Myasthenia gravis (MG) is a rare, chronic, autoimmune, neuromuscular condition characterized by weakness of voluntary muscles that increases with exercise and recovers with rest. Generalized myasthenia gravis (gMG) is a severe form of MG that can include weakness of multiple muscle groups such the limbs, neck, diaphragm, and eye muscles.
How Voluntary Muscles Work
How Voluntary Muscles Work
Let's review how voluntary muscles work. Voluntary muscles in the body are controlled by nerve signals, or neurotransmitters, from the brain. The area where the nerve signals from the brain meet the muscle fiber is called the neuromuscular junction. The neuromuscular junction contains many receptors called acetylcholine receptors. These receptors are essential for initiating muscle movement.
When signals from the brain travel through the nerve, the nerve endings release a neurotransmitter called acetylcholine into the neuromuscular junction. The acetylcholine binds to acetylcholine receptors to stimulate the muscle fibers and enable them to contract.
What Causes gMG?
What Causes gMG?
In people with gMG, the immune system doesn't function correctly. Instead of helping the body fight off sickness by attacking intruders like bacteria and viruses, the body makes antibodies against the acetylcholine receptors. These antibodies switch on another part of the immune system, called the complement cascade, and damage the neuromuscular junction. As a result, the neuromuscular junction can no longer function and nerve impulses are not transmitted to the muscle, causing weakness.