Paralysis is a loss of muscle functionof one or more muscles. Paralysis can be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage as well as motor. A paralysis accompanied by involuntary tremors is usually called "palsy" The four most common causes of paralysis are stroke, head injury, spinal cord injury and multiple sclerosis others include ,cancer, cerebral palsy, spina bifida and others.