Subcortical parts of the brain (subcortex)

The subcortical regions of the brain include the thalamus, basal ganglia at the base of the brain (caudate nucleus, lenticular nucleus consisting of the putamen, lateral and medial globus pallidus); white matter of the brain (centrum semiovale) and internal capsule, as well as the hypothalamus. Pathological processes (hemorrhage, ischemia, tumors, etc.) often develop simultaneously in several of the listed formations, but it is also possible to involve only one of them (completely or partially).

Thalamus (optic thalamus). An important subcortical section of the afferent systems; the conduction pathways of all types of sensitivity are interrupted in it. The cortical sections of all analyzers also have feedback connections with the thalamus. Afferent and efferent systems ensure interaction with the cortex of the cerebral hemispheres. The thalamus consists of numerous nuclei (there are about 150 of them in total), which are combined into groups that differ in their structure and function (anterior, medial, ventral and posterior groups of nuclei).

Thus, three main functional groups of nuclei can be distinguished in the thalamus.

1. A complex of specific or relay thalamic nuclei through which afferent impulses of a certain modality are conducted. These nuclei include the anterior-dorsal and anterior-ventral nuclei, a group of ventral nuclei, the lateral and medial geniculate bodies, and the frenulum.
2. Non-specific thalamic nuclei are not associated with the conduction of afferent impulses of any particular modality. The neuronal connections of the nuclei are projected in the cerebral cortex more diffusely than the connections of specific nuclei. Non-specific nuclei include: the midline nuclei and adjacent structures (medial, submedial, and medial central nuclei); the medial part of the ventral nucleus, the medial part of the anterior nucleus, the intralaminar nuclei (paracentral, lateral central, parafascicular, and central median nuclei); the nuclei lying in the paralaminar part (dorsal medial nucleus, anterior ventral nucleus), as well as the reticular complex of the thalamus,
3. The associative nuclei of the thalamus are those nuclei that receive stimulation from other nuclei of the thalamus and transmit these influences to the associative areas of the cerebral cortex. These formations of the thalamus include the dorsal medial nucleus, the lateral group of nuclei, and the thalamic cushion.

The thalamus has numerous connections with other parts of the brain. The corticothalamic connections form the so-called thalamic peduncles. The anterior peduncle of the thalamus is formed by fibers connecting the thalamus with the frontal cortex. Pathways from the frontoparietal region go to the thalamus through the superior or middle peduncle. The posterior peduncle of the thalamus is formed by fibers coming from the cushion and lateral geniculate body to area 17, as well as the temporothalamic bundle connecting the cushion with the cortex of the temporo-occipital region. The inferior-internal peduncle consists of fibers connecting the cortex of the temporal region with the thalamus. The subthalamic nucleus (Lewis's body) belongs to the subthalamic region of the diencephalon. It consists of uniform multipolar cells. The Forel areas and the indefinite zone (zona incetta) also belong to the subthalamic region. The ^H1 Forel field is located under the thalamus and includes fibers connecting the hypothalamus with the striatum - fasciculis thalami. Under the H1 Forel field ^{is the indefinite zone, which passes into the periventricular zone of the ventricle. Under the indefinite zone lies theH2} Forel field, or fasciculus lenticularis, which connects the globus pallidus with the subthalamic nucleus and periventricular nuclei of the hypothalamus.

The hypothalamus (subthalamus) includes the leash with the commissure, the epithalamic commissure and the pineal gland. In the trigonum habenulae is located the gangl, habenulae, in which two nuclei are distinguished: the internal, consisting of small cells, and the external, in which large cells predominate.

Lesions of the thalamus cause primarily disturbances of cutaneous and deep sensitivity. Hemianesthesia (or hypoesthesia) of all types of sensitivity occurs: pain, thermal, joint-muscular and tactile, more in the distal parts of the extremities. Hemihypesthesia is often combined with hyperpathy. Lesions of the thalamus (especially its medial parts) can be accompanied by intense pain - hemialgia (painful sensations of a log, burning) and various vegetative-cutaneous disorders.

A gross violation of the joint-muscle sense, as well as a violation of the cerebellar-thalamic connections, cause the appearance of ataxia, which is usually of a mixed nature (sensory and cerebellar).

The consequence of damage to the subcortical parts of the visual analyzer (lateral geniculate bodies, thalamic cushion) explains the occurrence of hemianopsia - loss of opposite halves of the visual fields.

When the thalamus is damaged, the disruption of its connections with the striopallidal system and extrapyramidal fields of the cortex (mainly the frontal lobes) can cause movement disorders, in particular complex hyperkinesis - choreic athetosis. A peculiar extrapyramidal disorder is the position of the hand; it is bent at the wrist, brought to the ulnar side, and the fingers are extended and pressed to each other (thalamic hand, or "obstetrician's hand"). The functions of the thalamus are closely related to the emotional sphere, therefore, when it is damaged, forced laughter, crying and other emotional disorders can occur. Often, with half damage, paresis of the facial muscles can be observed on the side opposite the lesion, which is revealed during movements on a task (mimic paresis of the facial muscles). The most constant thalamic hemisyndromes include hemianesthesia with hyperpathy, hemianopsia, and hemiataxia.

Dejerine-Roussy tapamic syndrome: hemianesthesia, sensory hemi-ataxia, homonymous hemianopsia, hemialgia, "thalamic hand", vegetative-trophic disorders on the side opposite the lesion, forced laughter and crying.

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