BASAL GANGLIA LÀ GÌ

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The basal ganglia consists of a number of subcortical nuclei. The grouping of these nuclei is related to function rather than anatomy – its components are not part of a single anatomical unit, và are spread deep within the brain.

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It is part of a basic feedbaông chồng circuit, receiving information from several sources including the cerebral cortex. The basal ganglia feeds this information back lớn the cortex, via the thalamus. In doing so, it acts khổng lồ modulate and refine cortical activity – such as that controlling descending motor pathways.

Although widely used, the term basal ganglia is a misnomer, as ganglia are collection of cell bodies outside of the central nervous system. Since a collection of subcortical cell bodies inside the nervous system are known as nuclei, the name basal nuclei is more accurate.

Nuclei of the Basal Ganglia

The anatomy of the basal ganglia is complex since it is spread throughout the forebrain.

Its components can be divided into input đầu vào nuclei, output nuclei & intrinsic nuclei. Input nuclei receive sầu information, which is then relayed lớn intrinsic nuclei for processing, & further passed lớn output nuclei:

Input NucleiIntrinsic Nucleiđầu ra Nuclei
Caudate nucleus & putamen (neostriatum)External globus pallidusSubthalamic nucleusPars compacta of the substantia nigraInternal globus pallidusPars reticulata of the substantia nigra

In the telencephalon, the caudate nucleus (CN) and the putamen (Pu) are collectively called neostriatum, & their functions are closely related. The most rostral aspect of the neostriatum, where the caudate nucleus và the putamen join together, is termed nucleus accumbens (Acb), which is part of a functionally separate domain named ventral striatum.

The globus pallidus is divided in an external (GPe) và an internal (GPi) domains, which are functionally different

The subthalamic nucleus (StN) lies in the diencephalon. In the mesencephalon, the substantia nigra is divided into lớn two parts; the pars compacta (SNc) and the pars reticularis (SNr).

Caudate Nucleus

The caudate nucleus forms the lateral wall of the lateral ventricle & follows the telencephalic expansion during development. It has a characteristic ventricular C-shape when fully developed.

It can be identified as the collection of gray matter on the wall of the lateral ventricles. During development, the caudate nucleus is separated from the putamen by descending Trắng matter fibres, which at this màn chơi are known as internal capsule.

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Fig 1 – Coronal section. Note the relationship of the caudate nucleus to lớn the lateral wall of the lateral ventricle

Lentiform Nucleus (Globus Pallidus and Putamen)

The lentikhung nucleus is comprised of globus pallidus and the putamen. Although anatomically related, they share no functional relationship. It can be identified as a collection of gray matter laying deep within the hemispheres.

The putamen forms the lateral aspect of the lentiform nucleus. On its concave sầu inner surface lies the most exterior of the globus pallidus, the GPe, & the most internal structure is the GPi. The putamen is separated from the GPe by the lateral medullary lamimãng cầu, và the medial medullary lamina separates the GPe from the GPi

cảnh báo that, laterally to the putamen, there is another collection of white matter fibres known as external capsule. A thin bundle of grey matter can be seen lateral to lớn the external capsule: this is the claustrum, once thought to lớn be part of the basal ganglia. More lateral khổng lồ the claustrum is the extreme capsule, which are trắng matter tracts separating the claustrum from the neocortical insula.

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Substantia Nigra

The substantia nigra is conspicuous in gross specimens and can be seen in cuts through the midbrain, having a dark appearance due lớn the neuromelanin present in the cells of the SNc.

Subthalamic Nucleus

The subthalamic nucleus, as the name implies, lies inferior lớn the thalamus, and right above the substantia nigra.

Function

In simple terms, the basal ganglia provide a feedbachồng mechanism to the cerebral cortex, modulating and refining cortical activation.

Its main function is related lớn motor refinement, acting as a tonically active sầu break, preventing unwanted movements to start. Much of this involves reducing the excitatory input to lớn the cerebral cortex. This prevents excessive sầu và exaggerated movements.

The basal ganglia also plays an important role in modulating cognitive and emotional responses. The putamen receives almost exclusive sầu inputs from motor and somatosensory cortices và projects baông xã to motor areas, and is thus related khổng lồ the motor loop. The caudate nucleus receives input from cortical association areas & projects lớn prefrontal areas. In contrast, the ventral striatum (including the Acb) receives limbic inputs and is thus related lớn emotions.

Vasculature

The arterial supply to the basal ganglia comes mainly from the middle cerebral artery, a continuation of the internal carotid artery.

The main artery is named lenticulostriate artery và, as the name implies, provides most of the circulation to lớn the striatum & the lenticular nucleus.

There is also a small amount of supply from the anterior cerebral artery và the anterior choroidal artery, both of which are also branches of the internal carotid artery, supplying the more anterior aspect of the ganglia, (i.e. the head of the caudate nucleus & the nucleus accumbens). This particularly large artery is referred khổng lồ as medial striate artery (of Heubner).

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The substantia nigra & the subthalamic nucleus are more posterior và thus receive sầu its vasculature from branches of the posterior cerebral & posterior communicating arteries.