Astrocytes: what functions do these glial cells fulfill?

Glial cells are essential for the functioning of the nervous system as 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 its main functions and we will differentiate the three types of astrocytes that have been identified.

• Related article: "Glial cells: much more than the glue of neurons"

What are astrocytes?

Astrocytes are a type of glial cell located in the central nervous system, that is, in the brain and in the spinal cord. Like the rest of the glia, astrocytes play supporting roles in relation to neurons, the main cells of the nervous system from a functional point of view.

These glial cells are shaped slightly reminiscent of a star.; its name is derived from this fact, since the Greek and Latin words "astron" and "astrum" are translated as "star" or "celestial body". This structure is due to the fact that they have many processes ("feet") that connect the soma with other nearby cells.

Astrocytes are formed from cells of the ectoderm, the layer of the embryonic disc from which the nervous system and epidermis arise, during the early development of the organism. Like most of the 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. For this reason, they are very effective in this task, but they need the support of other types of cells so that the nervous system can function properly; it is here where the glia or neuroglia intervenes, that is, the set of glial cells, which accounts for 50% of the nerve mass.

The specific roles of these cells depend on the type of glia to which we refer. In general we can say that they mainly serve to give physical and structural support to neurons, to isolate each other, to provide them with nutrients and oxygen and to eliminate waste products and pathogens.

Other especially relevant glial cells are the microglia, which performs 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.

• Related article: "Types of neurons: characteristics and functions"

Astrocyte functions

For a long time it was believed that the function of astrocytes was basically structural: "filling in the gaps" left by neurons in the nervous system.

However, research in recent decades has shown that its role, like that of other glial cells, is much more complex.

1. Nervous 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.

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 constitute a part of the blood-brain barrier, made up of closely linked brain endothelial cells.

• You may be interested: "Blood-brain barrier: the protective layer of the brain"

3. Nutrient supply

The connection of astrocytes with the vascular system allows them to obtain nutrients, such as glucose or lactic acid, from the blood and can provide them to neurons.

4. Phagocytization and debris removal

Similarly, astrocytes pick up the waste products of neurons and transport them to the blood so that they can be eliminated. In addition, when an injury occurs in the nervous system, astrocytes move towards it to engulf or remove dead neurons, forming scars in the damaged area by accumulating in is.

5. Glycogen reserve

It is possible that the astroglia also have the function of storing glycogen, which serves as a reservoir energy, with the aim that neurons can access these reserves in moments 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.

Astrocyte types

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. A) Yes, 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 the areas formed predominantly by myelinated axons. They are characterized by their low number of organelles (cellular subunits with differentiated functions).

2. Protoplasmics

Protoplasmatics 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. Radial

The radial glia plays a decisive role during the cell migration process, since neurons "travel" through the nervous system relying on this type of astrocyte. However, radial glial cells are also active in adulthood, such as Bergmann cells located in the cerebellum.

Bibliographic references:

• Aragona M, Kotzalidis GD, Puzella A. (2013). The many faces of empathy, between phenomenology and neuroscience.
• D'Amicis, F., Hofer, P. and Rockenhaus, F. (2011). The automatic brain: the magic of the unconscious.
• Finger, Stanley (2001). Origins of Neuroscience: A History of Explorations into Brain Function (3rd ed.). New York: Oxford University Press, USA.
• Kandel ER; Schwartz JH; Jessel TM (2000). Principles of Neural Science (4th ed.). New York: McGraw-Hill.
• Mohamed W (2008). "The Edwin Smith Surgical Papyrus: Neuroscience in Ancient Egypt". IBRO History of Neuroscience.