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. The four primary
symptoms of Parkinson's are tremor or trembling in hands, arms, legs,
jaw, and face; rigidity or stiffness of the limbs and trunk; bradykinesia,
or slowness of movement; and postural instability or impaired balance
and coordination. Patients may also have difficulty walking, talking,
or completing other simple tasks. The disease is both chronic and
progressive. Parkinson's is not usually inherited. Early symptoms
are subtle and occur gradually.
