| Globus pallidus | |
|---|---|
 Globus pallidus (in red) shown within the brain | |
 Dopamine-loops in Parkinson's disease | |
| Details | |
| Part of | Basal ganglia |
| Identifiers | |
| Latin | globus pallidus |
| Acronym(s) | GP |
| MeSH | D005917 |
| NeuroNames | 231 |
| NeuroLex ID | birnlex_1234 |
| TA98 | A14.1.09.518 |
| TA2 | 5569 |
| FMA | 61835 |
| Anatomical terms of neuroanatomy | |
Theglobus pallidus (GP), also known aspaleostriatum ordorsal pallidum,[1] is a major component of thesubcorticalbasal ganglia in thebrain. It consists of two adjacent segments, oneexternal (or lateral), known in rodents simply as theglobus pallidus, and oneinternal (or medial). It is part of thetelencephalon, but retains close functional ties with thesubthalamus in thediencephalon – both of which are part of theextrapyramidal motor system.[2]
The globus pallidus receives principal inputs from thestriatum, and principal direct outputs to thethalamus and thesubstantia nigra. The latter is made up of similar neuronal elements, has similar afferents from the striatum, similar projections to the thalamus, and has a similarsynaptology. Neither receives direct cortical afferents, and both receive substantial additional inputs from theintralaminar thalamic nuclei.
Globus pallidus isLatin 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[3] and perpendicular to the afferentstriatopallidalaxons.[4] There are only a few small local circuitry neurons.[citation needed]
The globus pallidus is traversed by the numerousmyelinated axons of thestriatopallidonigral 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.[5][6]
In primates, the globus pallidus is divided into two parts by a thinmedial medullary lamina.[7] These are theinternal globus pallidus (GPi) and theexternal globus pallidus (GPe); both are composed of closed nuclei surrounded by myelinic walls.[citation needed]
Theventral pallidum lies within thesubstantia innominata (Latin for unnamed substance) and receives efferent connections from the ventralstriatum (thenucleus accumbens and theolfactory tubercle). It projects to the dorsomedial nucleus of the dorsalthalamus, which, in turn, projects to theprefrontal cortex; it also projects to thepedunculopontine nucleus andtegmental 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]
The globus pallidus is a structure in the brain involved in the regulation of voluntary movement.[8] It is part of thebasal ganglia, which, amongmany other functions, regulate movements that occur on the subconscious level.[citation needed]
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 beingaspiration pneumonia.[citation needed]
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.[citation needed]
The two pallidal nuclei and the two parts of the substantia nigra (thepars compacta andpars reticulata) constitute a high-frequency autonomous pacemaker.[9] (seeprimate basal ganglia#Pallidonigral set and pacemaker)
The two parts receive successively a large quantity ofGABAergic axonal terminal arborisations from thestriatum through the dense striato-pallidonigral bundle. The synaptology is very peculiar (seeprimate basal ganglia system).[5][6] The striatal afferents contribute more than 90% of synapses.[citation needed]The two pallidal nuclei receive dopaminergic axons from the pars compacta of the substantia nigra.
This area of the basal ganglia receives input from another area, called the striatum, which has two parts, thecaudate nucleus and theputamen. This data is routed to the thalamus, either directly or indirectly. In the case of the interna, one area of the globus pallidus, the structure can feed directly to the thalamus. The externa, which lies on the outside of this structure, feeds information to the interna, where it can be passed on to the thalamus.[citation needed]
Infarction of the globus pallidus can be seen withanoxic brain injury,carbon monoxide poisoning and drug overdoses (MDMA andheroin), with the insult classically beingbilateral. Bilateral calcification can occur in alentiform shape with aggressiveparenteral nutrition. Encephalopathy, as can occur withcirrhosis orLeigh syndrome, also causes globus pallidus abnormalities, making them bright onMRI T1 sequences in liver disease and on bright on T2 sequences with Leigh syndrome. Additional substances that can accumulate in the basal ganglia include heavy metals (such asgadolinium, iron andcopper),calcium andamyloid withhypothyroidism.[citation needed]
Clumps of disorganized nerve tissue, can accumulate inside the globus pallidus withneurofibromatosis type I, causing severe neurologic dysfunction. The pallidus can also be destroyed by rare metabolic disorders such asPKAN,methylmalonic acidemias andmaple syrup urine disease.[10]
Though damage to the globus pallidus can causemovement disorders, diseases likeParkinson's andessential tremor can paradoxically be treated bysurgically inducing lesions in the nuclei using ultrasound,Gamma knife, or more rarely open surgery. The nucleus can also be artifically stimulated usingdeep 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 causedysarthria.[11]
The origin of the name is not established. It was used byJoseph Dejerine (1906) but not bySantiago Ramón y Cajal (1909–1911).[citation needed]
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 theTerminologia Anatomica.[citation needed]
For a long time the globus pallidus was linked to the putamen and termed thelentiform nucleus (nucleus lenticularis or lentiformis), a heterogeneous anatomical entity that is part of thestriatum rather than the pallidum. The link with thesubstantia 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.[citation needed]
In rodents, the globus pallidus internus is also known as theentopeduncular nucleus.[citation needed]
