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What are Glial Cells?

Meaning of Glial Cells

Glial cells are part of the nervous system. They are auxiliary cells that have the function of supporting the functioning of the central nervous system (CNS). It is estimated that there are 10 glial cells in the CNS for each neuron, but due to their small size they occupy half the volume of nervous tissue.

They differ in form and function and are: oligodendrocytes, astrocytes, Schwann cells, ependymal cells and microglia.

Oligodendrocytes

These cells are responsible for the production of the myelin sheath and serve as an electrical insulator for the neurons of the CNS. They have extensions that wrap around the axons, producing the myelin sheath.

astrocytes

They are star-shaped cells with various processes radiating from the cell body. They present bundles of intermediate filaments made up of glial acid fibrillar protein, which reinforce the cellular structure.

These cells connect the neurons with the blood capillaries and the pia mater. There are fibrous astrocytes and protoplasmic astrocytes.

The former is found in the white matter and the latter is found in the gray matter, having a greater number of extensions that are shorter and extremely branched.

Astrocytes are also involved in the control of the ionic and molecular composition of the extracellular environment of neurons. Some of these cells have extensions called vascular feet, which extend above the blood capillaries.

It is likely that this structure transfers molecules and ions from the blood to the neurons.

These cells are also involved in the regulation of various neuronal activities. They can influence the activity and survival of neurons, due to their ability to control components of the extracellular environment, absorb localized excesses of neurotransmitters, and synthesize neuroactive molecules.

Through gap junctions, astrocytes communicate through gap junctions, forming a network through which information is transmitted, causing them to reach great distances within the CNS.

Schwann cells

They have the same function as oligodendrocytes, however, they are located around the axons of the peripheral nervous system. Each of these cells forms a myelin sheath around a segment of a single axon.
ependymal cells

They are columnar epithelial cells that line the ventricles of the brain and the central canal of the spinal cord. In some regions, these cells are hairy, facilitating the movement of cerebrospinal fluid.

microglia

These cells are small and elongated, with short, irregular extensions. They are phagocytic and are derived from precursors that reach the bone marrow through the bloodstream, representing the mononuclear phagocytic system of the CNS.

They are also involved in CNS inflammation and repair; They also secrete various cytokines that regulate the immune process and remove cellular debris that appear in CNS lesions.

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