Globus pallidus

The globus pallidus (GP), also known as paleostriatum or dorsal pallidum, is a major component of the subcortical basal ganglia in the brain. It consists of two adjacent segments, one external (or lateral), known in rodents simply as the globus pallidus, and one internal (or medial). It is part of the telencephalon, but retains close functional ties with the subthalamus in the diencephalon – both of which are part of the extrapyramidal motor system.

The globus pallidus receives principal inputs from the striatum, and principal direct outputs to the thalamus and the substantia nigra. The latter is made up of similar neuronal elements, has similar afferents from the striatum, similar projections to the thalamus, and has a similar synaptology. Neither receives direct cortical afferents, and both receive substantial additional inputs from the intralaminar thalamic nuclei.

Globus pallidus is Latin for "pale globe".

Pallidal nuclei are made up of the same neuronal components. In primates, almost all pallidal neurons are very large, parvalbumin-positive, with very large dendritic arborizations. These have the peculiarity of having the three-dimensional shape of flat discs, parallel to one another, parallel to the border of the pallidum and perpendicular to the afferent striatopallidal axons. There are only a few small local circuitry neurons.^{[citation needed]}

The globus pallidus is traversed by the numerous myelinated axons of the striatopallidonigral bundle that give it the pale appearance from which it is named.^{[citation needed]}

The ultrastructure is very peculiar, as the long dendrites are everywhere, without discontinuity, covered by synapses.

In primates, the globus pallidus is divided into two parts by a thin medial medullary lamina. These are the internal globus pallidus (GPi) and the external globus pallidus (GPe); both are composed of closed nuclei surrounded by myelinic walls.^{[citation needed]}

The ventral pallidum lies within the substantia innominata (Latin for unnamed substance) and receives efferent connections from the ventral striatum (the nucleus accumbens and the olfactory tubercle). It projects to the dorsomedial nucleus of the dorsal thalamus, which, in turn, projects to the prefrontal cortex; it also projects to the pedunculopontine nucleus and tegmental motor areas. Its function is to serve as a limbic-somatic motor interface, and it is involved in the planning and inhibition of movements from the dorsal striatopallidal complex.^{[citation needed]}