Human Anatomy, Part 2 - K. A. Diubenko, A. K. Kolomiitsev, Yu. B. Chaikovskyi 2008

Special Part
Nervous system, systema nervosum - Special Part
Brain - Telencephalon - Basal nuclei

The basal nuclei, nuclei basales, or subcortical nuclei, nuclei subcorticales, (often referred to as the subcortex) are collections of Gray matter within the cerebral hemispheres (Fig. 156). They participate in adjusting the program of complex motor acts (mediating myostatic reactions and optimally redistributing Muscle tone) and in shaping emotional-affective responses. Three pairs of subcortical nuclei are distinguished: the corpus striatum, corpus striatum, the amygdaloid body, corpus amygdaloideum, and the claustrum, claustrum. The basal nuclei also include a complex of nuclei located between the anterior perforated substance (substantia perforata anterior) and the anterior part of the globus pallidus (globus pallidus), which belong to the septal area. The corpus striatum*, corpus striatum, is formed by two nuclei: the caudate Nucleus, nucleus caudatus, which is a pear-shaped Structure that arches around the thalamus, and the lentiform nucleus, nucleus lentiformis. The anterior portion of the caudate nucleus has a thickening called the HEAD, caput nuclei caudati, the middle portion forms the body of the caudate nucleus, corpus nuclei caudati. The body continues into the tail, cauda nuclei caudati.

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Fig. 156. Basal nuclei, nuclei basales (horizontal section of the Brain at the level of the commissure of the fornix)

* The corpus striatum gets its name from the fact that on horizontal sections it has the appearance of alternating bands of gray and White matter.

The head of the caudate nucleus is located in the anterior part of the hemisphere and projects into the anterior horn of the lateral ventricle, cornu anterius ventriculi lateralis, forming its floor and lateral wall. The body of the caudate nucleus bounds the lateral side of the central part of the lateral ventricle, pars centralis ventriculi lateralis. The thin posterior end of the caudate nucleus, which participates in forming the roof of the inferior horn of the lateral ventricle, forms the tail of the caudate nucleus, cauda nuclei caudati. The lateral surface of the caudate nucleus lies adjacent to the internal capsule, and its medial border is adjacent to the stria terminalis.

Functions of the corpus striatum:

1. The corpus striatum exerts a dual effect on the globus pallidus—inhibitory and excitatory, with the inhibitory effect predominating.

2. Neurons of the corpus striatum exert an inhibitory effect on the neurons of the substantia nigra.

3. The corpus striatum exerts an inhibitory effect on the motor cortex (O. S. Andrianov, 1980).

The lentiform nucleus, nucleus lentiformis, resembles a wedge in shape, with its base directed laterally and its apex medially and downward. It is located laterally and slightly below the caudate nucleus and the thalamus, from which it is separated by the internal capsule. Anteriorly and ventrally, the lentiform nucleus connects with the head of the caudate nucleus by thin bands of gray matter. Its lateral surface is slightly convex, oriented vertically, and borders the external capsule, capsula externa, which is a thin medullary lamina bounded laterally by a layer of gray matter—the claustrum, claustrum. The ventral surface of the lentiform nucleus lies horizontally and, in its middle portion, connects with the cortex in the region of the anterior perforated substance. The lentiform nucleus is divided into three parts: the dark lateral portion—the putamen, putamen, and two light-colored medial portions—the globus pallidus, globus pallidus.

The caudate and lentiform nuclei belong to the Components of the extrapyramidal system and execute complex unconditioned reflex movements. The caudate nucleus controls many general movements. The caudate nucleus and the putamen, together with the Cerebral Cortex, control the pattern of movements, while the globus pallidus controls the execution of movements.

Damage to the caudate nucleus results in a Clinical presentation dominated by involuntary movements (hyperkinesias). The patient is unable to control their Muscles.

The claustrum, claustrum, is a thin sheet of gray matter located in the WHITE MATTER OF the hemispheres, separating the putamen from the insular cortex. The white matter separating the claustrum and the putamen is called the external capsule, capsula externa, and the area of white matter between the claustrum and the insular cortex is called the extreme capsule, capsula extrema. The function of the claustrum remains unknown.

The amygdaloid body, corpus amygdaloideum, is a complex of nuclei located primarily in the region of the uncus of the parahippocampal gyrus. These nuclei differ from each other cytologically and cytoarchitectonically and are morphologically grouped as the amygdaloid* area. It is situated in the anterior part of the temporal lobe. The amygdaloid body is a subcortical olfactory center, has a complex structure, and belongs to the limbic system. Experiments on the limbic system of monkeys and other animals indicate that the amygdaloid body assumes most of the functions in controlling general behavior. The amygdaloid body influences behavior and activity based on the internal needs of the Organism: nutritional needs, sexual interest, and the expression of anger.

According to the latest nomenclature, the amygdaloid body, or complex, is divided into four fields and eight nuclei. In neurosurgical practice, the Classification of the nuclei of the amygdaloid area proposed by Brockhaus (H. Brockhaus) is widely used.

According to this classification, the cortical Nucleus of the amygdaloid area is called the superficial periamygdaloid nucleus, the medial is the superficial supra-amygdaloid, and the lateral is the lateral deep; the lateral part of the basal nucleus is the intermediate deep; the medial part of the basal nucleus is the ventral deep, and the accessory basal nucleus is the medial deep. This classification is most fully presented in the stereotaxic atlas of the human brain (G. Schaltenbrand, P. Bailey, 1959).

Connections of the Basal Nuclei

The basal nuclei have numerous connections with other brain structures (Fig. 157). Through these pathways, they help control subconscious movements.

The corpus striatum receives afferent fibers from the thalamus, from the nuclei of the Hypothalamus that border the Third ventricle, from the Midbrain tegmentum, and from the substantia nigra. These fibers terminate near the small Cells of the corpus striatum, from which axons predominantly reach the large cells and then project to the pallidum as part of the striopallidal tract, fasciculus striopallidaris.

Fibers from the caudate nucleus cross the internal capsule, enter the putamen, and then penetrate the medullary lamina to enter the pallidum.

Efferent fibers of the basal nuclei originate from the globus pallidus. The main efferent bundle is the ansa lenticularis, ansa lenticularis. Its fibers originate in the caudate nucleus and participate in forming the medullary laminae, laminae medullares. The loop synapses in the globus pallidus. Fibers emerging from the globus pallidus cross the internal capsule, and at the boundary with the hypothalamus, they fan out and terminate in the anterior and lateral nuclei of the thalamus, the hypothalamus, the substantia nigra, the subthalamic nucleus, nucleus subthalamicus, and the red nucleus. Some fibers travel within the anterior tegmental decussation (decussatio tegmentalis anterior) to the contralateral side, where they terminate in the corresponding structures.

The second bundle emerging from the globus pallidus—the lenticular fasciculus, fasciculus lenticularis—is located beneath the zona incerta and includes fibers projecting to the subthalamic nucleus, nucleus subthalamicus, the thalamus, the red nucleus, the inferior olivary nucleus, the reticular formation, the corpora quadrigemina, lamina tecti, and the periventricular nuclei. Some fibers cross to the contralateral side via the anterior tegmental decussation and terminate in the same structures.

* amygdaloideus from Latin - almond-shaped; syn.: amygdaloid body, corpus amygdaloideum, amygdaloid nucleus, nucleus amygdalae

Fig. 157. Diagram of the connections of the basal nuclei with brain structures (after C. and O. Vogt)

The Basal Ganglia are characterized by extensive connections with the motor and premotor areas of the cerebral cortex, the limbic system, and the Cerebellum. This wide range of connections accounts for the complex Functional Significance of the basal ganglia (integrated into the striopallidal system) in various neurophysiological and psychophysiological processes (N. P. Bekhtereva, 1971).