Muscle is a special kind of tissue that enables our bodies to move. It is under the control of the nervous system, which processes messages to and from all parts of the body. Sometimes the nerve cells, or neurons, that control the muscles become diseased or injured. When that happens, a person loses the ability to move the muscles voluntarily, and we say that the person is paralyzed.
Paralysis of the muscles of the face, arm, and leg on one side of the body is called hemiplegia ("hemi" means "half") and usually results from damage to the opposite side of the brain. Damage to the nerves of the spinal cord affects different parts of the body, depending on the amount of damage and where it occurred. Paralysis of both lower limbs is called paraplegia, and paralysis of both arms and both legs is called quadriplegia. Paralysis may be temporary or permanent, depending on the disease or injury. Because paralysis can affect any muscle in the body, a person may lose not only the ability to move but also the ability to talk or to breathe unaided.