Oligodendrocytes, also known as oligodendroglia, are a type of brain cell in the central nervous system that belongs to the glial cell family. The main purpose of glial cells is maintenance and support of nervous system cells. Oligodendrocytes support neurons by producing a substance called myelin, which is composed of approximately 80 percent lipid and 20 percent protein. Essentially, oligodendrocytes wrap the fatty myelin around the nerve-transmitting extensions of nerve cells, which are called axons. These myelin sheaths are approximately .039 inches (about 1 mm) thick, and this sheath acts as insulation for axons – this results in the fast conduction of nerve impulses along axons.
Schwann cells are another type of glial cell that similarly functions to supply myelination to axons. There are, however, several crucial differences between Schwann cells and oligodendrocytes. First, Schwann cells myelinate neurons in the peripheral nervous system, whereas oligodendrocytes myelinate neurons in the central nervous system. Second, a single oligodendrocyte has the capacity to myelinate up to approximately 50 axons, whereas Schwann cells can myelinate only one axon.
Oligodendrocytes arise from oligodendrocyte precursor cells (OPC). In general, a precursor cell is a type of partially differentiated cell that retains the ability to differentiate into several functionally related cell types, but has lost the ability to differentiate into multiple cell types. Small populations of OPCs remain in adults, and OPCs are thought to compose approximately 5 to 10 percent of the adult glial cell population. In response to certain mechanical injuries or viral infections, it is believed that these OPCs are stimulated to grow and replace damaged oligodendrocytes in healthy individuals, resulting in remyelination of neurons.
The myelin sheaths can be compared to the insulation on electrical wires, preventing leakage of ions and maintaining the electrical potential of axons. Therefore, a myelinated axon is much more efficient at transducing signal than an unmyelinated axon. There are several pathological conditions associated with the demyelination of axons, the most common of which is multiple sclerosis (MS).
MS is an autoimmune disease in which the immune system attacks and damages the myelin sheath, resulting in faulty transduction of nerve signals along axons. Leukodystrophies arise from insufficient myelin production during growth, resulting in a variety of symptoms that include the slowing of mental and physical development, progressive loss of movement, and progressive deterioration of senses, such as vision and hearing. Other conditions associated with damage to oligodendrocytes include cerebral palsy, the disabilities resulting from a stroke, and paralysis caused by spinal cord injury.