Myelin is a dielectric material forming an insulating coat around axons and neurons. These coats aid in the accurate transmission of electrical current between nerve cells and are essential for the functioning of the nervous system. Myelin develops from glial cells through myelination, a process which occurs in the fourteenth week of fetal development and continues until adolescence. Until the age of two, the myelination process occurs quickly and requires a higher fat ratio in the diet. The peripheral neurons of the peripheral nervous system (carrying sensory input) are myelinated by Schwann cells, and the central nervous system is myelinated by oligodendrocytes.
Myelin surrounding axons is white and has a lipid protein content of 70 to 80%. The axons from these cells have a different lipid composition. Myelin sheaths have a double function: they protect the electrical signal communicated by neurons against interference and corruption, but also prevent the leakage of energy and speeds up the conduction.
A damaged myelin sheath can result in a reduced speed of communication between neurons, resulting in slow reactions, or mix-ups of sensory signals. The myelin layer can re-grow if severed using an intrinsic mechanism, but this myelin regeneration does not occur properly. Multiple sclerosis is a disease which causes demyelination due to an auto-immune reaction. Typical symptoms include blurriness of vision, odd tingling sensations, weakness, heat sensitivity, disruption of cognitive functions and coordination disorders. In a later stage, the oligodendrocytes producing myelin in the central nervous system are also destroyed so myelin is no longer replaced.