Neurology involves the treatment of disease or impaired function of the brain, spinal cord, peripheral nerves, muscles, and autonomic nervous system, as well as the blood vessels that relate to these structures. Neurologists treat patients who have a variety of disorders, including headaches, strokes, seizure disorders, multiple sclerosis, dystonia, muscular dystrophy, peripheral nerve disease, learning disorders, traumatic injuries to the nervous system, Parkinson's, Huntington's, and Alzheimer's disease. Some neurologists are also engaged in neurological rehabilitation. Many neurological problems are characterized by pain and can be chronic, debilitating, and difficult to treat. A large portion of the practice of neurology is consultative, but the neurologist may also be the primary physician. The specialty has close links with psychiatry, with which it maintains a combined certification board.