The glial cell. Functions and features of glial cells

The nervous system consists not only of neurons and their processes. At 40% it is represented by glial cells, which play an important role in its life. They literally restrict the brain and nervous system from the rest of the body's environment and ensure its autonomous work, which is really important for humans and other animals with a central nervous system. And the cells of the neuroglia are able to divide, which distinguishes them from neurons.

General concept of neuroglia

The aggregate of glial cells is called neuroglia. These are special cell populations that are located in the central nervous system and on the periphery. They support the shape of the brain and spinal cord, as well as supply it with nutrients. It is known that in the central nervous system, because of the presence of a blood-brain barrier, there are no immune reactions. However, when a foreign antigen enters the brain or spinal cord, as well as into the cerebrospinal fluid, the glial cell, a reduced analog of the macrophage of peripheral tissues, phagocytizes it. Moreover, it is the separation of the brain from the peripheral tissues that provides neuroglia.

Immune protection of the brain

The brain, where a lot of biochemical reactions take place, which means that a lot of immunogenic substances are formed, should be protected from humoral immunity. It is important to understand that the neuronal tissue of the brain is very sensitive to damage, after which the neurons are only partially restored. Hence, the appearance of a place in the central nervous system, where the local immune response will pass, will cause the death of some surrounding cells or demyelination of the neuron outgrowths.

On the periphery of the body, this damage to somatic cells will soon be filled with newly educated ones. And in the brain it is impossible to restore the function of the lost neuron. And it is the neuroglia that limits the brain from contact with the immune system, for which the central nervous system is a huge amount of foreign antigens.

Classification of glial cells

Glial cells are divided into two types depending on morphology and origin. Isolate microglial cells and macroglia. The first kind of cells originates from the mesodermal leaf. These are small cells with numerous processes, capable of phagocytizing solids. Macroglia is a derivative of the ectoderm. The glial cell of macroglia is divided into several species depending on the morphology. Ependymal and astrocytic cells, as well as oligodendrocytes, are distinguished. Such types of cellular populations are also divided into several types.

Ependymal glial cell

Ependymal glial cells occur in specific areas of the central nervous system. They form the endothelial lining of the cerebral ventricles and the central spinal canal. Their origin in embryogenesis, they take from the ectoderm, and therefore represent a special kind of neuroepithelium. It is multi-layered and performs a number of functions:

• Support: it forms the mechanical framework of the ventricles, which is also maintained by the hydrostatic pressure of the cerebrospinal fluid;
• Secretory: secretes into the liquor some chemicals;
• Delimiting: separates the brain substance from the cerebrospinal fluid.

Types of ependymocytes

Among the ependymocytes there are also their own species. These are ependymocytes of the 1 st and 2 nd order, as well as the tannicites. The first form an initial (basal) layer of the ependymal membrane, and the ependymocytes lie in a second layer above them. It is important that the ependymal glial cell of the 1st order participates in the formation of the hematopoietic barrier (between the blood and the internal environment of the ventricles). Ependymocytes of the second order have villi oriented toward the flow of the cerebrospinal fluid. There are also tannicles that are receptor cells.

They are located in the lateral sections of the bottom of the third cerebral ventricle. Having microvilli on the apical side and one outgrowth on the basal, they can transmit information to neurons about the composition of the liquor fluid. In this case, the cerebrospinal fluid through the small numerous slit-like openings between ependymocytes of the 1st and 2nd order can directly go to the neurons. This allows us to say that ependyma is a special kind of epithelium. Its functional, but not morphological analogue on the periphery of the body is the endothelium of the blood vessels.

Oligodendrocytes

Oligodendrocytes are types of glial cells that surround the neuron and its processes. They occur both in the central nervous system, and near to peripheral mixed and autonomic nerves. The oligodendrocytes themselves are polygonal cells equipped with 1-5 sprouts. They are linked to each other, isolating the neuron from the internal environment of the organism and providing the conditions for nerve conduction and generation of impulses. There are three types of oligodendrocytes, which differ in morphology:

• A central cell located near the body of the brain neuron;
• A satellite cell surrounding the body of the neuron in the peripheral ganglion;
• Schwann cell, covering the neuronal process and forming its myelin sheath.

Oligodendrocyte glial cells are found both in the brain and spinal cord, and in the peripheral nerves. And while it is not known, how does the satellite cell differ from the central one. Given that the genetic material in all cells of the body, except for the sex, the same, it is likely that these oligodendrocytes can mutually replace each other. The functions of oligodendrocytes are as follows:

• Supporting;
• Insulating;
• Separating;
• Trophic.

Astrocytes

Astrocytes are the glial cells of the brain that make up the brain substance. They have a stellate shape and are small in size, although they are larger than microglia cells. There are only two types of astrocytes: fibrous and protoplasmic. The first kind of cells is located in the white and gray matter of the brain, although they are much larger in white.

This means that they are most common in those areas where there is a significant number of neuronal myelinated shoots. Protoplasmic astrocytes are also glial cells: they are found in the white and gray matter of the brain, but they are much larger in gray. Hence, their function is to create a support for the bodies of neurons and the structural organization of the blood-brain barrier.

Microglia

Microglial cells are the last kind of neuroglia. However, unlike all other cells of the central nervous system, they have a mesodermal origin and are special types of monocytes. Their predecessors are stem cells. Due to the peculiarities of the structure of neurons and their outgrowths, glial cells are responsible for immune reactions in the central nervous system. And their functions are almost similar to those of tissue macrophages. They are responsible for phagocytosis and recognition and presentation of the antigen.

Microglia contains special types of glial cells that have receptors of differentiation clusters, which confirms their bone marrow origin and the realization of immune functions in the central nervous system. They are also responsible for the development of demyelinating diseases, Alzheimer's disease and Parkinson's syndrome. However, the cell itself is only a way of realizing the pathological process. Therefore, probably, when it will be possible to find a mechanism of activation of microglia, the processes of development of these diseases will be stopped.