Basal Ganglia Flashcards
The basal nuclei (or basal ganglia) are large masses of grey matter situated in the cerebral hemispheres.
Anatomically, the basal nuclei include large subcortical masses of grey matter located within each cerebral hemisphere developing from telencephalon. They include:
The caudate nucleus and the lentiform nucleus together constitute the ____(a)____. This consists of two functionally distinct parts. The caudate nucleus and the putamen form one unit called the ____(b)____ (also known as neostriatum), while the globus pallidus forms the other unit, the ____(c)____ (a.k.a paleostriatum). Phylogenetically, the amygdaloid nuclear complex and claustrum are considered as ____(d)____.
Functionally, the basal nuclei comprise of structures, the lesion of which produces dyskinesias (abnormal involuntary purposeless movements). The structures included are:
- Corpus striatum
- The subthalamic nucleus (which is of diencephalic origin) is very closely linked to the basal nuclei and is regarded as belonging to this group.
- The substantia nigra (midbrain) is also closely linked, functionally, to the basal nuclei.
- Some masses of grey matter found just below the corpus striatum (near the anterior perforated substance) are described as the ventral striatum. The part of the globus pallidus, which lies below the level of the anterior commissure, is designated as the ventral pallidum.
Caudate Nucleus Topography
It is a C-shaped mass of grey matter, consisting of a large head, body and thin tail. The nucleus is intimately related to the ____(a)____ ventricle. The head of the nucleus bulges into the anterior horn of the ventricle and forms the greater part of its ____(b)____. The body of the nucleus lies in the floor of the central part and the tail in the roof of the inferior horn of the ventricle.
Caudate Nucleus Topography
The anterior part of the head of the caudate nucleus is fused, inferiorly, with the lentiform nucleus. Fusion of these two results in strands of grey matter passing through the descending fibres of internal capsule giving a striated appearance and hence the name ‘corpus striatum’ to denote caudate and lentiform nuclei. This region of fusion is referred to as the ____(a)____, which is continuous, inferiorly, with the anterior perforated substance. The anterior end of the tail of the caudate nucleus ends by becoming continuous with the ____(b)____ nucleus.
The body of the caudate nucleus lies lateral to the to the ____(a)____ and medially to the ____(b)____, which separates it from the lentiform nucleus.
(a) thalamus
(b) internal capsule
[Diagram]
State the relations of the lentiform nucleus.
Medially: Internal capsule
Laterally: Separated from the claustrum by fibres of the external capsule
NB: these capsules are so called because they appear, to the naked eyes, to form a covering or capsule for the lentiform nucleus
Superiorly: related to corona radiata
Inferiorly: sublentiform part of internal capsule
[Diagram]
In this card, click the answer to link you to photos relating corpus striatum to the internal capsule.
State the afferent connections of corpus striatum.
- The entire cerebral cortex via corticostriate fibres. These fibres are glutamatergic.
- The intralaminar nuclei of the thalamus via thalamostriate fibres
- The pars compacta of the substantia nigra via nigrostriate fibres. These fibres are dopaminergic.
- Noradrenergic fibres are received from the locus coeruleus.
- Serotoninergic fibres are received from the raphe nuclei (in the reticular formation of the midbrain).
The main output of the corpus striatum is concentrated upon the pallidum and on the substantia nigra (pars reticularis). The outflow from globus pallidus forms four separate bundles. State these bundles.
~ Fasciculus lenticularis: it connects the globus pallidus internus to the thalamus and is a part of the thalamic fasciculus.
~ Ansa lenticularis arises from both the inner and outer segments of the globus pallidus and enters the subthalamic region where it meets the dentatorubrothalamic fibres and the fasciculus lenticularis. The union of the three tracts is called the thalamic fasciculus, which terminates in the ventral anterior (VA), ventral lateral (VL) and centromedian nuclei of thalamus [which then project to the motor and premotor areas of the cerebral cortex].
~ Subthalamic fasciculus consists of reciprocal connections between the globus pallidus and the subthalamic nucleus.
~ Some fibres from globus pallidus also pass to the substantia nigra (pallidonigral fibres).
~ [Diagram: afferent and efferent connections of the basal ganglia]
~ [Diagram: basal ganglia]
State the functions of the corpus striatum.
- It mediates enormous number of automatic activities involved in normal motor functions e.g. the maintenance of erect posture when sitting or standing.
- It helps in smoothening the voluntary motor activity of the body.
- It helps in maintenance of muscle tone.
- It helps in prevention of involuntary movement.
What is the claustrum?
This is a thin lamina of grey matter that lies lateral to the lentiform nucleus. It is separated from the latter by fibres of the external capsule. Laterally, it is separated by a thin layer of white matter from the cortex of the insula. It is functionally related probably to limbic system. [Diagram]
The thin strip of white matter between the putamen and claustrum is called the ____(a)____, and the white matter separating the claustrum from the insular cortex is the ____(b)____.
(a) external capsule
(b) extreme capsule
[Diagram]
What is the amygdaloid nuclear complex/amygdaloid body/amygdala?
It lies in the temporal lobe of the cerebral hemisphere and close to the temporal pole. It lies deep to the uncus and is related to the anterior end of the inferior horn of the lateral ventricle. It is functionally related to limbic system.
State the connections of substantia nigra.
- The pars compacta of the substantia nigra sends a dopaminergic projection to the striatum (remember striatum is comprised of caudate nucleus and putamen).
- The pars reticularis projects to the ventral anterior nucleus of the thalamus. These impulses are relayed to frontal lobe of the cerebral cortex.
- Other efferents of the pars reticularis reach the reticular formation of the medulla and to the spinal cord.