VASOMOTOR CENTER — the morfofunktsionalny formation of a myelencephalon playing the leading role in maintenance of a tone of vessels and reflex regulation of blood pressure.
Page of c. it was opened by F. V. Ovsyannikov in 1871. He established also that S. of c. represents pair education since the section of a myelencephalon in the sagittal direction did not influence the ABP level.
By method of local stimulation in S. of c. existence of pressor and depressor zones is established (see. Depressory reactions , Pressor reactions ). The zone of pressor influences is localized in the field of the lower pole, at a top of a gray wing, and depressor — in the tail of a rhomboid pole. The obtained data on localization of pressor and depressor zones C. of c. caused emergence of the hypothesis stated by Beyliss (W. M of Bayliss, 1923), about existence of two vasculomotor centers of a nervous system — pressor (vasoconstrictive) and depressor (vasodilating) — with independent effector nerves (vasopressor and vazodilatatorny).
In reactions of all organism of S. of c. acts as executive body, through to-ry suprabul-bar influences considerably are implemented on hemodynamics (see). Influences of the most vasomotor center are carried out through a spinal cord, peripheral neurovegetative educations, vagus nerves and cause preferential system changes of a hemodynamics.
By further researches it was shown that, changing the frequency and intensity of electric current, it is possible to cause from the same point of S. of c. reactions of change of the ABP, opposite on an orientation. It is established also that both in rostrokaudalny, and in dorsoventral the directions pressor and depressor points are located diffuzno, mutually blocking each other. Thus, division into pressor and depressor zones is quite approximate since it is impossible to define precisely borders of zones because of their mutual overlapping. By means of microelectrode technics (see. Microelectrode method of a research ) it was shown that in the same zone both vasopressor and vazodilatator-ny neurons can be registered. It indicates a certain specificity of nek-ry neurons of S. of c. Functional distinction of neurons will be coordinated with idea of existence of pressor and depressor zones in S. of c. myelencephalon. The pressor area has «internal» tonic activity, edges thanks to peripheral sympathetic neurons are provided by tonic contraction of vessels. The depressor area renders reflex oppression of pressor department and activates parasympathetic vasodilating mechanisms. It is shown also that the depressor zone is the place of switching of the impulses arriving here from baroreceptors (see. Angiotseptora ) reflexogenic zones, to-rye lead to the central braking of tonic categories of the vasoconstrictors generated by pressor department of S. of c. At the same time relationship of pressor and depressor structures of a vasomotor center has difficult sinergoantagonistichesky character.
Page of c. has structural and diverse functional linkages with suprabulbarny, pontobulbarny and spinal regulatory formations of a brain. In reactions of a complete organism of S. of c. acts in close interaction with hypothalamus (see), cerebellum (see), basal kernels (see), cerebral cortex (see). If regulation of the main elementary functions blood pressure (see) S. is carried out by c directly. a myelencephalon, the highest form of regulation of blood circulation connected with power providing and integration of various and difficult adaptive acts and behavioural reactions is provided with more high levels of a brain.
S.'s tone of c. and, therefore, the level of the general ABP (see. Blood circulation ) are regulated by the impulses arising in vascular reflexogenic zones (see), hl. obr. in aortal and sinocarotid zones, the mouth of venas cava and vessels of a small circle of blood circulation, and also in hemoretseptorny zones (see. Chemoceptors ), of to-rykh the place of a branching of the general carotid arteries is main. Besides, S. of c. is a part reticular formation (see) a myelencephalon and therefore receives numerous collateral excitement from all specific conduction paths that supports him in a condition of tonic excitement.
For studying of the complex morfofunktsionalny organization C. of c. use methods of consecutive sections of a brainstem, local electric irritation and destruction of certain sites of c. N of page; a new step in S.'s studying c. use of methods of evoked potentials was (see. Bioelectric potential ) and microelectrode technics.
By many researchers it is shown that S. of c. is that point, in Krom fight of pressor and depressor influences is played. The convergent neurons changing spontaneous activity at pressor and depressor influences are considered as nodal cells, on to-rykh interaction of pressor hypothalamic and depressor barorecrptor influences is carried out. These neurons determine by the activity the result of antagonistic pressor and depressor relationship in self-control of the ABP. In case of long, steady suprabulbarny influences on vasoconstrictive department of S. of c. the depressor impulses coming to it are inefficient to cause falling of the ABP. It is a moment of rupture of developing of neurogenic hypertensia, as a result a cut the new patterns of generation of categories in barorecrptor devices which are expressed in their beginning adaptation form. Most of researchers consider that in any cases of development of steady arterial hypertension by the initiative moment disturbance of the intra central interactions in S. of c is. Opinions disperse only on a question where primary center of permanent excitement is localized (a hypothalamus, limbic system, bark). It is necessary to consider conventional that in any cases neurogenic hypertensia is connected with permanent increase in excitability of bulbar vasoconstrictive structures.
The morbid conditions connected with dysfunctions of a vasomotor center — see. arterial hypertension , Hypotension arterial , Dystonia vascular , Collapse , Neurocirculatory dystonia , Syncope , Vascular insufficiency .
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S. I. Kashtanov.