Input to the basal nuclei is primarily received by the striatum (caudate nucleus and putamen), and output predominantly leaves from the globus pallidus. Many structures send input to the striatum, including all areas of the cerebral cortex, thalamic nuclei, subthalamic nucleus, brainstem, and substantia nigra. To understand how the basal nuclei integrates all of this incoming information to influence motor activity, two simplified neuronal loops are described: the direct pathway and the indirect pathway.