Motor System II: Basal Ganglia

Abstract

The term " basal ganglia " originally included the deep telencephalic nuclei: the caudate, putamen, globus pallidus, the claustrum, and nucleus accumbens) The globus pallidus and putamen are lens-shaped and are called lenticular nuclei. Collectively, the putamen and caudate are called the corpus striatum. Additional structures now included within this group are the substantia nigra, the subthalamic nuclei, the ventral tegmental area. and the ventral pallidum. One is very familiar with disease of the basal ganglia due to the widespread presence of Parkinson's disease with its tremor at rest. I. Anatomy The caudate and putamen have the same structure (Table 10.1) and are continuous anteriorly. The globus pallidus has two sectors: a medial or inner and a lateral or outer. The substantia nigra has two components: a ventral pars reticularis, which is identical in structure and function to the medial sector of the globus pallidus, and a dorsal darkly staining component—the pars compacta—which contains large dopamine-and melanin-containing neurons. The nuclei of the basal ganglia can be categorized as (1) input nuclei (caudate, putamen, and accumbens), (2) intrinsic nuclei (lateral segment of the globus pallidus, subthalamic nucleus, pars compacta of the substantia nigra, and the ventral tegmental area), and (3) output nuclei (medial segment of the globus pallidus, pars reticularis of the substantia nigra, and the ventral pallium). The consideration of the chemical and pharmacological anat-omy of transmitters and circuits within the system will provide an understanding of function and dysfunction within this system. It should be noted that the nuclei of the basal ganglia, the circuits involving the basal ganglia, the cortical areas project-ing to the basal ganglia, the cerebellar nuclei relating to the basal ganglia, and the reticular formation (which has connections with both the cortex and the basal gan-glia) were once grouped together as an " extrapyramidal system. " The term " extrapyramidal disorders " was used to refer to the effects of lesions within the basal ganglia system. However, the term " extrapyramidal " was also utilized to refer to the descending pathways: corticorubral spinal and corticoreticulospinal that were