Parkinson's disease belongs to a group of conditions called motor system disorders. Parkinson's and related disorders are the result of the loss of dopamine-producing brain cells.
Dopamine is a chemical messenger responsible for transmitting signals within the brain.
Parkinson's disease occurs when certain nerve cells, or neurons, die or become impaired. Normally, these neurons produce dopamine. Loss of dopamine causes the nerve cells to fire out of control, leaving patients unable to direct or control their movement in a normal manner. Patients may also have difficulty walking, talking, or completing other simple tasks. The disease is both chronic and progressive.