It is an illness that develops when the person's body tissues are attacked by their own immune system. Our immune system is a complex organization within the body which is designed to find and destroy foreign undesirable invaders, such as bacteria, toxins, or viruses. If somebody has an autoimmune disease their abnormal antibodies, which circulate in the blood, attack desirable things (things that should be protected and not destroyed), such as body tissues.

In the case of myasthenia gravis, antibodies are produced that block or destroy muscle receptor cells, resulting in fewer available muscle fibers. Our nerves communicate with our muscles by releasing neurotransmitters (type of chemicals) which fit precisely into receptor sites on the muscle cells (muscle receptor cells). Consequently, there is inadequate communication between the nerves and affected muscles; the muscles cannot contract properly and become tired and weak very easily - with fewer receptor sites the muscles receive fewer nerve signals.