In the substantia nigra pars compacta, dopaminergic neurons degenerate in Parkinson disease. The substantia nigra projects dopaminergic fibres primarily to which striatal nucleus, forming the nigrostriatal pathway?
- A Caudate nucleus and putamen (dorsal striatum) ✓
- B Nucleus accumbens (ventral striatum)
- C Globus pallidus interna
- D Subthalamic nucleus
Explanation
The nigrostriatal pathway projects from the substantia nigra pars compacta (SNc) to the dorsal striatum (caudate nucleus and putamen), where dopamine acts on D1 receptors (activating the direct pathway) and D2 receptors (inhibiting the indirect pathway) to modulate basal ganglia motor circuitry. Loss of these dopaminergic projections in Parkinson disease disinhibits the indirect pathway and reduces excitation via the direct pathway, ultimately increasing GPi inhibition of the thalamus and reducing cortical motor activation. The mesolimbic pathway (SNc/VTA → nucleus accumbens) is separate and mediates reward rather than motor control.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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