ABSTRACT

This chapter provides an overview of basal ganglia (BG) anatomy. The BG contain two major components—striatum and pallidum. Both are large and heterogeneous structures associated with complex traditional anatomical terminology. Unlike the cerebral cortex, which contains glutamatergic projection neurons, the striatum and pallidum contain mostly GABAergic projection neurons. As the input nucleus, the striatum receives extensive excitatory inputs from the cortex and thalamus and sends GABAergic outputs to the pallidum. As the output nucleus, the pallidum sends GABAergic projections to many areas in the brainstem, thalamus, subthalamus, and epithalamus. Outputs from the BG are thus in a position to influence skeletomotor, autonomic, and neuroendocrine effectors. The basic BG pathway, also known as the direct pathway, involves two consecutive inhibitory synapses. The net effect of activating this disinhibitory pathway is selective activation of target neurons receiving pallial innervation. In addition, there are also other pathways, most notably the indirect pathway, that can exert the opposite effect on the targets of the BG.