In Parkinson disease, overactivity of the subthalamic nucleus contributes to bradykinesia by driving excessive output from the globus pallidus internus. Reduced inhibitory input from which structure accounts for this subthalamic overactivity?
- A External segment of the globus pallidus ✓
- B Internal segment of the globus pallidus
- C Substantia nigra pars compacta
- D Caudate nucleus
Correct answer: A. External segment of the globus pallidus
Explanation
In the indirect pathway, the striatum inhibits the external globus pallidus (GPe), which in turn tonically inhibits the subthalamic nucleus. Dopamine loss in Parkinson disease increases striatal inhibition of GPe, so GPe inhibition of the subthalamic nucleus falls, and the excited subthalamic nucleus drives GPi and substantia nigra pars reticulata, suppressing the thalamus. The substantia nigra pars compacta acts via dopaminergic modulation of the striatum, not by directly inhibiting the subthalamic nucleus.
Reference: Ganong's Review of Medical Physiology, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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