Vagus nerve heart
Stimulation of the vagus nerves causes inhibition of contractions of the heart until it stops in diastole (the brothers Weber, 1845). In the history of the physiology of this fact was the first case of the retarding effect on the body to the stimulation of the nerve. Slow heartbeat during stimulation of the vagus nerves is referred to as a negative chronotropic action.
In addition, stimulation of the vagus nerve causes a decrease in excitability of the heart (bathmotropic negative action), lowering the rate of conduction of excitation in the heart (dromotropic negative action), decrease in strength of heart contractions (negative inotropic effect), increased muscle relaxation in diastole (tonotropnoe negative effect).
The right vagus nerve is predominantly negative chrono-and inotropic effect in atria and the left vagus nerve – mostly negative inotropic effect and Drome in the ventricles.
Dromotropic negative impact of the vagus nerves may say that the atria begin to contract more frequent pace than the ventricles, which indicates a partial block between the atria and ventricles.
With continued strong stimulation of the vagus nerve in warm-blooded animals there is “escape” of the heart from the influence of these nerves. Despite the fact that the nerve irritation continues, heart begins to approach normal. However, complete termination of braking does not occur. Thus, avoiding the deadly danger of cardiac arrest. This “escape” is supposed to be associated with the action of sympathetic nerves.
In contrast to the sympathetic nerve nucleus of the vagus nerves in the medulla oblongata are more clearly defined tone. The phenomenon of tone nuclei of the vagus nerves is that they are constantly in a state of excitation. It was found that the tone of the nuclei of the vagus nerves maintains a presence in the blood of adrenaline and calcium ions. These substances stimulate the sympathetic nervous system.
In the laboratory was shown that the excitation of sympathetic nerves facilitates the inhibitory effect of the vagus nerves.
Vagal tone increases with an increase in the intracranial pressure and the pressure in the blood vessels of the medulla oblongata, in the aorta, the carotid artery bifurcation and the other blood vessels, and when excited receptors located in other areas of the body.
In 1884 Vvedenskii proved that during deceleration caused by the vagus nerve, in the heart of the recovery taking place, assimilation (anabolic) processes.
Relations between wandering and sympathetic nerves of the heart. Between the two pairs of nerves there no relationship of antagonism and cooperation.
Transection of the nerves of the heart speeds up his work, indicating that the prevalence of tone centers on the vagus nerve sympathetic. Animals after this operation can not produce amplified motions, as there is no regulation of the heart.
Increasing and strengthening of the heart is obtained not only in the excitation of sympathetic nerves, but at the same time decreasing vagal tone. Conversely, slowing down and weakening of the heart occurs not only with an increase vagal tone, but while reducing a tone of the sympathetic nerves.
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