Separated by the internal capsule into the caudate nucleus and the putamen. Major input structure of the basal ganglia. > receives prominent projection from cerebral cortex, brain stem, and thalamus: globus pallidus. Consist of two separate nuclei; external and internal segments. > internal segment is one of major output structures. > external segment is part of their intrinsic circuitry: substantia nigra. > contains along with portions of the ventral tegmental area and other midbrain areas dopaminergic cells. > forms together with the internal segment of the globus pallidus one single output structure divided by the internal capsule. > these project heavily to the striatum and to the other nuclei: subthalamic nucleus. Small nucleus situated between the thalamus and the substantia nigra. Receives projections from the external segment of the globus pallidus, the cerebral cortex, thalamus, and brain stem and send output to both segments of the globus pallidus and to the substantia nigra pars reticulata.