Final answer:
Multiple sclerosis (MS) is a disease characterized by the degeneration of the myelin sheath, affecting signal transmission in neurons and leading to various neurological symptoms.
Step-by-step explanation:
Multiple sclerosis (MS) is most directly associated with the degeneration of the myelin sheath. MS is an inflammatory disease that affects the central nervous system by damaging the myelin sheaths which insulate neurons in the brain and spinal cord. This destruction hinders the neurons' ability to transmit signals properly, leading to a range of symptoms including physical, psychiatric, and cognitive deficits. The disease can progress through isolated attacks or a slower, degenerative progression, with permanent damage over time.