Antibodies are proteins produced by the immune system.
Normally, antibodies are sent out to fight infection and disease, but sometimes they are mistakenly sent out to attack healthy tissue. In MG, even though there is nothing wrong with the neuromuscular junction, somehow the immune system gets triggered to attack it anyway. The antibodies bind to the muscle's membrane and initiate a series of events that destroy the membrane and prevent ACh from binding. If ACh can't bind to the muscle, the muscle won't contract. MG is sometimes associated with other autoimmune diseases, including rheumatoid arthritis and thymus abnormalities.