Extrapyramidal system, and basal ganglia components

In order to discuss the organization of dopaminergic pathways, an overview of basal ganglia components and circuits is first presented. These circuits form the system that was traditionally defined as extrapyramidal and is now indicated with the more straightforward definition of basal ganglia . 

The main structures of the basal ganglia, defined nowadays in neuroscience as a system of functionally related and anatomically interconnected centers and circuits, include the striatum, the GP, the STh, and the SN (Fig. 16). The umbrella term of basal ganglia therefore groups structures located in the telencephalon (the striatum and GP), diencephalon (the STh) and brain stem (the midbrain dopaminergic cell groups). 

The striatum comprises the caudate nucleus and the putamen (the neostriatum , frequently indicated, as in this chapter, simply as striatum ) and the ventral striatum. The striatal components represent the key regions for DA release and action in the basal ganglia, and are dealt with in Sections 5 and 7. 

EP is frequently defined nowadays as GPi (or medial GP) also in rodents, adopting in rodents the subdivision of the GP in two segments (cf. the rat atlases of Paxinos and Watson (1998) and Swanson (1992) cf. also the mouse atlases of Hof et al. (2000) and Paxinos and Franklin (2001)). The majority of neurons of both the GP divisions are large and fusiform or triangular, with very long, thick, smooth and sparsely branching dendrites (see for reviews Heimer et al., 1995, and Gerfen, 2004). The term ventral pallidum refers to the ventral or subcommissural part of the pallidal complex (see Section 7). 

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