Final answer:
The parkinsonian side effects of antipsychotic medications are due to their impact on the nigrostriatal tract, which is involved in regulating motor activity through dopaminergic neurons originating from the substantia nigra.
Step-by-step explanation:
The parkinsonian side effects of antipsychotic medications are most often attributed to the effects of these drugs on the nigrostriatal tract. This dopaminergic pathway originates from the substantia nigra pars compacta (SNc) and projects into the dorsal striatum, where dopamine interacts with GABAergic and cholinergic neurons to modulate motor activity. In Parkinson's disease (PD), the loss of dopaminergic neurons in the SNc leads to a reduction of dopaminergic innervation in the basal ganglia, which manifests in motor symptoms such as bradykinesia, tremor, muscular rigidity, and postural instability. Antipsychotic drugs often block dopamine receptors, which can result in similar motor impairments resembling PD. Therefore, the correct answer to the student's question is C. Nigrostriatal tract.