The Nervous System is not only made up of neurons. Together with the neurons, which are the functional unit of the SN, we find the glial cells (glia or glia).
Neuroglia, also called glial cells, are cells of the nervous system. They are part of a support system and are essential for the proper functioning of the nervous system tissue. Unlike neurons, glial cells have no axons, dendrites or nerve conduits. Neuroglia are smaller than neurons and are approximately three times more numerous in the nervous system.
They are also much more abundant than neurons; in the SNC of vertebrates there are ten to fifty times more glial cells than neurons. Glial cells were described around 1850 by Rudolf Virchow (1821 to 1902).
- 1 What are glial cells?
- 2 astrocytes
- 3 Ependymal cells
- 4 Microglia
- 5 Oligodendrocytes
- 6 Astroglia
- 7 Schawnn cells
What are glial cells?
The word glia it means 'tail' in Greek Thus, the term neuroglia I would like to say "neuron adhesive." This name was given by Rudolf Virchow because he thought that these cells served as an adhesive for neurons, which united them to form nerve tissue. Thus, the main function of glial cells would be structural, that is, to provide physical support to neurons.
Glial cells are found around neurons and develop very important functions, such as providing structural and metabolic support to neurons.
The set of glial cells is called neuroglia.
There are several types of glial cells present in the central nervous system (CNS) and the peripheral nervous system (SNP) of the humans. The six main types of neuroglia include the following:
They are the most abundant glial cells and are named in this way by their starry shape.
They are found in the brain and spinal cord. They are star-shaped neuroglia that resides in the endothelial cells of the CNS that form the blood-brain barrier. This barrier restricts which substances can enter the brain. The protoplasmic astrocytes they are found in the gray matter of the cerebral cortex, while the fibrous astrocytes They are found in the white matter of the brain. Other functions of astrocytes include glycogen storage, nutrient provision, ion concentration regulation and neuron repair.
- Nutrient supply to neurons: they act as a link between the circulatory system (where the nutrients that neurons need) and neurons.
- Structural support: are among the neurons and provide physical support to the neurons and consistency in the brain.
- Repair and regeneration: glial cells maintain their ability to divide throughout life (something that neurons cannot do). When a CNS lesion occurs, astrocytes proliferate and emit a number of extensions (these changes are called gliosis). The astrocytes clean the injured area, ingesting and digesting the remains of neurons by phagocytosis. In addition, astrocytes proliferate to "fill the void" left by the lesion. On the other hand, astrocytes could have a very important role in the regeneration of neurons because they release various growth factors.
- Separation and isolation: they act as a barrier between neurons on the diffusion of different substances such as ions or neurotransmitters (astrocytes isolate synapses preventing the dispersion of the neurotransmitter released by the terminal buttons).
- Collection of chemical transmitters: Astrocytes can capture and store neurotransmitters.
Ependymal cells are specialized cells that line the brain ventricles and the central canal of the spinal cord. They are found within the choroid plexus of the meninges. These hair cells surround the choroid plexus capillaries and form cerebrospinal fluid.
They form the epithelial lining of the ventricles of the brain and the central channel of the spinal cord.
Ependymal cells, like other neuroglia cells, are derived from a layer of embryonic tissue known as neuroectoderm.
- Choroidal epithelial cells: cover the surfaces of the choroid plexus. The sides and bases of these cells form folds and near their luminal surface, the cells are held together by the tight junctions that surround them. These tight junctions prevent the filtration of cerebrospinal fluid into the underlying tissues.
- Ependymocytes: cover the ventricles of the brain and the central duct of the spinal cord. They are in contact with the cerebrospinal fluid. Its adjacent surfaces have groove joints but the cerebrospinal fluid communicates freely with the intercellular spaces of the central nervous system.
- Tanicitos: cover the floor of the third ventricle above the middle eminence of the hypothalamus. They have long basal extensions that pass between the cells of the middle eminence and place their terminal basal cells on the blood capillaries.
Functions of ependymal cells
They give rise to the epithelial layer that surrounds the choroid plexus in the lateral ventricles of the Cerebral hemisphere. These epithelial cells produce mainly cerebrospinal fluid.
The ependymal cells have cilia and are located in front of the cavity of the ventricles. The coordinated movement of these cilia influences the direction of cerebrospinal flow, the distribution of neurotransmitters and other messengers for neurons.
Ependymal cells called Tanicites play an important role in the transport of hormones in the brain.
The microglia are extremely small cells of the nervous system centersl that eliminate cellular debris and protect against microorganisms (bacteria, viruses, parasites, etc.). Microglia are thought to be macrophages, a type of white blood cell that protects against foreign matter. They also help reduce inflammation by releasing anti-inflammatory cytokines.
Functions of the microglia
Under normal conditions, the number of microglia cells is small, but when an injury or inflammation of the nervous tissue occurs, these cells proliferate rapidly (as do astrocytes) and migrate to the area of the lesion to phagocyte cell debris, myelin fragments or injured neurons.
The microglia acts as a phagocytic cell and protects the brain from microorganisms invaders
Oligodendrocytes are structures of the central nervous system that involve some neuronal axons to form an insulating layer known as myelin sheath. The myelin sheath, composed of lipids and proteins, functions as an electrical insulator for axons and promotes more efficient conduction of nerve impulses.
Oligodendrocyte An oligodendrocyte can myelinate segments of different axons
They form the myelin layer of the CNS: a single oligodendrocyte can mix different segments of the same axon or of different axons (from 20 to 60 different axons).
An oligodendrocyte surrounds different unmyelinated axons
The oligodendroglia also has a protective function on unmyelinated axons, as it surrounds them and keeps them fixed.
Oligodendroglia forms the myelin sheath in the CNS.
There are autoimmune diseases that destroy the myelin layer: in the multiple sclerosis The cells that form myelin are not recognized by the body as their own and are destroyed. This disease is progressive, and depending on the amount and function of neurons that lose myelin the consequences will be more or less serious.
These satellite glial cells cover and protect the neurons of the peripheral nervous system. They provide structural and metabolic support for sensory, sympathetic and parasympathetic nerves.
In the SNP, each Schawnn cell forms a single myelin segment for a single axon.
In the peripheral nervous system (SNP), Schawnn cells perform the same functions as the different glial cells of the CNS. These functions are as follows:
- Like astrocytes, are located between the neurons.
- Like the microglia, phagocytize the remains in the case of an injury in the peripheral nerves.
- Like oligodendrocytes, one of the main functions of Schawnn cells is form myelin around the axons of the SNP. Each Schawnn cell forms a single myelin segment for a single axon.
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