Oligodendrocytes: Definition & Function |

Oligodendrocytes – Definition

Until the 20th century, it was assumed that glial cells only have a supporting and protective function in the nervous system. The fact that glial cells, and especially oligodendrocytes, also take on other tasks is explained below.

Figure 1: Origin of oligodendrocytes Source:

Together with astrocytes, oligodendrocytes belong to the macroglia. These have the same origin in terms of development, but differ significantly both in their form and in their functions.

Oligodendrocytes – Appearance

The nuclei of the oligodendrocytes are small and round. They have a high proportion of heterochromatin. Heterochromatin are highly condensed, «packed» chromosomes.

In contrast to astrocytes, oligodendrocytes have only a few cell processes. These are also less branched. Just as you can imagine astrocytes as stars, oligodendrocytes resemble deciduous trees.

Figure 2: Oligodendrocytes (red) in cell culture. Cell nuclei stained blue. Source: mpg.de

The processes of the oligodendrocytes spiral around the axons of the neurons. Oligodendrocytes are mainly found in the white matter of the central nervous system.

Oligodendrocytes – function and tasks

Oligodendrocytes insulate axons

The oligodendrocytes produce myelin. With this they wrap the axons of the neurons. As a result, the nerve tracts are electrically isolated and faster signal transmission can take place.

Myelin is a biomembrane. This is wrapped around the axons. The axons of neurons in both the peripheral and central nervous systems are surrounded by myelin. The oligodendrocytes are responsible for this in the central nervous system and the Schwann cells in the peripheral nervous system.

However, the wrapping of the axons with myelin is not continuous. A bit of space is always left between two sections. One section is called the myelin sheath. Because these «gaps» are so small, it looks under the microscope as if the myelin is just being constricted. Hence the term «Ranvier node rings». However, these are individual cell extensions that are independent of one another. The insulation and the Ranvier stoking rings allow the so-called saltatory conduction.

Figure 3: Schematic representation of an oligodendrocyte (blue) and a neuron (orange) Source: biermann-medizin.de

The advantage of saltatory conduction over continuous conduction is that the action potential does not have to travel the entire distance of the axon. The action potential can «jump» from one node of Ranvier to another. More precisely, it is formed anew at each gap.

The saltatory excitation line enables 100X faster signal transmission compared to the continuous excitation line. So, the wrapping of neurons with oligodendrocytes is the reason for human intelligence.

Oligodendrocytes possess neurotransmitter receptors

Like other nerve cells, oligodendrocytes have receptors for neurotransmitters on their cell surface. The most common receptor is the ionotropic glutamate receptor. As a result, oligodendrocytes, like neurons, can become depolarized.

Oligodendrocytes form glial scars

If nerve tracts in the central nervous system are destroyed, they can only be repaired at great expense. One reason for this are astrocytes and oligodendrocytes. These glial cells release certain growth inhibitors that prevent nerve tracts from regenerating. An injury to the central nervous system also stimulates the division of astrocytes and oligodendrocytes. This leads to the formation of so-called glial scars.

Diseased oligodendrocytes – multiple sclerosis

Oligodendrocytes form myelin and are therefore essential for the rapid transmission of information. In the case of the autoimmune disease multiple sclerosis, the myelin sheaths of the nerve fibers are attacked. Many small foci of inflammation develop.

This leads to the breakdown of myelin. One also speaks of “de-marking”. If the nerve fibers are no longer adequately insulated, it becomes more difficult to transmit information.

Especially in the beginning there are vision problems, numbness and pain. In the further course, paralysis of the extremities or spastic movements can occur.

Figure: Possible locations of multiple sclerosis Source: t-online.de

The causes of multiple sclerosis are not yet known. Likewise, multiple sclerosis cannot be cured. Multiple sclerosis is the second most common neuronal disease in young people.