<prompt> Cause of myasthenia gravisDecreased release of Ach at NM junctionLoss of muscles fibersDestruction of receptors by antibodyDestruction of receptors by autolysis  <response>: Myasthenia gravis is rare autoimmune disease caused by the formation of circulating antibodies to the nicotinic A-ch receptors. These antibodies destroy some of the receptors and bind others to neighboring receptors. The disease is characterized by rapid onset of fatigue with marked generalized weakness of muscles. The most commonly affected muscles are: extraocular muscles, facial, swallowing and mastication muscles.Ref: Textbook of physiology, Dir. Prof. AK Jain, 5th edition. 