Parkinson's disease primarily affects which aspect of nervous system function?

• A. Digestive function
• B. Sensory perception
• C. Autonomic regulation
• D. Motor function

Answer: (D)

Parkinson's disease is a neurodegenerative movement disorder caused by loss of dopamine-producing neurons in the substantia nigra, which disrupts the basal ganglia circuits that coordinate and smooth voluntary movement. Because these circuits control initiating and modulating motor activity, the most prominent and defining effects are motor: tremor at rest, slowed movement, stiffness, and balance difficulties. While non-motor features like autonomic changes or sensory issues can occur, the primary impact is on motor function due to the disrupted dopaminergic regulation of movement.