Hypothalamus

The hypothalamus (hypothalamus) forms the lower parts of the intermediate brain and participates in the formation of the bottom of the third ventricle. The hypothalamus includes the visual crossover, the visual tract, the gray hillock with a funnel, and mastoid bodies.

The visual crossover (chiasma opticum) has the form of a transversely lying roller formed by fibers of the optic nerves (the second pair of cranial nerves), partially shifting to the opposite side (forming a cross). This cushion on each side laterally and posteriorly continues into the visual tract (tratus opticus). The visual tract is located medially and posteriorly from the anterior perforated substance, traverses the stem of the brain from the lateral side and ends with two roots in the subcortical centers of vision. The larger lateral root (radix lateralis) approaches the lateral geniculate body, and the thinner medial root (radix medialis) is directed to the upper mound of the midbrain roof.

To the anterior surface of the visual crossover, the terminal plate belonging to the final brain is attached and fused with it. It closes the anterior section of the longitudinal slit of the large brain and consists of a thin layer of gray matter, which in the lateral sections of the plate continues into the substance of the frontal lobes of the hemispheres.

A gray tuber (tuber cinereum), behind which mastoid bodies lie, and on the sides - visual tracts is located behind the visual crossover. The gray hillock passes into the funnel (infundibulum), which connects to the pituitary gland. The walls of the gray hillock are formed by a thin plate of gray matter containing sulfur-tubular nuclei (nuclei tuberales). Co of the side of the cavity of the third ventricle into the region of the gray hillock and further into the funnel a tapering depression of the funnel extends.

The mosaic bodies (corpora mamillaria) are located between the gray hill in front and the rear perforated substance from behind. They have the form of two small, about 0.5 cm in diameter, spherical formations of white color. White matter is located only outside the mastoid. Inside is a gray matter in which the medial and lateral nuclei of the mastoid body are distinguished (nuclei corporis mamillaris mediales et laterales). In the mastoid bodies, the columns of the arch end.

In the hypothalamus, there are three main hypothalamic regions - clusters of groups of nerve cells different in shape and size: anterior (regio hypothalamica anterior), intermediate (regio hypothalamica intermedia) and posterior (regio hypothalamica posterior). The accumulations of nerve cells in these regions form more than 30 nuclei of the hypothalamus.

Nerve cells of the hypothalamus nuclei have the ability to produce a secret (neurosecret), which can be transported to the pituitary gland by the processes of these cells. Such nuclei were called neurosecretory nuclei of the hypothalamus. In the anterior part of the hypothalamus are the supraoptotic (surveillance) nucleus (nucleus supraopticus) and paraventricular nuclei (nuclei paraventriculares). The processes of the cells of these nuclei form a hypothalamic-pituitary bundle, terminating in the posterior lobe of the pituitary gland. Among the group of nuclei in the posterior region of the hypothalamus, the medial and lateral nuclei of the mastoid body (nuclei corporis mamillaris mediales et laterales) and the posterior hypothalamic nucleus (nucleus hypothalamicus posterior) are the largest. To the group of nuclei of the intermediate hypothalamic region belong the lower medial and upper medial hypothalamic nucleus (nuclei hypothalamic ventromediales et dorsomediales), the dorsal hypothalamic nucleus (nucleus hypothalamicus dorsalis), the nucleus of the funnel (nucleus infundibularis), the sulfurobugary nucleus (nuclei tuberales), etc.

The nuclei of the hypothalamus are connected by a rather complicated system of afferent and efferent pathways. Therefore, the hypothalamus has a regulating effect on numerous vegetative functions of the body. Neurosecret nuclei of the hypothalamus can influence the function of glandular cells of the pituitary gland, strengthening or inhibiting the secretion of a number of hormones, which in turn regulate the activity of other endocrine glands.

The presence of the nervous and humoral connections of the hypothalamic nuclei and the pituitary gland allowed them to be combined into the hypothalamic-pituitary system.

Phylogenetic studies have shown that the hypothalamus exists in all chordates, is well developed in amphibians, even more in reptiles and fish. Birds clearly express differentiation of nuclei. In gray mammals, a gray matter reaches the cells, the cells of which differentiate into nuclei and fields. The human hypothalamus is not significantly different from the hypothalamus of higher mammals.

There are a large number of classifications of the nuclei of the hypothalamus. E. Gruntel singled out 15 pairs of cores, W. Le Gros Clark - 16, N. Kuhlenbek - 29. W. Le Gros Clark classification was most widespread. IN Bogolepova (1968), on the basis of the above classifications and taking into account the ontogenesis data, suggests the division of the hypothalamic nuclei into four divisions:

1. anterior, or rostral, department (combining the preoptic region and the anterior group - W. Le Gros Clark) - the preoptic medial and lateral regions, the suprachiasmatic nucleus, the supraoptic nucleus, the paraventricular nucleus, the anterior hypothalamic field;
2. middle medial department - ventromedial nucleus, dorsomedial nucleus, infundibular nucleus, posterior hypothalamic field;
3. middle lateral department - lateral hypothalamic field, lateral hypothalamic nucleus, tuberolateral nucleus, tuberomamillar nucleus, periphoronal nucleus;
4. posterior, or mamillary, department - the medial mamillary nucleus, lateral mamillary nucleus.

The anatomical connections of the hypothalamus also clarify its (functional significance.) Among the most important afferent pathways, we can distinguish the following:

1. a medial fascicle of the forebrain, the lateral part of which connects the hypothalamus with the olfactory bulb and tubercle, the periamigdular region and the hippocampus, and the medial part - with the septum, the diagonal region, the caudate nucleus;
2. the terminal strip from the amygdala to the anterior parts of the hypothalamus;
3. fibers passing through the arch from the hippocampus to the mamillary body;
4. thalamo-, strio- and pallid-hypothalamic connections;
5. from the trunk of the brain - the central pathway;
6. from the cortex of the large hemispheres (orbital, temporal, parietal).

Thus, the leading sources of afferentation are the limbic forebrain and the reticular formation of the brain stem.

Efferent systems of the hypothalamus can also be grouped in three directions:

1. descending systems to the reticular formation and the spinal cord - a periventricular system of fibers ending in the middle brain (longitudinal posterior fasciculus), in the autonomic centers of the caudal trunk and spinal cord, and the mastoid-ligament bundle going from the mamillary bodies to the reticular formation of the midbrain;
2. way to the thalamus from mastoid bodies (mastoid-thalamic fascicle), which are part of a closed functional limbic system;
3. pathways to the pituitary-hypothalamic-pituitary path from paraventricular (10-20% of fibers) and supraoptic (80-90%) nuclei to the posterior and partly middle parts of the pituitary, tuber-pituitary path from the ventromedial and infundibular nuclei to the adenohypophysis.

In the works of J. Ranson (1935) and W. Hess (1930, 1954, 1968) there are data on the dilatation and contraction of the pupil, on the increase and decrease in arterial pressure, on the increase and decrease in the pulse in stimulation of the hypothalamus. On the basis of these studies, the zones providing the sympathetic (posterior part of the hypothalamus), parasympathetic (anterior part) effects were identified, and the hypothalamus itself was considered as the center integrating the activity of the visceral system innervating the organs and tissues. However, with the development of these studies, a large number of somatic effects were also revealed, especially in the free behavior of animals [Gellhorn E., 1948]. O. G. Baklavajan (1969) observed, in some cases, the activation reaction in the cortex of the cerebral hemispheres, the alleviation of the monosynaptic potentials of the spinal cord, the increase in arterial pressure, in others the opposite effect. At the same time, vegetative reactions were the highest threshold. O. Sager (1962), with diathermy of the hypothalamus, found inhibition of the y-system and EEG-synchronization, with excessive heating - the reverse effect. The hypothalamus concept is formed as a brain department that performs interaction between regulatory mechanisms, the integration of somatic and vegetative activity. From this point of view, it is more correct to divide the hypothalamus not into the sympathetic and parasympathetic divisions, but to isolate in it the dynamogenic (ergotropic and trophotropic) zones. This classification has a functional, biological character and reflects the involvement of the hypothalamus in the implementation of holistic acts of behavior. Obviously, not only vegetative, but also somatic system participates in the maintenance of homeostasis. Ergo- and trophotropic zones are located in all parts of the hypothalamus and overlap each other in separate areas. At the same time, it is possible to identify the zones of their "condensation". Thus, trophotropic apparatuses are more clearly represented in the anterior regions (preoptic zone), and ergotrophic apparatuses in the posterior (mamillary bodies). Analysis of the main afferent and efferent connections of the hypothalamus with limbic and reticular systems sheds light on its role in the organization of integrative forms of behavior. The hypothalamus in this system occupies a special - central - position both due to the topographic location in the center of these formations, and as a result of physiological characteristics. The latter is determined by the role of the hypothalamus as a specifically constructed part of the brain, especially sensitive to shifts in the internal environment of the organism, which reacts to the slightest fluctuations in the humoral parameters and forms appropriate behavioral acts in response to these shifts. The special role of the hypothalamus is predetermined by its anatomical and functional proximity to the pituitary gland. The nuclei of the hypothalamus are divided into specific and nonspecific. The former include the structures projected onto the pituitary gland, the rest are other nuclei, the effects of which can be differentiated depending on the strength of the effect. Specific nuclei of the hypothalamus have an unambiguous effect and differ from other brain structures by the ability to neurocrinia. These include the supraoptical, paraventricular and small-cell nuclei of the gray hillock. It has been established that in the supraoptic and paraventricular nuclei an antidiuretic hormone (ADH) is formed, descending along the axons of the hypothalamic-pituitary tract into the posterior lobe of the pituitary gland. Later it was shown that in the neurons of the hypothalamus, releasing factors are formed, which, falling into the adenohypophysis, regulate the secretion of triple hormones: adrenocorticotropic (ACTH), luteinizing (LH), follicle stimulating (FSH), thyrotropic (TSH). The formation zones of the realizing factors for ACTH and TSH are the nuclei of the anterior part of the medial elevation and the preoptic region, and for the THG the posterior parts of the gray hillock. It has been established that hypothalamic-pituitary beams in humans contain about 1 million nerve fibers.

Undoubtedly, other brain departments (medial-basal structures of the temporal region, reticular formation of the brain stem) participate in neuroendocrinal regulation. However, the most specific apparatus is the hypothalamus, which includes endocrine glands in a system of holistic body reactions, in particular, reactions of a stressful nature. Tropho- and ergotrophic systems have at their disposal for the operation not only a peripheral sympathetic and parasympathetic system, but also specific neurohormonal apparatuses. The hypothalamic-pituitary system, functioning on the principle of feedback, is largely self-regulating. The activity of formation of the realizing factors is also determined by the level of hormones in the peripheral blood.

Thus, the hypothalamus is an important part of the limbic and reticular brain systems, however, being included in these systems, it retains its specific "inputs" in the form of a special sensitivity to shifts in the internal environment, as well as specific "exits" through the hypothalamic-pituitary system, paraventricular connections to the vegetative formations lying below, and also through the thalamus and the reticular formation of the brainstem to the cortex and the spinal cord.

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