The correct answer is the myelin sheath.
Myelin sheath refers to a fatty layering, which produces a protective sheath around the nerve fibers and drastically enhances the rate of transmission of nerve signals. The myelin sheath has various functions in the nervous system.
However, the prime function of it is to safeguard the nerves from other electrical impulses, and accelerating the time it consumes for a nerve to cross an axon.