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The (or '''basal nuclei''') are a group of .
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
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
Neuroanatomists refer to the basal ganglia as the "basal nuclei".
1
The acceptance that the basal ganglia system constitutes one major cerebral system has been slow to appear.
The first
2005 For many years, the term
Corpus Striatum was used to describe a large group of subcortical elements, some of which were later discovered to be functionally unrelated. Additionally, the
Putamen and the
Caudate Nucleus were not linked together. The putamen was thought to be associated to the
Pallidum in what used to be called the "nucleus lenticularis" (see
Lentiform Nucleus on the fig.).
Pioneering work by Cécile and Oskar Vogt (1941) greatly simplified the description of the basal ganglia by proposing the term
Striatum to describe the group of structures consisting of the caudate nucleus, the putamen and the mass linking them
Ventrally , the
Nucleus Accumbens .
The striatum gets its name from the striated appearance created by radiating dense bundles of striato-pallido-nigral
Axons , described by anatomist Kinnear Wilson as "pencil-like". The anatomical link of the striatum with its primary targets, the
Pallidum and the
Substantia Nigra was later discovered. Together, these structures constitute the striato-pallido-nigral bundle, which is the core of the basal ganglia. This nerve bundle forms the so-called "comb bundle of Edinger" when it crosses the
Internal Capsule .
Additional structures that later became associated with the basal ganglia are the "body of Luys" (1865) (nucleus of Luys on the figure) or
Subthalamic Nucleus , whose lesion was known to produce movement disorders. More recently, other areas such as the
Central Complex (centre médian-parafascicular) and the
Pedunculopontine Complex have been thought to be regulators of the basal ganglia.
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's Disease ).
slices of human brain showing the basal ganglia.
ROSTRAL: (STN),
Substantia Nigra (SN)]]
See Also: Anatomical subdivisions and connections of the basal ganglia
The five individual nuclei that make up the
Primate basal ganglia, along with their major subdivisions, are:
''
Rostral ''
''
Caudal ''
There are 2 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
Caudal ). Images show two schematic
Coronal cross-sections of the
Human brain with nuclei of the basal ganglia labeled on the right side.
Functionally, the basal ganglia consist of a series of circuits, such as skeletomotor, limbic and occulomotor circuits. Each circuit projects to specific nuclei within the basal ganglia and its projections e.g. the skeletomotor circuit projects to the ventral lateral, lateral ventral anterior and centromedian thalamic nuclei.
"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 names given to the various nuclei of the basal ganglia are different in different species:
- For example, the "internal segment of the globus pallidus" in primates is called the "entopenduncular nucleus" in Rodent s.
- The "striatum" and "external segment of the globus pallidus" in primates are called the "paleostriatum augmentatum" and "paleostriatum primitivum" respectively in birds.
A clear emergent issue in comparative anatomy of the basal ganglia is the development of this system through phylogeny as a convergent cortically re-entrant loop in conjunction with the development and expansion of the cortical mantle. There is controversy, however, regarding the extent to which convergent selective processing occurs versus segregated parallel processing within re-entrant closed loops of the basal ganglia. Regardless, the transformation of the basal ganglia into a cortically re-entrant system in mammalian evolution occurs through a re-direction of pallidal (or "paleostriatum primitivum") output from midbrain targets such as the superior colliculus, as occurs in
Sauropsid brain, to specific regions of the ventral thalamus and from there back to specified regions of the cerebral cortex that form a subset of those cortical regions projecting into the striatum. The abrupt rostral re-direction of the pathway from the internal segment of the globus pallidus into the ventral thalamus--via the path of the
Ansa Lenticularis --could be viewed as a footprint of this evolutionary transformation of basal ganglia outflow and targeted influence. The evolutionary emergence of cortical re-entrant systems in the brain has been postulated by
Gerald Edelman as a critical basis for the emergence of primary
Consciousness in the theory of
Neural Darwinism .
pathways as red,
Dopaminergic as magenta and
GABA pathways as blue.]]
Basal ganglia connectivity is illustrated in the figure.
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
Cortex , mainly from the
Motor and
Prefrontal cortices.
The
Circuitry of the basal ganglia is often divided into two major pathways, the ''direct pathway'' and the ''indirect pathway'':
Dopamine from the
Substantia Nigra pars compacta stimulates all of the
Dopamine Receptor s, but because the different pathways express different receptors, and the different receptors have different effects, dopamine serves to activate the direct pathway over the indirect pathway, and thus increase the signal to the thalamus.
The different types of neuron of the basal ganglia biosynthesize different
Neurotransmitter s.
- 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 0-471-80348-0
- 3
