Paralysis is loss of muscle function of one or more muscles in the body. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. Paralysis is most often caused by damage in the nervous system, especially the spinal cord. Drugs that interfere with nerve function, such as curare, can cause paralysis. There are many known causes for paralysis, and perhaps more yet to be discovered. Other major causes are stroke, trauma with nerve injury, poliomyelitis, amyotrophic lateral sclerosis (ALS), botulism, spina bifida, multiple sclerosis, and Guillain-Barré syndrome. Temporary paralysis occurs during REM sleep, and dysregulation of this system can lead to episodes of waking paralysis.