Glial cells are essential for the functioning of the nervous system as they provide structure, nutrients and protection for neurons, as well as to perform other relevant tasks.
In this article we will talk about astrocytes, one of the most common types of glia. We will describe its morphology and its main functions and differentiate the three types of astrocytes that have been identified.
What are astrocytes?
Astrocytes are a type of glial cell located in the central nervous system, That is, in the brain and spinal cord. Like the rest of the glia, astrocytes play supporting roles for neurons, the main cells of the nervous system from a functional point of view.
These glial cells have a shape slightly reminiscent of a star; its name derives from this fact, as the Greek and Latin words “astron” and “astrum” translate to “star” or “celestial body”. Such a structure is due to the fact that they have many extensions (“feet”) that connect the soma to other neighboring cells.
astrocytes they are made up of ectodermal cells, The layer of the embryonic disc from which the nervous system and the epidermis originate, during the early development of the organism. Like most glia, astrocytes start from undifferentiated cells similar to those that give rise to neurons.
Glial cells or glia
As we know, neurons specialize in transmitting nerve impulses. This is why they are very effective at this task, but they need the support of other types of cells for the nervous system to function; it is here that the glia or neuroglía intervene, that is to say the whole of the glial cells, which supposes 50% of the nerve mass.
The specific roles of these cells depend on the type of glia we are referring to. In general, we can say that they mainly serve to provide physical and structural support to neurons, Isolate from each other, supply them with nutrients and oxygen, and remove wastes and pathogens.
Other particularly relevant glial cells are microglia, which perform defensive and immunological functions in the brain and spinal cord, oligodendrocytes and Schwann cells, Which form the myelin sheaths that surround axons and accelerate neuronal transmission to the central and peripheral nervous systems, respectively.
Functions of astrocytes
It was long believed that the function of astrocytes was essentially structural: “filling in the gaps” left by neurons of the nervous system.
However, research in recent decades has shown that their role, like that of other glial cells, is much more complex.
1. Nerve structure
Astrocytes and glia generally play the important role of provide physical support to neurons, So that they stay where they are, in addition to regulating the transmission of electrical impulses. Astrocytes are the most abundant glia in the brain, so their structural role is particularly important in this organ.
2. Blood brain barrier
These glial cells act as intermediaries between neurons and the circulatory system, Specifically the blood vessels. In this sense, they perform a filtering function, so that they are part of the blood-brain barrier, formed by closely related brain endothelial cells.
3. Contribution of nutrients
The connection of astrocytes to the vascular system allows them to obtain nutrients, such as glucose or lactic acid, from the blood and can supply them to neurons.
4.phagocytosis and waste disposal
Likewise, astrocytes collect waste products from neurons and they carry them in the blood so that they can be eliminated. In addition, when an injury occurs in the nervous system, astrocytes move towards it to phagocytize or eliminate dead neurons, forming scars on the damaged area when they accumulate there.
5. Glycogen reserve
It is possible that the astroglia also has the function of storing glycogen, which serves as a reservoir of energy, so that neurons can access these reserves when needed.
6. Regulation of extracellular space
Astrocytes help maintain ionic balance in the extracellular space; in particular, they reverse the excessive accumulation of potassium because they are highly permeable to these molecules.
There are three types of astrocytes that are differentiated by the cell line they come from, that is, the type of neuroepithelial cells they come from. like that, we can distinguish fibrous, protoplasmic and radial astrocytes.
These astrocytes are located in the white matter of the nervous system, that is to say in areas formed mainly by myelinated axons. They are characterized by their low number of organelles (cellular subunits with differentiated functions).
Protoplasmics contain many organelles and they are the most numerous type of astrocyte. They are located mainly in the gray matter of the brain, which is mainly made up of cell bodies.
Radial glia plays a key role during the cell migration process, as neurons “travel” through the nervous system relying on this type of astrocyte. However, there are also radial glial cells that are active in adulthood, such as Bergmann cells located in the cerebellum.
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