Oligodendrocytes

The Oligodendrocytes belong to the group of glial cells and, along with astrocytes and neurons, are an integral part of the central nervous system. As glial cells, they perform supporting functions for the nerve cells. Some neurological diseases, such as multiple sclerosis, are caused by malfunction of oligodendrocytes.

What are oligodendrocytes?

Oligodendrocytes are a special form of glial cells. In the central nervous system, they are responsible for the formation of myelin sheaths to isolate the nerve processes (axons). In the past, they were mainly assigned support functions similar to connective tissue.

In contrast to connective tissue, however, the oligodendrocytes develop from the ectoderm. Today it is known that they have a great influence on the speed of information processing and on the energetic supply of neurons. In the peripheral nervous system, the Schwann cells take on similar functions as the oligodendrocytes in the CNS.

Oligodendrocytes are mainly found in the white matter. The white matter is made up of axons surrounded by a myelin sheath. The myelin gives this region of the brain its white color. In contrast, gray matter is made up of the cell nuclei of neurons. Since there are fewer axons here, the number of oligodendrocytes in the gray matter is also limited.

Anatomy & structure

Oligodendrocytes are cells with small, round cell nuclei. Your cell nuclei have a high content of heterochromatin, which can be easily detected by various staining techniques. Heterochromatin ensures that the genetic information in the oligodendrocytes usually remains inactive. In this way, the stability of these cells should be preserved so that they can perform their support function undisturbed.

Oligodendrocytes have cell processes that produce myelin. With their appendages they envelop the axons of the nerve cells and thereby form myelin. With this myelin they wrap the nerve processes in a spiral. An insulating layer forms around the individual axons. One oligodendrocyte can produce up to 40 myelin sheaths that wrap several axons. The oligodendrocytes, however, have fewer processes than the other glial cells in the brain, the astrocytes.

The myelin consists mainly of fats and to a lesser extent of certain proteins. It is impermeable to electrical currents and therefore acts like a strong insulating layer. In this way the individual axons are separated from one another. This layer of insulation looks similar to insulation around a cable. The insulating layer is missing at intervals of 0.2 to 1.5 millimeters.

These areas are known as Ranvier lacings. Both the isolation and the formation of isolated sections have a great influence on the speed of information transmission.

Function & tasks

The oligodendrocytes effectively isolate the individual nerve cell processes from one another with their myelin sheaths. In addition, there are short, uninsulated areas of the myelin sheath at certain intervals, which are known as Ranvier's laced rings. In this way, the nerve signals can be transmitted more effectively and faster.

The isolation of the axons accelerates signal transmission. Dividing the insulation into sections makes this acceleration even more effective. The signal jumps from ring to ring. In this way, a speed of up to 200 meters per second or 720 km per hour can be generated. It is this high speed that enables highly complex information processing to develop. The same applies to the separate transmission through the isolation of the nerve cords. Without the myelin sheaths, the axons would have to be very thick to achieve high signal speeds.

It has already been calculated that our optic nerve alone, without myelin sheaths, would have to be as thick as a tree trunk in order to perform as well. In such complex organisms as vertebrates and especially humans, innumerable nerve impulses are transmitted, which have to be prepared for information processing. Without oligodendrocytes, complex information processing and thus the development of intelligence would not be possible at all.

This function of oligodendrocytes has been known for decades. In recent years, however, there has been increasing awareness that oligodendrocytes perform even more functions. For example, the axons are very long and the transmission of the signal also costs energy. However, the energy within the axons is insufficient, especially since there is no replenishment from the cytoplasm of the neuron. According to the latest findings, the oligodendrocytes also take up glucose and even store it as glucogen.

When there is an increased energy requirement in the axons, the glucose is first converted to lactic acid in the oligodendrocytes. The lactic acid molecules then migrate through channels in the myelin sheath into the axon, where they supply energy for signal transmission.

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Diseases

Oligodendrocytes play a major role in the development of neurological diseases such as multiple sclerosis. In multiple sclerosis, the myelin sheaths are destroyed and the isolation of the axons is lost. The signals can no longer be passed on correctly.

It is an autoimmune disease in which the immune system attacks and destroys the body's own oligodendrocytes. Multiple sclerosis often comes on in flares. After each attack, the body is stimulated again to produce new oligodendrocytes. The disease calms down. If the inflammation and thus the destruction of the oligodendrocytes becomes chronic, the nerve cells also die. Since these cannot regenerate, permanent damage occurs.

The question remains, however, why the neurons also perish. The discoveries made in recent years provide an answer. Oligodendrocytes supply the neurons with energy via the axons. When the energy supply ends, the nerve cells also die.