Basal nuclei (Basal Ganglia)

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Basal Nuclei (Basal Ganglia)


The basal ganglia are the large masses of grey matter situated within the white core of each cerebral hemisphere and form essential constituents of the extrapyramidal system. The basal ganglia are now recognized as basal nuclei, but the former term is still commonly used.


Anatomically, the term basal ganglia include:



Functionally, the term basal ganglia also include substantia nigra and subthalamus. Some workers also include red nucleus.


The basal nuclei are important in organizing and coordinating somatic motor activities especially willed movements. They are also involved in automatic stereotyped postural and reflex motor activities such as normal individuals swing their arms when they walk.



Corpus Striatum


The corpus striatum is situated lateral to the thalamus. Topographically it is almost completely divided into the caudate nucleus and the lentiform nucleus by a band of nerve fibres, the internal capsule. However, anteroinferior ends of these nuclei remain connected by a few bands of grey matter across the anterior limb of internal capsule. These bands give it a striated appearance, hence the name corpus striatum (Figs 13.1–13.3).





The lentiform nucleus consists of two parts: a darker lateral part putamen and a medial paler part globus pallidus.


Phylogenetically corpus striatum forms two distinct functional units, the paleostriatum and the neostriatum.


The globus pallidus is relatively ancient and termed paleostriatum/pallidum. The caudate nucleus and putamen being recent in development, together form the neostriatum/ striatum. The striatum is largely afferent whereas pallidum is largely efferent structure.


These features of corpus striatum may be summarized as follows:



image




Caudate Nucleus


Caudate nucleus is a large comma-shaped mass of grey matter, which surrounds the thalamus and is itself surrounded by the lateral ventricle (Fig. 13.4). Its whole length of convexity projects into the cavity of lateral ventricle.



Its rounded anterior part in front of interventricular foramen is called its head. The head gradually and imperceptibly tapers caudally into the body and then into a tail which merges at its anterior extremity with an almond-shaped mass of grey matter called amygdaloid body (Fig. 13.2).


The head is large and rounded, and forms the floor and lateral wall of the anterior horn of lateral ventricle. The bands of grey matter connect it to the putamen across the anterior limb of internal capsule (Fig. 13.3).


The body is long and narrow, and forms the floor of the central part of lateral ventricle. It is separated from thalamus by stria terminalis and thalamostriate vein.


The tail is long and slender, and forms the roof of inferior horn of lateral ventricle. It terminates anteriorly (topographically) in the amygdaloid body.



Lentiform Nucleus


Lentiform nucleus is a large lens-shaped (biconvex) mass of grey matter beneath the insula forming the lateral boundary of internal capsule. In horizontal section of cerebrum, it appears wedge-shaped with broad convex base directed laterally.


It has three surfaces and divides into two parts:





Connections of corpus striatum (Fig. 13.5)


The striatum (caudate nucleus and putamen) is the receptive part while globus pallidus is the efferent part (outflow centre) of the corpus striatum.




Afferent connections


The striatum receives afferents chiefly from cerebral cortex, thalamus and substantia nigra.



Jan 2, 2017 | Posted by in NEUROLOGY | Comments Off on Basal nuclei (Basal Ganglia)
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