Parkinson's disease is a progressive neurological disorder that affects movement and coordination. It is caused by the gradual loss of dopamine-producing cells in a specific brain region called the substantia nigra. Dopamine is a neurotransmitter that helps control movement and emotional responses.

As dopamine levels decrease, symptoms of Parkinson's disease begin to appear. These can include tremors or shaking, stiffness, difficulty with balance and coordination, and slowness of movement. Other symptoms may include changes in speech, mood, and cognitive function.