Myelin is a fatty white substance that surrounds the axon of some nerve cells, forming an electrically insulating layer. It is essential for the proper functioning of the nervous system.
The production of the myelin sheath is called myelination or myelinogenesis. During infancy, myelination occurs quickly, leading to a child’s fast development, including crawling and walking in the first year. Myelination continues through the adolescent stage of life.
Schwann cells supply the myelin for the peripheral nervous system, whereas oligodendrocytes, myelinate the axons of the central nervous system. Myelin was discovered in 1854 by Rudolf Virchow.
Cholesterol is an essential constituent of myelin. Myelin is about 40% water; the dry mass is about 70–85% lipids (group of naturally occurring molecules that include fats, waxes, sterols) and about 15–30% proteins.
Myelin is made by different cell types, and varies in chemical composition and configuration, but performs the same insulating function. Myelinated axons are white in appearance, hence the term “white matter” of the brain. Myelin helps to insulate the axons from electrically charged atoms and molecules.
What Does Myelin Do?
The main purpose of a myelin layer (or sheath) is to increase the speed at which impulses propagate along the myelinated fibre. Along unmyelinated fibres, impulses move continuously as waves, but, in myelinated fibres, they “hop” or propagate by saltatory conduction. Myelin also helps prevent the electric current from leaving the axon.
Demyelination is the loss of the myelin sheath insulating the nerves and is the hallmark of some neurodegenerative autoimmune diseases, including multiple sclerosis, acute disseminated encephalomyelitis, neuromyelitis optica, transverse myelitis, chronic inflammatory demyelinating polyneuropathy, Guillain-Barré syndrome as well as others.
Demyelination And Multiple Sclerosis
Multiple sclerosis (MS) is the most common demyelinating disease of the central nervous system. In this disorder, a person’s immune system attacks the myelin sheath or the cells that produce and maintain it.
This causes inflammation and injury to the sheath and ultimately to the nerve fibers that it surrounds and may result in multiple areas of scarring (sclerosis).
Remyelination is the process of propagating oligodendrocyte precursor cells to form oligodendrocytes to create new myelin sheaths on demyelinated axons in the CNS. This is a process naturally regulated in the body and tends to be very efficient in a healthy CNS.
The process creates a thinner myelin sheath than normal, but it helps to protect the axon from further damage, from overall degeneration and proves to increase conductance once again. Demyelinating diseases, such as Multiple Sclerosis, have been of utmost interest within the last couple of decades. Recent research is uncovering some of the many unknown pathways involved with remyelination in hopes of battling demyelinating diseases like MS which can ultimately cripple a person. While no treatment exists yet in preventing remyelination failure in the chronic stages of these diseases, future research may yet prove to unlock key pathways that can be targeted.