Final answer:
In Multiple Sclerosis, myelin breakdown is caused by an autoimmune response where lymphocytes attack the central nervous system's myelin, leading to inflammation and neural scarring.
Step-by-step explanation:
The breakdown of myelin in Multiple Sclerosis (MS) is primarily caused by the body's immune system attacking the myelin in the central nervous system. This autoimmune response involves the production of antibodies by lymphocytes, a type of white blood cell, which mistakenly mark myelin as foreign and initiate its destruction. This leads to inflammation, demyelination, and the subsequent scarring or sclerosis of neural tissue, impairing the electrical signaling required for normal neurological function.