ABSTRACT
The basal ganglia consists of several extensively interconnected structures, the striatum, the globus pallidus, the substantia nigra and the subthalamic nucleus. Most inputs to the basal ganglia are from the cerebral cortex and enter the striatum. The output of the basal ganglia emerges from the pars interna of the globus pallidus, and the substantia nigra pars reticulata, to go to the thalamus. The globus pallidus pars interna (GPi) and substantia nigra pars reticulata (SNpr) provide basal ganglia output for limb and facial movements, and part of the SNpr is concerned with eye movements. The globus pallidus pars externa (GPe) receives its striatal connections from the γ-Aminobutyrate (GABA)/ENK medium spiny neurons. The GPe neurons are GABAergic and go mostly to the subthalamic nucleus, but projections to GPi and SNpr have also been described. Corticostriate axons terminate on the major neuron type in the striatum, the medium spiny neuron.
