What are the functions of oligodendrocytes?

Answer: Oligodendrocytes are glial cells that are best known for myelinating axons. They also participate in axonal maintenance, providing sustenance to the neurons.

oligodendrocyte myelin

The brain consists of about 85 billion neurons with an estimated equal number of glial cells. Long regarded as simply support cells with little ability to change or to perform dynamic functions, glial cells have been gaining interest to researchers since the latter half of the 1900s.

Broadly speaking, there are four classes of glia: oligodendrocytes, Schwann cells, microglia, and astrocytes. They all perform some important functions within the nervous system.

Interest in the oligodendrocytes developed around the mid-1900s. Prior to this time, the myelin sheath that surrounds axonal processes to improve signal transduction was believed to be created by the axon itself. Groundbreaking research informed us that glial cells, not neurons, are responsible for this function (Development of the fine structure of the myelin sheath in sciatic nerves of chick embryo). Even though glia such as oligodendrocytes and Schwann cells perform this crucial role in the brain and spinal cord, they were not thought of serving any other function. In fact, the word glia comes from the word for glue.

As the oligodendrocyte matures, it begins branching. It sends processes out from the soma to make contact with axons. Originally it was thought these processes were simple filipodia, but now it is understood that they function more like a growth cone that actively searches for processes to myelinate. Once an appropriate axon is identified, the oligodendrocyte cell membrane expands to ensheath the cell body in layers of fatty membrane. Finally, the cytoplasm from the cell is extruded, and the mature myelin is formed. Each oligodendrocyte is able to myelinate several nearby neurons.

Schwann cells are similar in function to oligodendrocytes. Whereas oligodendrocytes act in the brain and spinal cord, Schwann cells act in the peripheral nervous system, and myelinate axons outside of the brain.

Myelin is best known for its function to allow for proper conduction of action potentials down the axon through a process called saltatory conduction. Dysfunction in myelin can lead to diseases such as multiple sclerosis.

However, myelin also serves an important role in axonal maintenance. Many proteins that are expressed at the surface of the myelin are directly in contact with the axonal membrane, and are essential for axonal survival. In the case of demyelination, axons develop abnormal swellings and consequently degenerate. (Axonal swellings and degeneration in mice lacking the major proteolipid of myelin.) Myelin has also been demonstrated to transport lactate, the molecule that is responsible for generating ATP, the source of cellular energy (The role of myelin and oligodendrocytes in axonal energy metabolism).