Parkinson's disease

Parkinson's disease is a nervous system disorder that affects movement and gets worse over the years.

Deep in the brain, in an area called the substantia nigra, there are neurons that make dopamine, a chemical messenger. Dopamine is what makes each movement smooth and intentional instead of jerky. In Parkinson's, those neurons are damaged and die, and that is where most of the symptoms come from. What is surprising is how much is lost silently: by the time symptoms are finally noticeable, most people have already lost 60 to 80 percent or more of those dopamine-producing cells. On top of that, in most people with Parkinson's, the damaged neurons have Lewy bodies inside them, abnormal clumps of a protein called alpha-synuclein, like lumps of flour that never dissolved. Why those lumps form is something nobody knows yet.