DIENCEPHALON [diencephalon (PNA, JNA, BNA); synonym interstitial brain)] — the department of a brain located between final and a mesencephalon. The item of m — the largest part of a brain trunk including a thalamus (a visual hillock), a hypothalamus (hypothalamus), a metathalamus (a zabugorye, foreign area) and an epithalamus (nadbugorye).
Comparative anatomy and embryology. The most ancient education of P. of m is the hypothalamus. The relevant structures of a brain exist at all chordates. At cyclostomous P. the m is subdivided into an epithalamus, dorsal and ventral thalamuses and a hypothalamus. The last considerably surpasses other departments of P. of m in size. Cyclostoma have rudiments of a lateral cranked body. Development of a thalamus begins at amphibians. At reptiles the thalamus prevails in size over a hypothalamus. At mammals the thalamus reaches the highest development.
In the field of a roof P, the m at the lowest vertebrata is observed a number of protrusions: paraphysises, dorsal bag, parapineal (front parietal) and pineal (back parietal) bodies. At a lamprey front and back parietal bodies are receptor and support the structures reminding structures of an eye. They are connected by fibers with kernels of a lead. At amphibians the front parietal body in the course of embryonic development is displaced kzad and turns into gland — a pinus (epiphysis) — located between back commissure and back parietal body (a parietal eye) which by the end of the embryonal period is reduced. At some reptiles, as well as at Cyclostoma, an unpaired parietal eye remains during all life. At mammals the front parietal body disappears, and from a proximal part (back parietal body) the pinus (corpus pineale) develops.
At the person P. of m it is formed of back department of a front brain bubble (prosencephalon). As a result of the uneven growth of a bubble from its sidewalls pair education — a thalamus develops, in upper (dorsal) part of a bubble the pinus and an upper wall of the third ventricle form. The lower (ventral) wall forms unpaired protrusion — a funnel, from the distal end the cut develops a back share of a hypophysis — a neurohypophysis. All these educations limit the cavity of a brain bubble turning into the third ventricle. At a three-months fruit two superficial grooves divide P. of m into 3 departments: upper — an epithalamus, average — a thalamus, lower — a hypothalamus. In the subsequent there is a further differentiation of structures of P. of m, isolation of its elements that leads to allocation of the fourth (back) department of P. of m — a metathalamus. By the end of the 5th month of pre-natal development as a result of concentration of nervous cells in a thalamus separate kernels begin to be formed. Newborns have kernels of a thalamus and a hypothalamus are already differentiated in the cytovery tectonic relation, and myelination of nerve fibrils continues also in the post-natal period.
Thalamus (thalamus) — the pair formation of an ovoid form which is located on both sides from the third ventricle (fig. 1). Represents massive accumulation of the gray matter divided by layers of white matter (brain plates) into separate kernels. From above thalamus (see) it is covered with the arch and a corpus collosum (see), from below adjoins a hypothalamus. The front made narrower end of a thalamus comes to an end with a front hillock (tuberculum ant. thalami), the back end is expanded and is called a pillow (pulvinar).
Hypothalamus (hypothalamus) — part P. of m located under a thalamus and delimited from the last by a hypothalamic furrow (sulcus hypothalamicus) following from an interventricular foramen to an opening of a water supply system of a mesencephalon (see fig. 1 to St. Hypothalamus ). On the basis of a brain the front border of a hypothalamus is made by a first line of visual decussation, back — the rear edges of mamillary bodies, or mastoidal, bodies (corpora mamillaria), lateral — the outer edges of visual tracts. Visual decussation (chiasma opticum), a visual tract (tractus opticus), a gray hillock (tuber cinereum), a funnel (infundibulum), a back share are a part of a hypothalamus hypophysis (see) — a neurohypophysis (neurohypophysis), mamillary bodies (see). Gray matter of a hypothalamus forms apprx. 32 couples of kernels which are located in a lower part of an outside wall and in the field of a bottom of the third ventricle.
Metathalamus (metathalamus) is behind a thalamus, consists of two steam rooms (medial and lateral) cranked bodies (corpus geniculatum mediale et laterale) representing oblong and oval hillocks (fig. 2) of white color into whom the kernels of the same name are put (nuclei corporis geniculati lat. et med.). The lateral cranked body is larger medial, but more flat. It is located on a nizhnelateralny surface of a pillow of a thalamus. The medial cranked body lies under a pillow of a thalamus. It is delimited from a pillow and legs of a brain is clear the expressed furrow. In the cells forming a kernel of a medial cranked body fibers of a lateral (acoustical) loop reach a limit (lemniscus lat.). Fibers from cells of this kernel, a cut is the subcrustal center of an acoustical way, go as a part of acoustical radiance (radiatio acustica) and come to an end in bark of an upper temporal crinkle (see. Acoustical centers, ways ). In cells of a lateral cranked body fibers of a lateral root of a visual tract reach a limit. Shoots of these cells together with fibers from a pillow of a thalamus form visual radiance (radiatio optica), edges comes to an end in a cerebral cortex in the field of a shporny furrow (see. Visual centers, ways ).
Epithalamus (epithalamus) is located over a thalamus and consists of a pinus (see), leads (habenulae), triangles of leads (trigona habenularum), epitalamichesky (back) commissure [commissura epithalamica (posterior)]. A pinus — the unpaired gland of an oval form located over upper hillocks of a roof of a mesencephalon. Plates of marrow depart from its basis top and bottom, between to-rymi there is a strobiloid deepening (recessus pinealis). Between an upper surface of leads, a pinus and a vascular basis of the third ventricle nadshishkovidny deepening (recessus suprapinealis) is located. Both deepenings open in the third ventricle. As continuation of a plate of marrow serve leads. The right and left leads are connected among themselves by commissure of leads (commissura habenularum). In front they pass into the triangles of leads representing expansion of the back end of brain strips (striae medullares thalami) and containing medial and lateral kernels of leads in which fibers olfactory povodkovogo a bunch terminate. The lower brain plate, being dugoobrazno bent, goes to a roof of a mesencephalon. In the field of top of a bend there is an epitalamichesky (back) commissure.
The third ventricle (ventriculus tertius) is P.'s cavity of m, represents the narrow crack located in the sagittal plane (see. Ventricles of a brain ). Its sidewalls are formed by the medial surfaces of a thalamus and a hypothalamus. The front wall is made by a terminal plate, front commissure and columns of the arch. Between a column of the arch and a thalamus there is an interventricular foramen (foramen interventriculare) reporting the third ventricle with a side ventricle of the relevant party. The upper wall is formed by a vascular basis of the third ventricle. On the parties from the centerline in a vascular basis the vascular texture of the third ventricle is put. The back wall of the third ventricle is made by commissure of leads, the basis of a pinus and epitalamichesky (back) commissure. Is slightly lower than the last the opening of a water supply system of a brain (aqueductus cerebri) connecting the third and fourth ventricles is located. As the lower wall (bottom) of the third ventricle serve visual decussation, a gray hillock with a funnel, mamillary bodies, the back made a hole substance. In the field of the lower wall there are a visual deepening (recessus opticus) located kpered from visual decussation and deepening of a funnel (recessus infundibuli). The cavity of the third ventricle is covered by an ependyma (see).
In blood supply Items of m participate branches of front and back brain arteries, a front fleecy artery, front and back connecting, internal sleepy and basilar arteries. Outflow of blood from P. is carried out by m in internal brain, big brain and basal veins, and then in sine of a firm meninx.
Variety of functions P. of m speaks as properties of its educations: a thalamus, a hypothalamus, a metathalamus, an epithalamus, and bilateral ties of P. of m with structures of limbic system (see), a reticular formation of a mesencephalon (see. Reticular formation ) and a cerebral cortex (see). The thalamus is the subcrustal center of all types of sensitivity since all afferent conduction paths of c. N of page (see. Conduction paths ) before receipt in a cerebral cortex have a synoptic break in its specific kernels connected with certain areas of a cerebral cortex. Nonspecific kernels of a thalamus are connected with basal kernels (see) and various sites of a cerebral cortex, they provide maintenance of a certain level of excitability of a brain necessary for perception of irritations from the environment.
The main function of a hypothalamus is regulation of constancy of internal environment of an organism (see. Homeostasis ). It possesses the leading role in maintenance of a certain level of a metabolism, in regulation of temperature balance, functions of digestive, cardiovascular, secretory, respiratory and endocrine systems (see. Hypothalamic neurohormones , Gipotalamo-gipofizarnaya system , Neurohumoral regulation ). Hypothalamic educations of P. of m thanks to close ties with a hypophysis carry out power providing locomotion by adequate reorganization of exchange processes in an organism.
The metathalamus is the subcrustal center of hearing and sight. Functions of formations of an epithalamus are insufficiently studied. The pinus is a closed gland and melatonin (the antagonist of Intermedinum) exerting impact on contents in cells of melanin and some other physiologically active agents emits hormone. Assume that melatonin oppresses gonadotropic function of a hypophysis and function of gonads, participates in work of a so-called biological clock. Kernels of leads are connected with the olfactory analyzer (see).
With the help elektrofiziol. methods and anatomo-clinical observations the importance of educations of P. of m in regulation of functions of internals, in formation of various behavioural reactions is established. The item of m plays an essential role in regulation of movements (see), participating in association of separate elements of locomotion in the act of movement and in establishment of an order of separate phases of locomotion. The local irritation of sites P. of m, first of all a hypothalamus, electric current or chemical substances is followed by various behavioural reactions of animals: nastorazhivaniye, approximate and research reaction. Affective and defensive reactions are described (see. Emotions ), at which animals show readiness for protection, and at continuation or strengthening of irritation repeated attacks of rage are noted. In a thalamus and a hypothalamus various animals have zones of self-stimulation (see). It is established that P.'s educations in m are the subcrustal centers of the major biol. motivations (see) — food, drinking, sexual, etc. Various influences of educations of P. of m on activity of a cerebral cortex defining a condition of a dream and wakefulness are described.
Animals with completely removed with a cerebral cortex and basal kernels, but with the kept thalamus received the name of diencephalic or thalamic animals. At these animals such difficult motive acts as swallowing, chewing, a lakaniye, suction remain, there is normal a body temperature, the correct rhythm of respiratory movements, emotional reactions like imaginary rage, self-stimulation, etc. are characteristic of them. Diencephalic animals are capable to movement in space while at animals with P.'s section of m below a thalamus this function is broken. However unlike dogs, cats, rabbits and birds who after removal of a cerebral cortex at preservation of a thalamus can carry out the difficult coordinate movements at primacies characteristic tonic frustration are noted. So, diencephalic monkeys cannot go, their typical pose is observed: extremities of that party, on a cut the animal lies, are unbent, on the opposite side they are bent, and on an upper extremity the grasp reflex comes to light. Thus, than the organization of an animal is higher, especially serious violations are noted during removal of a cerebral cortex and basal kernels. It occurs owing to corticalization of functions in the course of phylogenesis, i.e. moving of difficult nervous functions to the highest and most late developing departments of c. N of page — a cerebral cortex.
A symptom complex of defeat of a diencephalon
Depending on localization patol. process allocate symptom complexes of damage of a thalamus, a hypothalamus, a metathalamus and an epithalamus.
The symptom complex of damage of a thalamus arises at tumors, vascular, infectious and dystrophic damages of a thalamus (see) also it is shown by a complex of motive, sensitive, mental and vegetative disorders which expressiveness depends on localization of defeat of basic groups of neurons of a thalamus. Tumors of a thalamus are followed by bystry increase in intracranial pressure owing to a prelum of likvorny ways (see. Hypertensive syndrome ). The most accurately expressed a wedge. syndromes of damage of a thalamus are noted at ischemic strokes (see) in the pool of the arteries supplying a thalamus with blood. The Posterolateralny thalamic syndrome — the classical thalamic syndrome described in 1906 by Zh. Dezherin and G. of Russia arises at strokes owing to defeat of the thalamic branch supplying with blood posterolateral department of a thalamus. It is characterized by quickly regressing contralateral hemiparesis, the steady contralateral hemianaesthesia which is followed in some cases by an astereognosis, paroxysmal unrestrained pains and the choreoathetoid movements in the affected extremities.
The Anterolateralny thalamic syndrome (a rubrotalamichesky syndrome) arises at strokes owing to defeat of the thalamic branch supplying an anterolateral part of a thalamus and is shown by the involuntary movements in contralateral extremities (a tremor of rest, an intentsionny tremor, the choreoathetoid movements) with development of the so-called thalamic arm described in 1925 Russia and Kornil. In some cases paresis of a look is noted.
The medial thalamic syndrome can be observed not only at vascular, but also at tumoral and dystrophic defeats of a medial part of a thalamus. At the same time the expressed vegetative and mental disturbances are noted (dysmnesias, hallucinations, disturbances in the affective sphere, dementia sometimes develops).
The symptom complex of defeat of a hypothalamus is characterized by neuroendocrinal, neurotrophic, visceral and trophic and mental disorders, disturbances of thermal control, a dream (see. Hypothalamic syndrome ).
The symptom complex of damage of a metathalamus usually is a part of a syndrome of more massive defeat of P. of m. At defeat of a kernel of a lateral cranked body the contralateral gomonimny hemianopsia (see), motor and pupillary frustration, disturbances of vision is noted (a thalamic blindness, metamorphopsias, monocular poppy-roisii). At defeat of a kernel of a medial cranked body there is a decrease in hearing, a perversion of sound perception (a hyperacusia, a paramuziya), etc.
The symptom complex of defeat of an epithalamus develops at tumors of an epithalamus (a pinealoma, a glioma) more often. At the same time the internal ophthalmoplegia - is observed (see), the paresis of a look up described in 1883 Mr. of H. Parinaud in connection with a compression of tserebellorubrotalamichesky ways can sometimes arise a bilateral cerebellar ataxy (see). At to a pinealoma (see) at children growth disorder of a skeleton and premature puberty are possible.
See also Brain .
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