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|Brain: Globus pallidus|
|Globus pallidus labeled at bottom right.|
|DA-loops in PD|
The globus pallidus (Latin for "pale globe") is a sub-cortical structure of the brain. It is a major element of the basal ganglia system. In this system, it is a major constituent of the basal ganglia core, which consists of the striatum and its direct targets: globus pallidus and substantia nigra. The last two are made up of the same neuronal elements, have a similar main afferent (the dorsal striatum), have a similar synaptology, and do not receive cortical afferents. It was recently discovered  to play an active part in pre-filtering external stimuli and may help reduce the amount of irrelevant information the brain needs to store.
History of nameEdit
The origin of the name is not established. It was known by Dejerine (1906) but not by Santiago Ramón y Cajal (1909-1911). As the elements in no way have the shape of a globe, Foix and Nicolesco (1925), the Vogts (1941), Crosby et all.(1962) followed by the Terminologia anatomica proposed the simpler term (neuter adjective) of pallidum (pale). During a long period the globus pallidus was unduly linked to the putamen in the lentiform nucleus (nucleus lenticularis or lentiformis). This was a heterogeneous anatomical entity that is part of the striatum rather than the pallidum. The link with the substantia reticulata was stressed very early on due to the similarities in dendritic arborisation, but in spite of solid arguments this link is still not widely accepted. The two however constitute a particular set of the basal ganglia system (the pallidonigral set).
In primates, the dorsal pallidum, or globus pallidus, is divided into two segments by the medial medullary lamina. A frequent nomenclature uses the adjectives internal and external to refer to the two divisions of the globus pallidus. The medial segment of the dorsal pallidum, internal globus pallidus (GPi), and lateral division of the dorsal pallidum, external globus pallidus (GPe), are thus the two parts of the dorsal pallidum that are two closed nuclei surrounded everywhere by myelinic walls.
The ventral pallidum lies within the substantia innominata (Latin for un-named substance) and receives efferent connections from the ventral striatum (nucleus accumbens and olfactory tubercle). The ventral pallidum projects to the dorsomedial nucleus of the dorsal thalamus, which projects to the prefrontal cortex. The ventral pallidum also projects to the pedunclopontine nucleus and tegmental motor area. The function of the ventral pallidum is limbic-somatic motor interface for the planning and inhibition of movements from the dorsal striatopallidal complex.
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.
The globus pallidus is traversed by the numerous myelinated axons of the striato-pallidonigral bundle that give it the pale appearance from which it is named.
The two pallidal nuclei and the two nigral (pars compacta and pars reticulata) parts constitute a high-frequency autonomous pacemaker (see primate basal ganglia system#Pallido-nigral_set_and_pacemaker)
The two parts receive successively a large quantity of GABAergic axonal terminal arborisations from the striatum through the dense striato-pallidonigral bundle. The synaptology is very peculiar (see primate basal ganglia system).The striatal afference contribute for more than 90% of synapses.[How to reference and link to summary or text] The two pallidal nuclei receives dopaminergic axons from the pars compacta of the substantia nigra.
- ↑ Yelnik, J., Percheron, G., and François, C. (1984) A Golgi analysis of the primate globus pallidus. II- Quantitative morphology and spatial orientation of dendritic arborisations. J. Comp. Neurol. 227:200-213
- ↑ Percheron, G.,Yelnik, J. and François. C. (1984) A Golgi analysis of the primate globus pallidus. III-Spatial organization of the striato-pallidal complex. J. Comp. Neurol. 227: 214-227
- ↑ 3.0 3.1 Fox, C.A., Andrade, A.N. Du Qui, I.J., Rafols, J.A. (1974) The primate globus pallidus. A Golgi and electron microscopic study. J. Hirnforsch. 15: 75-93
- ↑ 4.0 4.1 di Figlia, M., Pasik, P., Pasik, T. (1982) A Golgi and ultrastructural study of the monkey globus pallidus. J. Comp. Neurol. 212: 53-75
- ↑ Surmeier, D.J., Mercer, J.N. and Savio Chan, C. (2005) Autonomous pacemakers in the basal ganglia: who needs excitatory synapses anyway? Cur. Opin.Neurobiol. 15:312-318.
- BrainMaps at UCDavis Globus%20pallidus
- Dictionary at eMedicine Globus+pallidus
- Dictionary at eMedicine Paleostriatum
- Diagram at uni-tuebingen.de
Human brain, cerebrum, Interior of the cerebral hemispheres—Rostral Basal ganglia and associated structures (TA A14.1.09.321–552, GA 9.832–837)
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