The globus pallidus ( GP), also known as paleostriatum or dorsal pallidum, is a major component of the Cerebral cortex 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 synapse. Neither receives direct cortical afferents, and both receive substantial additional inputs from the intralaminar thalamic nuclei.
Globus pallidus is Latin for "pale globe".
Structure
The globus pallidus is traversed by the numerous axons of the striatopallidonigral bundle that give it the pale appearance from which it is named.
The ultrastructure is very peculiar, as the long dendrites are everywhere, without discontinuity, covered by synapses.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: 75–93di Figlia, M., Pasik, P., Pasik, T. (1982) A Golgi and ultrastructural study of the monkey globus pallidus. J. Comp. Neurol. 212: 53–75
Parts
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 Tegmentum 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.
Function
/ref> It is part of the basal ganglia, which, among many other functions, regulate movements that occur on the subconscious level.
The globus pallidus has a predominantly inhibitory effect on movement regulation, balancing cerebellar excitation. Pulsatile and regular interaction between these complementary systems allows smooth and controlled movement. Imbalances can result tremors, jerks, dystonia, chorea and progressive motor weakness ending in diaphragmatic dysfunction, with the most common cause of mortality in most neurodegenerative disorders being aspiration pneumonia.
The basal ganglia acts on a subconscious level, requiring no conscious effort to function. When someone makes a decision to engage in an activity such as petting a dog, for example, these structures help to regulate the movement to make it as smooth as possible, and to respond to sensory feedback. Likewise, the globus pallidus is involved in the constant subtle regulation of movement that allows people to walk and engage in a wide variety of other activities with a minimal level of disruption.
Pallidonigral pacemaker
Common afferents
Pathway
Disease
Neurofibroma, can accumulate inside the globus pallidus with neurofibromatosis type I, causing severe neurologic dysfunction. The pallidus can also be destroyed by rare metabolic disorders such as PKAN, methylmalonic acidemias and maple syrup urine disease.
Though damage to the globus pallidus can cause movement disorders, diseases like Parkinson's and essential tremor can paradoxically be treated by pallidotomy in the nuclei using ultrasound, Gamma knife, or more rarely open surgery. The nucleus can also be artificially stimulated using deep brain stimulation in which a battery pack is inserted into the chest wall and electrical leads run up the neck and into the brain from the back of the skull. The aim of these procedures is to reduce involuntary muscle tremors and improve extrapyramidal symptoms associated with neurodegeneration, though they can impact intellectual function and cause dysarthria.McCartney, L. K., Bau K., Stewart K., Botha B., Morrow A., (2016), Pallidotomy as a treatment option for a complex patient with severe dystonia, Dev. Med. Child Neurol. 2016 58: (68–69) http://onlinelibrary.wiley.com/doi/10.1111/dmcn.13070/epdf
History
As the elements in no way have the shape of a globe, throughout the 20th century scientists proposed a simpler term (a neuter adjective), pallidum (meaning "pale"). Propositions include those by Foix and Nicolesco (1925), the Vogts (1941), Crosby et al. (1962) and the Terminologia Anatomica.
For a long time the globus pallidus was linked to the putamen and termed the lentiform nucleus (nucleus lenticularis or lentiformis), a heterogeneous anatomical entity that is part of the striatum rather than the pallidum. The link with the substantia nigra pars reticulata was stressed very early on due to the similarities in dendritic arborisation (and they are sometimes known as the pallidonigral set) but, in spite of strong evidence, this association remains controversial.
Animal Studies
See also
- Lentiform nucleus
External links
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