“The effects of parkinsonism depend on why it happens. Most parkinsonian conditions affect parts of your brain responsible for movement. That means you move more slowly. You also may have muscle tremors, causing you to shake.

Under normal circumstances, your brain uses chemicals known as neurotransmitters to control how your brain cells (neurons) communicate with each other. When you have Parkinson’s disease, you don’t have enough dopamine, one of the most important neurotransmitters.

When your brain sends activation signals that tell your muscles to move, it fine-tunes your movements. The neurons that fine-tune your movements need dopamine. Without it, they can’t do their job correctly. That’s why lack of dopamine causes the slowed movements and tremors symptoms of Parkinson’s disease.

With lack of dopamine, the basal ganglia (a key area of your brain) start to deteriorate. As they do, you lose the abilities they once controlled. As Parkinson’s disease gets worse, the symptoms expand and intensify. Later stages of the disease often affect how your brain functions, causing dementia-like symptoms and depression.”

Cleveland Clinic (Parkinsonism: What It Is, Causes & Types)