Incidence In the United States, it is estimated that approximately 14 out of every 100,000 people have myasthenia gravis. However, it is likely underdiagnosed and may occur at an even higher rate. MG occurs in women most commonly between the ages of 10 and 30. In men it is most common between the ages of 60 and 80. Every time your body moves, whether you're walking, talking or breathing, a muscle contracts.
Muscles work by transforming chemical energy into mechanical energy, which moves the human body.
Skeletal muscle in particular is under our voluntary control, meaning that we can consciously send messages from the brain telling it, in effect, what to do. The messages that are sent are biochemical and they travel from the brain through the spinal cord through the nerves to the muscle. If we want to move our arm, for example, our brain sends a biochemical message that eventually reaches the arm muscles causing the arm to move. The nerves that command the muscle are called motorneurons, and the place where the nerve meets the muscle is called the neuromuscular junction, the site where myasthenia gravis does it damage. One of the biochemicals involved with the transfer of information through the nervous system is acetylcholine, or ACh.