Parkinson's disease. Artwork of a coronal section (frontal) through a brain, showing areas affected by Parkinson's disease. The magnified view (lower centre) is an axial (horizontal) section through the upper brainstem. Parkinson's disease is caused by a degeneration of nerve tissue within the basal ganglia of the brain, particularly the substantia nigra (black). Normal nerve pathways (black, left) contrast with dysfunctional pathways (red, right). These pathways are mediated by the brain chemical dopamine (molecules at far left and right). This degeneration leads to loss of muscle control, and tremors and a shuffling walk develops. Treatment includes dopamine drugs. There is no cure.