The main function of the myelin sheath in the nervous system is to insulate axons and enhance the speed of electrical signal transmission. Composed of lipid-rich layers, it allows for saltatory conduction, where impulses jump between gaps (Nodes of Ranvier), leading to faster communication between neurons. This efficient signal propagation is essential for quick reflexes and overall nervous system function. Damage to the myelin sheath, as seen in conditions like multiple sclerosis, can severely disrupt neural communication, highlighting its importance in maintaining neurological health.