Paralysis
Paralysis, loss of voluntary movement in a part of the human body, caused by disease or injury anywhere along the motor-nerve path from the brain to the muscle fiber. Paralysis may result from injury, poisoning, infection, hemorrhage, occluded blood vessels, or tumors. Occasionally paralysis is due to congenital deficiency in motor-nerve development. Permanent paralysis results from extensive damage to nerve cells or to a nerve trunk; severely damaged nerve cells cannot regenerate. Transient or incomplete paralysis, called paresis, is often caused by infections, trauma, or poisons that temporarily suppress motor activity but do not extensively damage nerve cells. Because most of the motor nerves from either half of the brain supply the opposite side of the body, lesions in one part of the brain usually produce paralyses in the opposite half of the body. Paralysis of one limb is known as monoplegia; paralysis of two limbs on the same side of the body as hemiplegia; paralysis of both l