The function of the myelin sheath is to facilitate the conduction of electrical impulses through the nerve cells. The myelin sheath is made out of a modified plasma membrane that is wrapped around the nerve axon in a spiral pattern.
The myelin sheath is essential for the proper functioning of the nervous system. When the myelin is damaged, nerve impulses slow down, and the nerve cell begins to wither. Diseases such as multiple sclerosis can result from damaged myelin sheaths. The sheath increases the electrical resistance of the cell by a factor of 5,000, which prevents the electrical current from leaving the axon of the nerve cell. The process of forming the myelin sheath is known as mylenization. The production of myelin begins during the 14th week of fetal development, but very little myelin is found in the brain at birth.
During infancy, mylenization occurs at a rapid rate and continues until adolescence. The myelin sheath is made up of lipids and proteins, and lipids account for 70 to 80 percent of the sheath's structure. Accordingly, it is important that infants receive greater amounts of fat in their diet than their adult counterparts. Myelin was originally discovered in 1854 by Rudolf Virchow, a German doctor.