Basal ganglia and Talk:WGN (AM): Difference between pages

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Caption = Coronal slices of human brain showing the [[basal ganglia]], [[globus pallidus|globus pallidus: external segment]] (GPe), [[subthalamic nucleus]] (STN), [[globus pallidus|globus pallidus: internal segment]] (GPi), and [[substantia nigra]] (SN). |

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Caption2 = Coronal section of brain immediately in front of pons. (Not all basal ganglia are visible, but [[caudate nucleus]] and [[substantia nigra]] are labeled. [[Subthalamic nucleus]] would be between [[thalamus]] and [[internal capsule]].) |

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BrainInfoNumber = 206 |

MeshName = Basal+Ganglia |

MeshNumber = A08.186.211.730.885.105 |

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The '''basal ganglia''' constitute one major subcortical system of the brain associated with motor and [[learning]] functions.

==History==

The first [[anatomy|anatomical]] identification of distinct subcortical structures was published by the [[English people|English]] anatomist [[Thomas Willis]] in [[1664]]. For a long period, the term corpus striatum was covering a lot of subcortical elements, some of which later discovered to have no links. For a long period also, the putamen and the caudate nucleus were not linked together. In spite of a completely different structure, the putamen was linked to the pallidum in the (inhomogeneous and no more considered) "nucleus lenticularis" (see lentiform fig.). The separation of the striatum into a caudate and a putaminal element is due to the huge increase of the internal capsule in primates. The Vogts simplified the description in proposing the term striatum (neutral adjective) for the set made up of the caudate nucleus, the putamen and the mass linking them ventrally, the fundus. Wilson (1914) described the radiating "pencils" (dense fascicles of striato-pallido-nigral axons) that give its striate aspect (and its name) to the striatum . The striatum is a single mass everywhere made up of the same elements that will be analysed later, having a toric geometry . The link of the striatum with its primary targets, the pallidum and the substantia nigra was soon discovered. This constitutes, with the huge (in number of neurons) striato-pallido-nigral bundle, the basal ganglia core. When crossing the internal capsule this form the comb bundle of Edinger. To this core have been added first the "body of Luys" (1865) (nucleus of Luys on the figure) or subthalamic nucleus, whose lesion was known to produce hemiballism. To this have been recently added other regulators (of the core), the central complex (centre-médian parafascicular) and the pedunculopontine complex.

At the beginning of the 20th century, the basal ganglia system was associated with motor functions, as lesions of these areas would often result in disordered movement in humans (chorea, athetosis, Parkinson disease).

== New logo ==

==Anatomical subdivisions==

As said above the basal ganglia system of the [[primate]] may be subdivided into subsystems.

*A- It starts with the huge '''cortico-striatal connection'''. This, along with the corticospinal, corticopontine, corticothalamic connections, represents a noticeable part of the cortical output. Almost every part of the cortex starting from pyramid cells from the Vth layer send axons to the striatum (except for the primary visual and auditory cortex).

*B-The main part of the basal ganglia system is the '''basal ganglia core'''. This comprises the striatum and its direct targets reached through the striato-pallido-nigral bundle, the two nuclei of the pallidum and the substantia nigra.

-The '''striatum''' is a huge neuronal mass located close to the cerebral ventricles. It is everywhere composed of the same neuronal constituants. In primate, there are 4 neuronal genera: spiny (96%), leptodendritic (2%), spidery (1%) neurons and microneurons(1%) (Yelnik et al 1991). The dendritic arborisations of the spiny neurons are spherical. Their diameter depends on the animal species. Spines are of the same type than those of two other (telencephalic) acanthodendritic (acanthos means spine) genera, the pyramidal neurons of the cerebral cortex and the spiny neurons of the amygdala. Most of these spines synapse with cortical afferents.Their axons have abundant and dense initial axonal collateral then they constitute the striato-pallido-nigral bundle. They are GABAergic. The leptodendritic neurons (or Deiter's) have all the morphological properties of the pallidal neurons. The spidery neurons are specific to primates. They have a big soma and short dendritic and axonal branches. They are the cholinegic neurons of the primate, with a morphology thus entirely different from that of the cholinegic neurons of non-primates. They are the "tonically active neurons" or TANS of Kimura and collaborators. The micro neurons are local circuit neurons similar to those found in the thalamus for instance. They are GABAergic. Some may be dopaminergic (Rochette et al.). The distribution of these neurons is assessed to be biphasic either in the matrix or in striosomes. This opposition is not clear everywhere. In opposition to the head of the caudate, every striatal part has not distinct striosomes. These would represent insular segregation of orbitofrontal axonal endings. They have no relation in macaques with amygdalar afferents. The long oblique split of the striatum by the internal capsule creates the classic division into putamen, caudate and fundus, that are known today not to correspond exactly with the presently accepted anatomofunctional subdivision of the striatum. Due to a separation of corticostriate territories, a sensorimotor territory (or sensorimotor striatum) may be distinguish. It receives axons from the central region of the cortex, primary somatosensory, motor, premotor, accessory motor and anterior parietal. It is essentially putaminal but does no cover the total extent of the putamen. Conversely it includes intracapsular fringes and the inferolateral border of the caudate. To this is opposed an associative territory. This is essentially caudate above all orally and dorsally but does not cover the entire caudate volume. The separation between the two may be clearcut and observe using calbinding immunochemistry (the sensorimotor territory being negative). The isolation of a third ventral striatal part is more difficult.

*The striato-pallido-nigral bundle. This is made up of very numerous thin, fewly myelinated axons . There have been historical and recent dispute concerning the fact that each striatal axon had or not a single target. This has been recently resoluted by Parent et al.. Striatal neurons in primates may have several targets. A non negligeable number of them send axonal termination to all the three targets.The main mediator is GABA but there is one (or several) comediator that vries depending on the target. This is the case for enkephalin in the lateral nucleus of the pallidum and substance P in the medial. The substantia nigra receives a mixture of the two. This would mean that a single axon is able to different parts according to the target. This considerably modifies several decades old schemes.

I changed the logo here to a larger, slightly more professional one. The old logo was meant to be displayed as part of the WGN Radio site's design on a blue background. The text was slanted and difficult to read. This one is all straight and, as I said, a bit more professional.[[User:Tflynn17|Tflynn17]] 15:55, 13 July 2006 (UTC)

* external segment of the [[globus pallidus]] (GPe)

* internal segment of the globus pallidus (GPi)

* [[subthalamic nucleus]] (STN)

* [[substantia nigra]] (SN)

** pars compacta (SNc)

** pars reticulata (SNr)

** pars lateralis (SNl)

Images show two schematic [[Anatomical terms of ___location|coronal]] cross-sections of the [[human]] brain with nuclei of the basal ganglia labeled on the right side.

As it refers to a group of nuclei, the term "basal ganglia" is plural (the singular of ganglia is ''[[ganglion]]''). However this is a [[misnomer]], as “ganglion” refers to a [[soma (biology)|somatic]] cluster within the [[peripheral nervous system]], whereas the basal ganglia are within the [[central nervous system]] (CNS). A somatic cluster within the CNS is referred to as a nucleus, so some [[neuroanatomy|neuroanatomists]] refer to the basal ganglia as the “basal nuclei”.

There are two sets of basal ganglia in the mammalian brain, mirrored in the left and right hemispheres. Two coronal sections are used to show the basal ganglia; the STN and substantia nigra lie deeper back in the brain (more [[Anatomical terms of ___location|caudal]]).

==Evolution and naming==

"Basal ganglia"-like areas are found in the central nervous systems of many species. The striatal and pallidal components can be clearly identified in all [[amniote]]s (mammals, birds, and reptiles) and [[amphibian]]s. The anatomical connections of these nuclei and their [[pharmacology]] also appear relatively conserved. Non-[[tetrapod]] vertebrates such as fish also display basal ganglia-like structures, although the data are less clear in this case.

The basal ganglia system is highly evolutive. There are differences in connections and even neuronal genera between rodents and monkeys and even in simians between new world and old world monkeys. The "entopenduncular nucleus" in [[rodent]]s is not a direct homologue to the "internal segment of the globus pallidus" of primates . Pathophysiological transfers must thus remain careful.

==Neurotransmitters==

Neurons of the various basal ganglia nuclei use a variety of [[neurotransmitter]]s. The most widely used is the inhibitory transmitter [[GABA]] (connections using GABA are shown in blue in the diagram below). Of particular interest is the neurotransmitter of the pigmented [[substantia nigra]] ''pars compacta'' neurons, called [[dopamine]]. Disruption in the production or transmission of dopamine can lead to serious motor and cognitive deficits (for example, see [[Parkinson's disease]]). The substantia nigra pars compacta (SNc) primarily targets the striatum with this neurotransmitter (shown as the magenta connection in the classic connectivity diagram below), and it is thought to play an important role in learning (see [[Long-term potentiation|LTP]]/[[Long-term depression|LTD]]).

==Connections==

[[Image:basal-ganglia-classic.png|frame|left|Classic

Connectivity Diagram showing glutamatergic pathways as red,

dopaminergic as magenta and GABA pathways as blue]] These nuclei are thought to be connected as shown (left). The striatum is the main (but not the only) input zone for other brain areas to connect to the basal ganglia. Via the striatum, the basal ganglia receives input from the [[Cerebral cortex|cortex]], mainly from the [[motor cortex|motor]] and [[prefrontal cortex|prefrontal]] cortices.

The [[neural network|circuitry]] of the basal ganglia is often divided into two major pathways, the '''direct pathway''' and the '''indirect pathway''':

:* '''Direct pathway''': striatum ^-→ GPi/SNr ^-→ thalamus ⁺→ cortex

:* '''Indirect pathway''': striatum ^-→ GPe ^-→ STN ⁺→ GPi/SNr ^-→ thalamus ⁺→ cortex

Cortical activity that excites cells in the striatum that participate in the direct pathway leads to inhibition of areas of the GPi and SNr, which in turn removes their tonic inhibition from the thalamus. This removal of inhibition by inhibition is called '''disinhibition'''. In contrast, cortical activity that excites the striatal cells in the indirect pathway is thought to inhibit the thalamus. This is due to an odd number of the pathways in the '''indirect pathway''' being inhibition pathways (blue arrows), as opposed to an even number of inhibition pathways in the '''direct pathway'''.

In primates, there is evidence that cells in the striatum that participate in the different pathways also differ in the type of [[dopamine receptor]] they express. Striatal cells in the direct pathway (i.e., that have [[axon|axons]] terminating in the GPi and/or SNr) express the D1 class of dopamine receptor, and cells in the indirect pathway express the D2 class. It is generally thought that the nigral (substantia nigra) dopamine acts on these different receptor types in different ways. Dopamine may inhibit striatal cells that have D2 receptors and excite striatal cells that have D1 recepors, although there is little [[physiology|physiological]] evidence for these effects.

== Function ==

The exact function of the basal ganglia is unknown. Current theories suggest that they are involved in mediating between rival perceptions and/or rival motor actions.

==Disorders linked with the basal ganglia==

* [[Huntington's disease]]

* [[Parkinson's disease]]

* [[Tourette syndrome|Tourette's disorder]]

* [[Obsessive-compulsive disorder]]

* [[Attention-deficit hyperactivity disorder]] (ADHD)

* [[Athymhormic syndrome]] ([[PAP syndrome]])

* [[Cerebral palsy]]: basal ganglia damage during second and third trimester of pregnancy

* [[Tardive dyskinesia]], caused by chronic [[antipsychotic]] treatment

==References==

* Nolte, John, ''The Human Brain: An Introduction to its Functional Anatomy'' (Fifth Edition). (St. Louis: Mosby, Inc., 2002), 464-484. ISBN 0-323-01320-1

* Parent, André, ''Comparative Neurobiology of the Basal Ganglia'' (Wiley, New York, 1986), ISBN 0471803480

* Reynolds, J. et, al., "A cellular mechanism of reward-related learning", ''[[Nature (journal)|Nature]]'' (2001) volume 413, pages 67-70.

* Andrew Gilies, ''[http://www.anc.ed.ac.uk/~anaru/research/history/ A brief history of the basal ganglia]'', retrieved on [[27 June]] [[2005]]

==External links==

* {{BrainInfo|hier|206}}

* {{MeshName|Basal+Ganglia}}

*[http://brainmaps.org/index.php?i=basal%20ganglia High resolution neuroanatomical images of the basal ganglia]

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