Parkinson's disease occurs when certain nerve cells, or neurons, die or become impaired.
Normally, these neurons produce dopamine and other neurotransmitters. Dopamine is a chemical messenger responsible for transmitting signals within the brain.
Loss of dopamine results in patients being unable to direct or control their movement in a normal manner. Parkinson's is not usually inherited.
Revised and reviewed by Prof Carr February 2015. Reviewed by Dr Andrew Rose-Innes, MD, Department of Neurology, Yale University School of Medicine, New Haven.