ENDOCARDIAC NERVOUS SYSTEM

From Big Medical Encyclopedia

ENDOCARDIAC NERVOUS SYSTEM — own nervous device of heart Including afferent, efferent and, perhaps, internuncial neurons. Shoots of neurons form in heart neuron - fabric and neuro neyronalnye synapses.

Morfol, researches B. of N of page were for the first time conducted by I. M. Dogel (1895), S. E. Mikhaylov (1907), V. P. Vorobyov (1917). V.'s studying N of page on special pilot models (on gomotransplantirovanny heart, in Krom all noncardiac nervous device is excluded and in the course of the experiment degenerated, and on heart with the broken innervatsionny relations), use by gistokhy. methods of a research (identification of mediators of an autonomous nervous system and the enzymes participating in their exchange) allowed to prove existence V.n.s with reliability. and to specify morfol, and some biochemical, features of the elements making it.

Afferent neurons of V. of N of page belong to ravnootrostchaty cells (a cell of the second type of Dogel). They possess the low-branching long dendrites which sensitive terminations are found on myocardial fibers, in connective tissue layers of a myocardium, in connecting fabric of an epicardium, endocardium, on arteries and veins of different caliber of all layers of a wall of heart. The axon of a ravnootrostchaty neurocyte forms one or two terminal branches creating synapses on efferent (dlinnoaksonny) or, perhaps on internuncial neurons. Efferent endocardiac neurons (dlinnoaksonny) of smaller size possess a large number of shoots. Their dendrites are short, repeatedly branch. Long axons in the terminal departments form the seteobrazny neuromuscular synoptic structures innervating a myocardium of auricles, ventricles, walls of coronary vessels. Among efferent (dlinnoaksonny) neurocytes thanks to use by gistokhy. methods of processing of drugs adrenergic and cholinergic nervous cells and, respectively, adrenergic and cholinergic neuromuscular synapses are found.

Emergence of rhythmic impulses of excitement in heart (the automaticity of heart) and their distribution to cells of a myocardium is function the carrying-out system of heart (see), the muscles of heart consisting of cardiomyocytes. Century of N of page regulates this function of the carrying-out system the same as function of a myocardium and a tone of coronary vessels, by means of intrakardialny peripheral reflexes. Besides, efferent neurons of V. of N of page provide transfer on working structures of heart of the impulses coming on preganglionic fibers of noncardiac nerves. As for fiziol, researches, already Goffmann's works (F. Century of Hoffmann, 1917), A. A. Zubkova (1935 — 1938), Bryukke (1936), Tiitso (M. of Tiitso, 1937), Schmidt (Page F. Schmidt, 1955), V. V. Zakusova (1958), etc. to a certain extent testified to a possibility of existence of endocardiac peripheral reflexes, however was considered to be that own nervous device of heart is only the place of switching of centrifugal impulses from preganglionic fibers of a vagus nerve on postganglionic.

The researches conducted by M. G. U delnovy with sotr. (1964 — 1975) and G. I. Kositsky with sotr. (1966 — 1975), for the first time showed that V. of N of page is capable to regulate functions of heart to a certain extent independently peripheral intrakardialny reflexes. Such type of regulation is one of links of difficult hierarchy of the nervous mechanisms regulating action of the heart. On efferent neurons of V. of N of page the impulses arising in V.'s receptors of N of page on intramural (endocardiac) peripheral reflex arcs and also the impulses coming to heart on preganglionic fibers of noncardiac nerves arrive. Thus, efferent neurons of V. of N of page are the general final way for impulses noncardiac and an intrakardialny origin.

In experiments on isolated hearts of frogs endocardiac nerves were exposed to artificial irritation. It was revealed that the electric irritation of the central end of one cut septal nerve caused emergence of bioelectric activity in other septal nerve. This effect remained after a degeneration of fibers of noncardiac nerves, but was switched off by ganglioblokator that demonstrated switching of impulses in V.'s gangliya of N of page. Researches showed that the intrakardialny nervous device takes part in regulation of a rhythm of cordial reductions, the speed of atrioventricular carrying out, in repolarization of muscular structures of a myocardium, and also in the speed of diastolic relaxation.

the Curves characterizing change of systolic pressure of blood in an aorta of a cat depending on its initial level (against the background of a zazhatiya of a pulmonary trunk): and — at a zazhatiya of a pulmonary trunk against the background of the low systolic pressure of blood in an aorta; — at a zazhatiya of a pulmonary trunk against the background of the high systolic pressure of blood in an aorta. I \pressure of blood in an aorta; II \a mark of time (one division — 1 sec.); III \mark zazhatiya of a pulmonary trunk.

G. I. Kositsky and sotr. peripheral intrakardialny reflexes at adequate irritation of receptors of V. of N of page are studied. Considering that afferent neurons of V. of N of page form typical stretch receptors (volyumoretseptor) on a myocardium, as an adequate irritant stretching of cameras of an isolated heart hematothermal was used by the inflowing blood or a barrel. At hemodynamic dissociation of the right and left half of heart it is revealed that stretching of a myocardium of one of cameras of heart causes strengthening of reduction not only the stretched department, but also a myocardium of other cameras which diastolic length of fibers did not change. Unlike the forward reactions of a myocardium which are carried out at its direct stretching according to the law of Starlinga (see. Starlinga law ), reactions of a myocardium of other cameras of heart were switched off at action of ganglioblokator and novocaine. The fact that observed reactions of a myocardium of an isolated heart arose at adequate irritation of mechanioreceptors and were switched off at action of neurotropic agents, and also were registered on hearts of the dogs isolated in several months after total noncardiac denervation demonstrates that these reactions arise on the mechanism of the endocardiac peripheral reflexes which are becoming isolated through endocardiac reflex hemlocks. The nature of inotropic reflex reactions was defined by initial degree of stretching of a myocardium and coronary vessels. So, with a pressure in an aorta it is lower than 80 mm of mercury. additional stretching of a myocardium of the right auricle or right ventricle caused positive inotropic reactions of a left ventricle; in a case when the irritation was carried out with a pressure in the mouth of an aorta higher than 100 mm of mercury., there was a weakening of reductions of a myocardium of a left ventricle (fig). Also it was established what V.n.s, regulates action of the heart according to conditions of the general hemodynamics and is capable to support the necessary level of blood circulation to a certain extent. So, in case of overflow of an aorta and coronary vessels blood the additional irritation of stretch receptors of a myocardium (e.g., at increase in inflow of blood to heart) causes oppression of force of cordial reductions. Thereof heart throws out in an aorta and a pulmonary trunk the smaller volume of blood, than at the reductions of ventricles preceding irritation. In cardial cavities there is a bigger amount of blood, and it in turn leads to increase of diastolic intracardiac pressure. Increase in end diastolic pressure reduces amount of the inflowing blood owing to what heart begins to pump over the smaller volume of blood in arterial system. It prevents overflow of arterial vessels, and the excess amount of blood is late in the veins having, as we know, considerable bigger capacity and ability considerably it to change.

In case of a short shot of heart blood (at small extent of excitement of stretch receptors of a myocardium) the additional irritation of these sensitive terminations arising normal at receipt of any portion of blood in cameras of heart causes reflex increase of force of cordial reductions. It promotes exile from cardial cavities of a large amount of blood in arterial system (due to reduction of the volume of blood which remained in cameras of heart by the time of a diastole). There is an increase in a pressure gradient between venas cava and heart that leads to strengthening of inflow and the best filling of heart during a diastole. Thereof heart begins to pump over blood in arterial system more intensively. Thus V. of N of page by intrakardialny peripheral reflexes is capable to regulate to a certain extent independently the mode of a hemodynamics in vessels of a big circle of blood circulation. Told allows to understand why total switching off of noncardiac nervous influences (e.g., at heart transplantations) significantly does not break regulation of general circulation. At various loads of an organism with gomotransplantirovanny heart the hemodynamics changes almost as well as normal, completely providing requirements of an organism.

Certificate of that V.'s activity and. the page is not completely autonomous, and represents one of links of difficult hierarchy of systems of nervous control of action of the heart, the fact that even with an invariable frequency of the impulses arriving on fibers of noncardiac nerves, changes of force of reductions will depend on the frequency of the impulses arising in afferent structures of heart and which are transferred to the same efferent intrakardialny neurons is. In this case with the same power of irritation of vagus nerves heart is capable to react variously depending on a condition of an endocardiac hemodynamics (e.g., positive inotropic reactions are observed in cases of a short shot of cameras of heart by blood).

Morfol, and gistokhy. data on existence in heart of two types of efferent neurons (cholinergic and adrenergic) allowed to assume that positive inotropic reactions of an isolated heart are implemented through adrenergic, and negative — through cholinergic neurons of V. and. page. Adrenergic intrakardialny neurons, apparently, have higher excitability, than cholinergic since irritation of receptors V.n.s, weak on force. causes a positive inotropic effect, and strong irritation of the same receptors — negative. The braking mechanism of adrenergic neurons with a high frequency of the arriving nervous impulses is finally not found out. It is possible that in cordial gangliya there can be nervous cells which carry out braking of adrenergic neurons owing to what the exciting effect cannot be implemented. According to the explanation offered by M. G. Udelnov, intensifying and brake reactions are carried out only with the participation of cholinergic neurons of a parasympathetic nervous system, and the nature of response depends at most irritations and respectively on number of the excited neurons. Pulse influences, various by quantity, cause in muscular structures of heart diverse electrotonic shifts which in turn cause multidirectional biochemical, changes that eventually leads to exciting or brake influence on heart.

Endocardiac peripheral reflexes can change excitability of a myocardium and participate in regulation of blood supply of a myocardium. The Intrakardialny nervous device to a certain extent can provide a certain interrelation between the level of sokratitelny ability and level of blood supply. These conclusions are based on data of change of a tone of coronary vessels at irritation of the sensitive terminations of own nervous system of heart in conditions when force and a rhythm of cordial reductions are practically left without changes.

The reflex changes of action of the heart which are carried out with participation of vagus nerves are result of interaction of the impulsation arising in receptors autonomic nervous system (see) and the impulses coming on preganglionic fibers of noncardiac nerves.

Pathology — see. Arrhythmias of heart , Ciliary arrhythmia , Bouveret's disease, Premature ventricular contraction .


Bibliography: V. P's sparrows. To topography of nervous trunks and nodes of heart of the person, Kharkiv, 1917; D about of e of l I. M. Comparative anatomy, physiology and pharmacology of heart, Kazan, 1895; To au-sitsky G. I. Afferent systems of heart, M., 1975; Kosits G. I. and Chervov's cue to I. A. Serdtsa as self-regulating system, M., 1968, bibliogr.; Krokhina E. M. Functional morphology and histochemistry of a vegetative innervation of heart, M., 1973; Udelnov M. G. Physiology of heart, M., 19 75, bibliogr.; E h i n g e r B. o. Adrenergic and cholinesterase — containing neurons of the heart, Histoche-mie, y. 16, p. 197, 1968, bibliogr.; J a-cobowitz D. Histochemical studies of the relationship of chromaffin cells and adrenergic nerve fibers to the cardiac ganglia of several species, J. Pharmacol, exp. Ther., v. 158, p. 227, 1967.

G. I. Kositsky, And. H. Dyakonova, I. A. Chervov.

Яндекс.Метрика