Located in the midbrain crus cerebri and forming the outer/anterior/ventral part of the subst.nigra. Here the nerve cell bodies are less tightly packed cf. with substantia nigra, pars compacta, SNc.
SNr exhibits inhibitory (GABA-erg) tonic self-activity with a discharge frequency around 70 Hz and
contains a few dopaminergic neurons.
SNr and pale core inner part ( GPi) can, with certain reservations, be considered as a functional unit: GPi-SNr.