Glial cells are essential for the proper functioning of the human nervous system. There are different types of glial cells, and each of them has different functions - some glial cells are responsible for the elimination of unnecessary, used cells, others produce the myelin sheath, and still others are involved in the nutrition of neurons.
Glial cells , otherwiseglej(Greek glial cells) are the cells of the human nervous system that enable action of nerve cells (neurons).
The name of glial cells is derived from the Greek word glia, which means glue, and it was initially indeed suspected that the main function of these glial cells was to bind nerve cells together. Years later, it turned out that the reality was somewhat different, but it became known a long time after the existence of glial cells in the nervous system was first discovered.
Glial cells: history, definition
The pathologist Rudolf Virchow, who was looking for some kind of connective tissue in the brain, and who finally made the first description of the glia, is credited with the discoverer of glial cells. It was published in 1856, but the researcher was still interested in these cells and two years later, in 1858, he provided a much more detailed description of them.
Many different studies have already been carried out on glial cells, thanks to which more and more has been learned about them - scientists have already managed to find out, for example, that the belief that glial cells can be even ten times more than nerve cells (nowadays the dominant view is that the ratio of neurons to glial cells is rather 1: 1).
Glial cells: types
Different types of glial cells are found in the central and peripheral nervous systems. In the case of the first of these, there are:
- astrocytes: the most widespread glial cells in the central nervous system, which have numerous projections directed towards nerve cells; astrocytes nourish neurons, and they affect the management of various substances in the central nervous system (this type of glial cells, e.g. removes excess potassium from the vicinity of nerve cells, in addition, astrocytes are involved in the metabolism of neurotransmittersreleased by neurons), they also affect the condition of the blood vessels of the nervous system - astrocytes can secrete mediators leading - depending on the needs - to their contraction or relaxation,
- oligodendrocytes: glial cells responsible for the production of myelin sheaths in the central nervous system (thanks to it, the transmission of impulses between individual neurons occurs much faster than in those fibers that are not covered with myelin),
- ependemocytes (ependymal cells): they can be found within the spinal cord and in the ventricles of the ventricular system of the brain, where they are responsible for the production and secretion of cerebrospinal fluid, in addition, ependemocytes are one of the elements of the blood-brain barrier,
- radial glia: progenitor cells from which various cells belonging to the central nervous system can develop, because both astrocytes and oligodendrocytes, and even nerve cells in special situations.
All the types of glial cells mentioned above are called macroglia. In the central nervous system, however, there are also microglia - this term is used to describe the specialized macrophages residing in the structures of the CNS, whose task - thanks to their ability to phagocytose - is to remove dead cells, but also to eliminate foreign antigens that are found in the central part of the central nervous system. nervous system.
Other glial cells occur within the peripheral nervous system in which they are found:
- Schwann cells: they have a function similar to oligodendrocytes - Schwann cells are responsible for the production of the myelin sheaths of these nerve fibers, which belong to the peripheral nervous system, in addition, they also have the ability to phagocytosis, thanks to which they can remove unnecessary cells and other substances from the vicinity of nerve cells,
- satellite cells: small glial cells that surround the nerve cells that make up the ganglia of the sympathetic, parasympathetic and somatic systems.
Glial cells: functions
We can definitely say that the functioning of nerve cells without the support of glial cells would simply be impossible. After all, it is the glial cells, which include, among others, astrocytes are responsible for supplying neurons with various nutrients necessary for their survival, they are also involved in removing unnecessary metabolites from them.
Glej is responsible for the elimination of unnecessary cells in the nervous system, and it affects the circulation and the removal of various secreted in itneurotransmitters. Glial cells produce myelin sheaths, thanks to which the transmission of impulses in the nervous system is really fast and thanks to this, it takes only tens of seconds from thinking about a given activity to performing it.
During adolescence, glia supports the development of both neurons and synaptic connections, additionally - in the case of damage to the fibers of the peripheral nervous system - Schwann cells belonging to the glia are involved in the regeneration of these structures.
Glial cells: diseases
As it is probably not difficult to guess, abnormalities in the functioning of glial cells can lead to the occurrence of certain diseases in humans. As an example, microglial dysfunction may be associated with diseases such as Alzheimer's disease or fibromyalgia, and it is also suggested that microglia malfunction may have some impact on the incidence of schizophrenia in humans.
Dysfunctions in other glial cells, which are Schwann cells, are associated with conditions such as Guillain-Barre syndrome, Charcot-Marie-Tooth disease, and chronic inflammatory demyelinating polyneuropathy. In humans, there can also be various types of neoplasms that originate from glial cells - their examples include, among others, astrocytomas, gliomas, oligoastomas and ependymomas.