Parkinson's disease. Illustration of the brain, depicting the neurological disorder of Parkinson's disease. A coronal section through the brain is seen, with two elderly figures in a bent posture superimposed. Parkinson's disease is caused by a degeneration of nerve tissue within the basal ganglia (pink areas, at centre) of the brain. As a result, nerve pathways down the spinal cord are altered. Contracted muscle is prevented from relaxing, causing tremor, joint rigidity, and slow movement. Parkinson's disease affects the elderly. It progresses from a slight hand tremor, to an unbalanced, bent-over, shuffling walk. Treatment includes dopamine drugs. There is no cure.