Anatomy & Organs

Glial cells – structure, function & diseases

Gliazellen

Glial cells are located in the nervous system and are structurally and functionally distinct from nerve cells . According to recent findings, they play an important role in information processing in the brain and in the entire nervous system. Many neurological diseases are due to pathological changes in glial cells.

What are glial cells?

In addition to nerve cells, glial cells are involved in the structure of the nervous system. They embody many different cell types that are structurally and functionally distinct from one another. Rudolf Virchow, the discoverer of glial cells, saw them as a kind of glue to hold nerve cells together in nerve tissue. He therefore gave them the name glial cells, the root word “glia” being derived from the Greek word “gliokytoi” for glue.

Until recently, their importance for the functioning of the nervous system was underestimated. According to recent research results, however, the glial cells are very active in information processing. Humans have about ten times more glial cells than nerve cells. It has even turned out that the ratio of glial cells to nerve cells is decisive for the speed of nerve stimulus transmission and thus also the thought processes. The more glial cells there are, the faster the information processing.

Anatomy & Structure

Glial cells can be roughly divided into three functionally and structurally distinct cell types. The so-called astrocytes form the main part of the brain . About 80 percent of the brain consists of astrocytes. These cells have a star-shaped structure and are preferably located at the contact points ( synapses ) of the nerve cells.Another group of glial cells are the oligodendrocytes . They surround the axons (nerve processes) that connect the individual nerve cells (neurons) with each other. Astrocytes and oligodendrocytes are also referred to as macroglial cells. In addition to the macroglial cells, there are also the microglial cells. They are everywhere in the brain. While the macroglial cells have their origin in the ectodermal germ layer (outer layer of the embryoblast), the microglial cells originate from the mesoderm. The so-called Schwann cells play a role in the peripheral nervous system .

Schwann cells are also of ectodermal origin and fulfill similar functions as the oligodendrocytes in the brain. Here, too, they surround and supply the axons. There are also some special forms. The so-called Müllerian support cells are the astrocytes of the retina . There are also pituicytes, which represent the glial cells of the posterior pituitary gland . The HHL is made up of 25-30 percent pituicytes. Their function has not yet been fully clarified.

Function & Tasks

Overall, the glial cells fulfill a variety of functions. The astrocytes or astroglia represent the majority of the glial cells present in the nervous system. They are significantly involved in the fluid regulation in the brain. They also ensure that the potassium balance is maintained . The potassium ions released during stimulus transmission are taken up by the astrocytes, while at the same time regulating the extracellular pH balance in the brain.

Astrocytes are of particular importance when participating in cerebral information processing. They contain the neurotransmitter glutamate in their vesicles , which when released leads to the activation of neighboring neurons. The astrocytes ensure that the signals travel long distances in the body and are processed for other neurons at the same time. They differentiate the meaning of individual pieces of information. In addition to moderating the information, they also determine where it should be forwarded. They are therefore responsible for the permanent construction and restructuring of the information network in the brain. Without astrocytes, the transmission of information would be very laborious.

The learning process and thus the formation of intelligence is only possible through the complex cooperation of astrocytes and neurons. The oligodendrocytes, in turn, form the myelin around the nerve cords. The stronger certain strands of information are expanded, the thicker the nerve strands become and the more myelin is needed. The third type of glial cells, the microglial cells, react to pathogens, toxins and dead endogenous cells in the brain in a similar way to the macrophages of the immune system . There are no antibodies through the blood-brain barriercan get into the brain, this task is taken over by the microglial cells. The microglial cells are divided into resting and active cells.

The dormant cells monitor what is happening in their environment. In the event of disturbances caused by injuries or infections , they become freely mobile, migrate to the appropriate place like amoebas and begin their defense and clean-up function. Overall, it is becoming increasingly clear that glial cells not only have supporting functions, but are also largely responsible for the performance of the brain and nervous system.

Diseases

In this context, there is growing awareness of the importance of glial cells for health. Striking changes within the glial cells are observed in many neurological diseases. For example, schizophrenia often breaks out in adolescence, when not all axons are covered with myelin.Very few oligodendrocytes, which are responsible for the formation of myelin, are detected in the corresponding patients. It is possible that some genes that are important for the formation of myelin have also been altered. In multiple sclerosis , the myelin sheath is often destroyed. The exposed nerve extensions can no longer transmit signals and the severed neurons die.

Hereditary leukodystrophy is progressive destruction of the white matter of the nervous system. The myelin surrounding the nerves is broken down. The result is a massive impairment of the nerves. The affected persons suffer from motor and other neurological disorders. Finally, some brain tumors originate in the uncontrolled growth of glial cells.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.