Which brain structure is primarily affected in Parkinson disease, leading to motor symptoms?

• A. Basal ganglia
• B. Cerebellum
• C. Hippocampus
• D. Spinal cord

Answer: (A)

Basal ganglia function in coordinating and initiating movement. In Parkinson's disease, degeneration of dopamine-producing neurons in the substantia nigra leads to disrupted signaling within the basal ganglia circuits. This shifts the balance between the direct and indirect pathways, making it harder to start and smoothly control movements, which shows up as tremor at rest, bradykinesia, rigidity, and postural instability. The cerebellum helps with movement timing and precision but Parkinsonian motor symptoms arise from basal ganglia dysfunction, not cerebellar damage. The hippocampus is involved in memory, and the spinal cord carries motor commands, but the primary pathology driving these motor symptoms is in the basal ganglia.