In unmyelinated axons, the action potential (nerve impulse) travels continuously along the axons and thus, the conduction of nerve impulse is slower. The loss of myelin sheath is called demyelination and is the hallmark of some neurodegenerative autoimmune diseases like multiple sclerosis or acute disseminated encephalomyelitis. Demyelination interrupts signals between the brain and other parts of the body and it includes symptoms like loss of vision/hearing, blurriness in the central visual field, double vision, weakness..
