Myasthenia gravis is also called MG. It is an illness that affects the muscles and the nerves. Nerves send signals from the brain to tell the muscles to move. With MG, the signal is blocked at the muscle. Early in the disease the muscle weakness is mild but the muscles may become weaker over time. MG may affect muscles attached to bones. It mostly affects muscles in your eyes, face, or those used for chewing and swallowing. However, any part of your body may be affected. It only affects muscles that you must think about to control like those used to walk, roll over, or move your eyes. MG does not affect your heart muscle or the muscles in your bowels.