2. Myasthenia gravis is an autoimmune disease that produces extreme muscle weakness and fatigue due to the breakdown of ACh receptor sites at the neuromuscular junction. Muscular dystrophy is a collection of diseases that produces muscular degeneration. Polio is a contagious viral disease that attacks spinal motor neurons, causing some degree of paralysis. Accidental spinal injury results in the loss of voluntary movement produced by nerves below the level of injury. (LO6)