Myasthenia gravis is a neuromuscular disorder characterized by weakness and fatigue of muscles due to autoantibodies against acetylcholine receptors, resulting in a decreased number of receptors. It is caused by antibodies that decrease available acetylcholine receptors by damaging postsynaptic membranes, blocking receptor sites, or accelerating receptor turnover. Treatment involves anticholinesterases, immunosuppressants, thymectomy, plasmapheresis, and IVIg. Disease severity is classified using the Osserman classification system.