to 50 different axons thanks to their multiple extensions.

This type of glia is formed in the ventral ventricular region of the spinal cord during intrauterine development, more 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 early neurogenesis.

Glial cells or glia

Glial cells make up half of the nervous system. They perform support functions in relation to neurons.glial cells: they give structure to neuronal networks, nourish them, maintain the stability of the extracellular medium, regulate the growth of dendrites and axons, repair cellular lesions, direct neuronal migration during embryonic development...

Among the most numerous glial cells we find astrocytes, which give structure to the blood-brain barrier (allowing the supply of nutrients and the cleaning of wastes in the nervous system), microglia, which perform immune and regenerative functions, and lSchwann cells, responsible for myelin formation in the peripheral nervous system. in the peripheral nervous system.

The group composed of oligodendrocytes and astrocytes, which are also located in the central nervous system, is called "macroglia" because of the remarkable size of these two cell types in comparison with the rest of glia, especially microglia.

Oligodendrocyte types

The following have been found two main types of oligodendrocytes: interfascicular and satellite oligodendrocytes.. These two subclasses of glial cell differ mainly in their functions, although they are very similar at the structural and molecular level.

Interfascicular oligodendrocytes, which form part of the white matter of the brain and give it its characteristic color, are the basic type; when we speak of "oligodendrocytes" we are usually referring to them, since they are the cells that are responsible for the formation of myelin sheaths, the main role attributed to oligodendrocytes.

In contrast, satellite oligodendrocytes are included in the gray matter because they are not involved in myelin sheath formation. because they are not involved in myelination. They also do not adhere to neurons, so they do not play an isolating role. The exact functions of these oligodendrocytes are not known at this time.

Functions of these cells

In this section we will focus on describing the main roles of interfascicular oligodendrocytes which, as we have said, are better known than those of satellite ones. These roles are mainly associated with the formation of myelin sheaths..

1. Acceleration of neuronal transmission

Myelinated axons send action potentials at a much higher rate than unmyelinated axons, especially if they contain nodes of Ranvier. An adequate rate of neural conduction allows the correct functioning of the muscular and hormonal systems, among other organismic functions, and has also been related to intelligence.

• Related article, "What is neuronal depolarization and how does it work?"

2. Isolation of cell membranes

Myelin sheaths also insulate neuronal axons from the extracellular milieu; this function prevents the leakage of ions from the cell membranes. prevents leakage of ions across the cell membrane..

3. Structuring of the nervous system

Glial cells in general play an important role in maintaining the structure of neuronal networks. These cells are not very robust by themselves, so they need the physical support of glia, including oligodendrocytes.

4. Supporting the development of neurons

Oligodendrocytes produce a variety of neurotrophic factorsproteins that, when interacting with neurons, help them to remain active, preventing apoptosis or programmed cell death. They also promote the cell differentiation required for the formation of neurons.

5. Extracellular fluid homeostasis

It is known that satellite oligodendrocytes do not play the same roles as interfascicular oligodendrocytes because they do not form myelin sheaths. However, they are very relevant for maintaining the homeostatic equilibrium of the extracellular milieu. of the neurons next to which they are located; in contrast to the interfascicular ones, the satellite ones do not bind to these neurons.