The hallmark pathological feature of PD is the progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta, a region of the brain involved in movement control. Dopamine is a neurotransmitter that plays a critical role in regulating motor function and coordination. This neuronal loss leads to a significant reduction in dopamine levels in the basal ganglia, impairing motor control and contributing to the development of motor symptoms such as bradykinesia, tremor, rigidity, and postural instability.