The antagonistic functions of the direct and indirect pathways are modulated by the
substantia nigra pars compacta (SNc), which produces dopamine. Special D1-
receptors in the basal ganglia are excited by dopamine, favoring the direct pathway,
whereas specialized D2-receptors in the basal ganglia are inhibited in presence of
dopamine and favor the indirect pathway. Through these mechanisms the body is
able to maintain balance between excitation and inhibition of motion. Lack of balance
in this delicate system leads to pathologies such as Parkinson's disease.