Astrocytes: What Functions Do These Glial Cells Fulfill?
Glial cells are essential for the functioning of the nervous system since they provide structure, nutrients and protection to neurons, in addition to carrying out 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 main functions and differentiate the three types of astrocytes that have been identified.
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 support roles in relation to neurons, the main cells of the nervous system from a functional point of view.
These glial cells have a shape that slightly resembles that of a star ; Its name is derived from this fact, since the Greek and Latin words “astron” and “astrum” translate as “star” or “celestial body.” Such a structure is due to the fact that they have many extensions (“feet”) that connect the soma with other nearby cells.
The astrocytes They are formed from ectoderm cells, the layer of the embryonic disc from which the nervous system and epidermis arise, during the early development of the organism. Like most glia, astrocytes arise from undifferentiated cells similar to those that give rise to neurons.
As we know, neurons specialize in the transmission of nerve impulses. Therefore, they are very effective in this task, but they need the support of other cell types so that the nervous system can function correctly; This is where the glia or neuroglia intervene, that is, the set of glial cells, which makes up 50% of the nervous 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 to isolate one from another, to provide them with nutrients and oxygen and to eliminate waste products and pathogens.
Other especially 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 the axons and accelerate neuronal transmission in the central and peripheral nervous systems, respectively.
Functions of astrocytes
For a long time it was believed that the function of astrocytes was basically structural: “filling the gaps” left by neurons in the nervous system.
However, research in recent decades has shown that its role, like that of the rest of the glial cells, is much more complex.
1. Nerve structure
Astrocytes and glia in general play the important role of provide physical support to neurons, so that they remain in the place 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 especially relevant in this organ.
These glial cells act as intermediaries between neurons and the circulatory system, specifically the blood vessels. In this sense, they fulfill a filtering function, so that they constitute a part of the blood-brain barrier, formed by closely linked brain endothelial cells.
3. Nutrient contribution
The connection of astrocytes with the vascular system allows them to obtain nutrients, such as glucose or lactic acid, from the blood and provide them to neurons.
4. Phagocytation and waste removal
Similarly, astrocytes collect waste products from neurons and They transport them to the blood so they can be eliminated Furthermore, when an injury occurs in the nervous system, astrocytes move towards it to phagocytize or eliminate dead neurons, forming scars in the damaged area by accumulating therein.
5. Glycogen reserve
It is possible that astroglia also have the function of storing glycogen, which serves as an energy store, so that neurons can access these reserves in times of need.
6. Regulation of extracellular space
Astrocytes help maintain ionic balance in the extracellular space; specific, reverse excessive potassium accumulation because they are very permeable to these molecules.
Types of astrocyte
There are three types of astrocytes that are differentiated by the cell lineage from which they come, that is, the type of neuroepithelial cells from which they originate. So, we can distinguish between fibrous, protoplasmic and radial astrocytes
1. Fibrous
These astrocytes are located in the white matter of the nervous system, that is, in areas formed predominantly by myelinated axons. They are characterized by their low number of organelles (cellular subunits with differentiated functions).
Protoplasmic cells contain many organelles and They are the most numerous type of astrocyte They are located mainly in the gray matter of the brain, composed mainly of cell bodies.
3. Radials
Radial glia play a determining role during the cell migration process, since neurons “travel” through the nervous system relying on this type of astrocytes. However, there are also active radial glial cells in adulthood, such as Bergmann cells located in the cerebellum.
