Heart nerves

The heart receives sensitive, sympathetic and parasympathetic innervation. Sympathetic fibers running from the right and left sympathetic trunks as part of the heart nerves carry impulses that accelerate the heart rate and expand the lumen of the coronary arteries, and parasympathetic fibers (a component of the cardiac branches of the vagus nerves) conduct impulses that slow down the heart rate and narrow the lumen of the coronary arteries ... Sensory fibers from the receptors of the walls of the heart and its vessels go as part of the heart nerves and cardiac branches to the corresponding centers of the spinal cord and brain.

The scheme of innervation of the heart (according to V.P. Vorobiev) can be represented as follows: sources of innervation of the heart are the heart nerves and branches that follow to the heart; extraorganic cardiac plexuses (superficial and deep), located near the aortic arch and pulmonary trunk; intraorgan cardiac plexus, which is located in the walls of the heart and is distributed in all their layers.

Cardiac nerves(upper, middle and lower cervical, as well. thoracic) begin from the cervical and upper thoracic (II-V) nodes of the right and left sympathetic trunks (see "The autonomic nervous system"). Cardiac branches originate from the right and left vagus nerves (see "Vagus nerve").

Superficial extraorgan cardiac plexuslies on the anterior surface of the pulmonary trunk and on the concave semicircle of the aortic arch; deep extraorgan cardiac plexuslocated behind the aortic arch (in front of the tracheal bifurcation). The upper left cervical heart nerve (from the left upper cervical sympathetic node) and the upper left cardiac branch (from the left vagus nerve) enter the superficial extraorgan cardiac plexus. All the other cardiac nerves and cardiac branches mentioned above enter into the deep extraorganic cardiac plexus.

The branches of the extraorganic cardiac plexuses pass into a single intraorgan cardiac plexus.Depending on which of the layers of the heart wall it is located in, this single intraorgan cardiac plexus is conditionally subdivided into closely related subepicardial, intramuscular and subendocardial plexus.The intraorganic cardiac plexus contains nerve cells andtheir clusters, forming small-sized nerve heart nodules, ganglia cardiaca. There are especially many nerve cells in the subepicardial plexus of the heart. According to V.P. Vorobyov, the nerves that are part of the subepicardial cardiac plexus have regular localization (in the form of nodal fields) and innervate certain parts of the heart. Accordingly, there are six subepicardial cardiac plexuses: 1) right frontand 2) left front.They are located in the thickness of the anterior and lateral walls of the right and left ventricles on both sides of the arterial cone; 3) anterior atrial plexus- in the anterior wall of the atria; 4) right posterior plexusdescends from the posterior wall of the right atrium to the posterior wall of the right ventricle (fibers from it go to the sinus-atrial node of the cardiac conduction system); five) left posterior plexusfrom the lateral wall of the left atrium continues down to the posterior wall of the left ventricle; 6) posterior plexus of the left atrium(Haller's sinus plexus) is located in the upper part of the posterior wall of the left atrium (between the orifices of the pulmonary veins).

The bodies of the first neurons are located in the medulla oblongata (Fig.).

Preganglionic nerve fibers are part of the vagus nerves and end in the intramural ganglia of the heart. Here are the second neurons, the processes of which go to the conducting system, the myocardium and coronary vessels. In the ganglia are H-cholinergic receptors (mediator - acetylcholine). M-cholinergic receptors are located on the effector cells. ACh, formed at the endings of the vagus nerve, is rapidly destroyed by the enzyme cholinesterase, which is present in the blood and cells, therefore ACh has only a local effect.

Data were obtained indicating that, upon excitation, along with the main mediator substance, other biologically active substances, in particular peptides, enter the synaptic cleft. The latter have a modulating effect, changing the magnitude and direction of the heart's reaction to the main mediator. Thus, opioid peptides inhibit the effects of irritation of the vagus nerve, while delta sleep peptide enhances vagal bradycardia.

Fibers from the right vagus nerve innervate mainly the sinoatrial node and, to a lesser extent, the myocardium of the right atrium, and the left one - the atrioventricular node.

Therefore, the right vagus nerve affects mainly the heart rate, and the left one affects AV conduction.

Parasympathetic innervation of the ventricles is weakly expressed and exerts its influence indirectly - inhibition of sympathetic effects.

The influence on the heart of the vagus nerves was first studied by the Weber brothers (1845). They found that irritation of these nerves slows down the work of the heart until it stops completely in diastole. This was the first case of the discovery of the inhibitory effect of nerves in the body.

The mediator of the neuromuscular synapse - acetylcholine - acts on M 2 -cholinoreceptors of cardiomyocytes.

Several mechanisms of this action are being studied:

Acetylcholine can activate the K + -channels of the sarcolemma through the G-protein, bypassing the second mediators, which explains its short latency period and short aftereffect. For a longer time, it activates K + channels through the G-protein, stimulating guanylate cyclase, increasing the formation of cGMP and the activity of protein kinase G. An increase in the release of K + from the cell leads to:

to an increase in membrane polarization, which reduces excitability;

slowing down the speed of DMD (slowing down the rhythm);

slowing down the conduction in the AV node (as a result of a decrease in the rate of depolarization);

shortening of the "plateau" phase (which reduces the Ca 2+ current entering the cell) and a decrease in the force of contraction (mainly of the atria);

at the same time, the shortening of the "plateau" phase in atrial cardiomyocytes leads to a decrease in the refractory period, i.e., increased excitability (there is a risk of atrial extra
systole, for example during sleep);

Acetylcholine exerts an inhibitory effect on adenylate cyclase through the Gj-protein, reducing the level of cAMP and the activity of protein kinase A. As a result,

With irritation of the peripheral segment of the cut vagus nerve or direct exposure to acetylcholine, negative batmo-, dromo-, chrono- and inotropic effects are observed.

Fig. ... Typical changes in action potentials of sinoatrial node cells upon stimulation of the vagus nerves or direct action of acetylcholine. Gray background - initial potential.

Typical changes in action potentials and myogram under the influence of the vagus nerves or their mediator (acetylcholine):

Escape of the heart from the influence of the vagus nerve

With prolonged irritation of the vagus nerve, the contractions of the heart that stopped at the beginning are restored, despite the continued irritation. This phenomenon is called the escape of the heart from the influence of the vagus nerve (Fig.).

INERVATION OF THE HEART

The heart is innervated by the autonomic nervous system, which regulates the generation of arousal and the conduction of impulses. It consists of sympathetic and parasympathetic nerves.

Preganglionic sympathetic fibers extend from the upper 5 thoracic segments of the spinal cord. They have synapses in the upper, middle and lower cervical ganglia and in the stellate ganglion. Postganglionic fibers that form sympathetic heart nerves depart from them. The branches of these nerves go to the sinus and atrioventicular nodes, the conductive tissue of the muscles of the atria and ventricles, and the coronary arteries. The effect of the sympathetic nerve is mediated by the mediator noradreanaline, which is formed at the endings of the sympathetic fibers in the myocardium. Sympathetic fibers increase the heart rate and are therefore called cardioaccelerator.

The heart receives parasympathetic fibers from the vagus nerve, the nuclei of which are located in the medulla oblongata. 1-2 branches extend from the cervical part of the trunk of the vagus nerve, and 3-4 branches from the chest part. The preganglionic fibers have their synapses in the intramural ganglia located in the heart. Postganglionic fibers go to the sinus and atrioventricular nodes, the atrial muscles, the upper part of the His bundle and the coronary arteries. The presence of parasympathetic fibers in the ventricular muscle has not yet been proven. The mediator of parasympathetic fibers is acetylcholine. The vagus nerve is a cardio-inhibitor: it slows down the heart rate by inhibiting the sinus and atrioventricular nodes.

Afferent nerve impulses from blood vessels, aortic arch and carotid sinus are conducted to the cardiovascular regulatory center in the medulla oblongata, and efferent nerve impulses from the same center through parasympathetic and sympathetic nerve fibers to the sinus node and the rest of the conduction system and coronary vessels.

HEART RATE REGULATION

The electrophysiological processes of the origin and conduction of excitation impulses into the conduction system and the myocardium are influenced by a number of regulatory neurohumoral factors. Despite the fact that the formation of impulses in the sinus node is an automatic process, it is under the regulatory influence of the central and autonomic nervous system. The sinus and atrioventricular nodes are exclusively influenced by the vagus nerve and, to a lesser extent, by the sympathetic. The ventricles are controlled only by the sympathetic nerve.

The effect of increased vagus tone on the heart rate (acetylcholine effect)

Inhibits the function of the sinus node and can cause sinus bradycardia, sinus blockade, failure of the sinus node ("sinus arrest")

Accelerates conduction in the atrial muscles and shortens its refractory period

Slows down conduction in the atrioventricular node and can cause varying degrees of atrioventricular block

Inhibits contractility of the myocardium of the atria and ventricles

Effect of increased sympathetic nerve tone on heart rate (norepinephrine effect)

Increases sinus node automatism and causes tachycardia

Accelerates conduction in the atrioventricular node and shortens the PQ interval

Increases the excitability of the atrioventricular node and may generate an active junctional rhythm

Shortens systole and increases the force of myocardial contraction

Increases the excitability of the atrial and ventricular myocardium and may cause flicker

The autonomic nervous system, in turn, is influenced by both the central nervous system and a number of humoral and reflex influences. It serves as a link between the cardiovascular system in general and the central nervous system, resp. the cerebral cortex, which is subject to the higher autonomic centers that lie in the hypothalamus. The role of the central nervous system and its influence on the frequency and rhythm of cardiac activity are well known and in this respect have been repeatedly studied in experimental and clinical conditions. Under the influence of the experienced strong joy or fright, or other positive or negative emotion, irritation of the vagus and (or) sympathetic nerve can be caused, which causes various kinds of rhythm and conduction disturbances, especially in the presence of myocardial ischemia or hyperactivity of neuromuscular reflexes. In some cases, such changes in heart rate are in the nature of a conditional connection. In clinical practice, there are many patients in whom extrasystoles appear only with the memory of a known experienced trouble.

Mechanisms that regulate the heart rhythm

In the medulla oblongata is the vagal nucleus, in which the parasympathetic center slowing down the heart is located. Proximal to it, in the reticular formation of the medulla oblongata, lies a sympathetic center accelerating cardiac activity. A third such center, also located in the reticular formation of the medulla oblongata, causes contractions of peripheral arterial vessels and increases blood pressure - the sympathetic vasoconstrictor center. All these three centers make up a single regulatory system and therefore they are united under the general name of the cardiovascular center.

The latter is under the regulatory influence of the subcortical nodes and the cerebral cortex (Fig. 13).

The rhythm of cardiac activity is also influenced by impulses emanating from the interoreceptive zones of the cardio-aortic, carotid sinus and other plexuses. Impulses emanating from these zones cause acceleration or deceleration of cardiac activity.

Innervation of the heart and nervous regulation of the heart rhythm.

Factors affecting the cardiovascular center in the medulla oblongata

Humoral changes in the blood and the chemoreceptor reflex. The center of regulation of cardiovascular activity is directly influenced by the partial pressure of CO 2, O 2 and blood pH, as well as an indirect effect - the chemoreceptor reflex from the aortic arch and carotid sinus.

Pressoreceptor reflex. In the arch of the aorta and the carotid sinus there are sensitive bodies - baroreceptors that respond to changes in blood pressure. They are also associated with regulatory centers in the medulla oblongata.

Bainbridge Reflex. The pulmonary veins, the superior and inferior vena cava and the right atrium contain baroreceptors associated with regulatory nuclei in the medulla oblongata.

Goering-Breuer reflex (the effect of breathing phases on the heart rate). Afferent fibers from the lung go along the vagus nerve to the centers of regulation of cardiac activity in the medulla oblongata. Inhalation causes oppression of the vagus nerve and acceleration of cardiac activity. Exhalation irritates the vagus nerve and slows down the heart. This reflex is especially well pronounced in sinus arrhythmias. After the application of atropine or physical activity, the vagus nerve is inhibited and the reflex does not appear.

Reflex Bezold-Jarisch. The receptor organ for this reflex is the heart itself. In the myocardium of the atria and ventricles, especially subendocardial, there are baroreceptors that are sensitive to changes in intraventricular pressure and tone of the heart muscle. These receptors are connected with the centers of regulation in the medulla oblongata with the help of afferent fibers of the vagus nerve.

It was found that the intercalated discs connecting the myocardial cells have a different structure. Some sections of the intercalated discs perform a purely mechanical function, others provide the transport of the substances necessary for it through the cardiomyocyte membrane, and others - nexuses, or close contacts, conduct excitation from cell to cell. Violation of intercellular interactions leads to asynchronous excitation of myocardial cells and the appearance of cardiac arrhythmias.

Intercellular interactions should also include the relationship of cardiomyocytes with connective tissue cells of the myocardium. The latter are not just a mechanical support structure. They supply the contractile cells of the myocardium with a number of complex high molecular weight products necessary to maintain the structure and function of the contractile cells. This type of intercellular interactions was called creative connections (G.I.Kositsky).

The effect of electrolytes on the activity of the heart.

Influence of K +

An increase in the level of extracellular K + increases the potassium permeability of the membrane, which can lead to both its depolarization and hyperpolarization. Moderate hyperkalemia (up to 6 mmol / l) more often causes depolarization and increases the excitability of the heart. High hyperkalemia (up to 13 mmol / l) more often causes hyperpolarization, which inhibits excitability, conduction and automation up to cardiac arrest in diastole.

Hypokalemia (less than 4 mmol / L) reduces membrane permeability and K + / Na + -Hacoca activity, therefore depolarization occurs, causing an increase in excitability and automation, activation of heterotopic foci of excitation (arrhythmia).

Influence of Ca 2+

Hypercalcemia accelerates diastolic depolarization and heart rate, increases excitability and contractility, a very high concentration can lead to cardiac arrest in systole.

Hypocalcemia reduces diastolic depolarization and rhythm.

Parasympathetic innervation of the heart

The bodies of the first neurons are located in the medulla oblongata (Fig.).

Preganglionic nerve fibers are part of the vagus nerves and end in the intramural ganglia of the heart. Here are the second neurons, the processes of which go to the conducting system, the myocardium and coronary vessels. In the ganglia are H-cholinergic receptors (mediator - acetylcholine). M-cholinergic receptors are located on the effector cells. ACh, formed at the endings of the vagus nerve, is rapidly destroyed by the enzyme cholinesterase, which is present in the blood and cells, therefore ACh has only a local effect.

Data were obtained indicating that, upon excitation, along with the main mediator substance, other biologically active substances, in particular peptides, enter the synaptic cleft. The latter have a modulating effect, changing the magnitude and direction of the heart's reaction to the main mediator. Thus, opioid peptides inhibit the effects of irritation of the vagus nerve, while delta sleep peptide enhances vagal bradycardia.

Fibers from the right vagus nerve innervate mainly the sinoatrial node and, to a lesser extent, the myocardium of the right atrium, and the left one - the atrioventricular node.

Therefore, the right vagus nerve affects mainly the heart rate, and the left one affects AV conduction.

Parasympathetic innervation of the ventricles is weakly expressed and exerts its influence indirectly - inhibition of sympathetic effects.

The influence on the heart of the vagus nerves was first studied by the Weber brothers (1845). They found that irritation of these nerves slows down the work of the heart until it stops completely in diastole. This was the first case of the discovery of the inhibitory effect of nerves in the body.

The mediator of the neuromuscular synapse - acetylcholine - acts on M 2 -cholinoreceptors of cardiomyocytes.

Several mechanisms of this action are being studied:

Acetylcholine can activate the K + -channels of the sarcolemma through the G-protein, bypassing the second mediators, which explains its short latency period and short aftereffect. For a longer period, it activates K + channels through the G-protein, stimulating guanylate cyclase, increasing the formation of cGMP and the activity of protein kinase G. An increase in the release of K + from the cell leads to:

to an increase in membrane polarization, which reduces excitability;

slowing down the speed of DMD (slowing down the rhythm);

slowing down the conduction in the AV node (as a result of a decrease in the rate of depolarization);

shortening of the "plateau" phase (which reduces the Ca 2+ current entering the cell) and a decrease in the force of contraction (mainly of the atria);

at the same time, a shortening of the "plateau" phase in atrial cardiomyocytes leads to a decrease in the refractory period, i.e., increased excitability (there is a risk of atrial extrasystoles, for example, during sleep);

Acetylcholine exerts an inhibitory effect on adenylate cyclase through the Gj-protein, reducing the level of cAMP and the activity of protein kinase A. As a result,

With irritation of the peripheral segment of the cut vagus nerve or direct exposure to acetylcholine, negative batmo-, dromo-, chrono- and inotropic effects are observed.

Fig. ... Typical changes in action potentials of sinoatrial node cells upon stimulation of the vagus nerves or direct action of acetylcholine. Gray background - initial potential.

Typical changes in action potentials and myogram under the influence of the vagus nerves or their mediator (acetylcholine):

The innervation of the heart is the supply of nerves that provide a connection between the organ and the central nervous system. While it sounds simple, it really isn't.

The main organ of the human circulatory system is the heart. It is hollow, reminiscent of a cone, located in the chest. If we describe its functions in simple words, then we can say that it works like a pump.

The peculiarity of the organ is that it can produce electrical activity on its own. This quality is defined called automation. Even a completely isolated heart muscle cell can contract on its own. In order for the body to work fully, this quality is necessary.

As mentioned above, the heart is located in the chest, the smaller part is localized on the right, and the larger on the left. So it is not worth thinking that the whole heart is located on the left, as this is wrong.

From childhood, children are told that the size of the heart is equal to the size of the hand, which is clenched into a fist, and this is actually the case. You should also be aware that the organ is divided into two halves, left and right. Each part has an atrium, a ventricle, and there is an opening between them.

Parasympathetic innervation

The heart receives not one, but several innervations at once - parasympathetic, sympathetic, sensitive. You should start with the first of all of the above.

Preganglionic nerve fibers can be classified as vagus nerves. They end in the intramural ganglia of the heart - these are nodes, which are a whole set of cells. The second neurons with processes are in the ganglia, they go to the conducting system, the myocardium and coronary vessels.

After excitation of the central nervous system, biologically active substances, as well as peptides, enter the synaptic cleft. This must be taken into account, since they have a modulating function.

Processes in progress

If we talk about the parasympathetic innervation of the heart further, then we cannot fail to note some important processes. You should know that the right vagus nerve affects heart rate, and the left one affects AV conduction. The innervation of the ventricles is poorly expressed, which is why the influence is indirect.

As a result of many complex processes, the following can occur:

1. Exit K + from the cell. The rhythm slows down, the refractory period decreases.
2. Protein kinase A activity is reduced. As a result, conductivity also decreases.

Attention should be paid to such a concept as the escape of the heart. This is a phenomenon in which the contraction stops due to the fact that the vagus nerve is excited for a long time. The phenomenon is considered unique, because this is how it is possible to avoid cardiac arrest.

Sympathetic innervation

It is almost impossible to describe the innervation of the heart briefly, all the more in language accessible to ordinary people. But dealing with the sympathetic is not so difficult, because the nerves are evenly distributed throughout the heart.

There are the first neurons called pseudo-unipolar cells. They are located on the lateral horns of the 5 upper segments of the thoracic spinal cord. The processes end in the cervical and upper nodes, the beginning of the second begins there, which in turn extend into the heart.

Sensitive innervation

It can be of two types - reflex and conscious.

Sensitive innervation of the first type is carried out as follows:

1. Nerve neurons of the spinal nodes... In the layers of the walls of the heart, receptor endings are formed by dendrites.
2. Second neurons... They are located in their own nuclei.
3. Third neurons... The site of localization is the ventrolateral nuclei.

Reflex innervation is provided by the neurons of the lower and upper nodes of the vagus nerves. Sensitive innervation is carried out with the help of Dogel's second type afferent cells.

Myocardium

The middle muscle layer of the heart is called the myocardium. This is the bulk of its mass. The main feature is contraction and relaxation. However, in general, the myocardium has four properties - conduction, contractility, excitability and automatism.

Each property should be considered in more detail:

1. Excitability... In simple terms, this is the heart's response to a stimulus. A muscle can only react to a strong stimulus; other forces will not be perceived. All this is because the myocardium has a special structure.
2. Conductivity and automatism... This is a unique feature of pacemaker cells to initiate spontaneous excitation. It appears in the conducting system, and then goes to the rest of the myocardium.
3. Contractility. This property is the easiest to understand, but there are some peculiarities here as well. Not many people know that the length of muscle fibers affects the strength of contraction. It is believed that the more blood flows to the heart, the more they stretch, respectively, the more powerful the contraction.

The health and condition of each person depends on the correctness of such a complexly arranged organ.

Muscle structure and blood flow

Above it was talked about what the parasympathetic, sympathetic and sensitive innervation of the heart is. The next point that is also important to consider is blood supply. It is not only difficult, but also interesting.

The human heart muscle is the very center of the blood supply process. Many people know at least approximately how the heart works. After the blood enters the organ, it passes into the atrium, then into the ventricle and large arteries. The biofluid movement is controlled by valves.

Interesting! Blood with low oxygen from the heart is sent to the lungs, where it is purified, and then saturated with oxygen.

After oxygenation, the blood flows into the venules, and then into the large veins. Through them, she goes back to the heart. In such a simple language, you can describe how the systemic circle of blood circulation works.

Heart volume

There is cardiac output and systolytic volume. Concepts are directly related to blood supply and innervation. The amount of blood ejected by the stomach over a certain amount of time is called the minute volume of the heart. In an adult and completely healthy person, this is about five liters.

Important! The volume for the left and right ventricles is equal.

If the minute volume is divided by the number of muscle contractions, then a new name will be obtained - the notorious systolytic. The calculation is actually extremely simple.

The heart of a healthy person contracts up to 75 times per minute. This means that the systolytic volume will be equal to 70 milliliters of blood. But it is worth noting that the indicators are generalized.

Prevention

Against the background of a complex topic about the innervation of the heart, a little attention should be paid to what actions can keep the organ functioning for long years.

Given the structural and operational features, it can be concluded that heart health depends on several main elements:

• blood flow;
• vessels;
• muscle tissue.

In order for the heart muscle to be in order, a moderate load must be placed on it. Walking or jogging will help you accomplish this mission. Simple exercises can temper the main organ of the body.

In order for the vessels to be normal, it is important to normalize your diet. You will have to say goodbye to portions of fatty foods forever. The body must receive the necessary micronutrients and vitamins, only then everything will be fine.

If we are talking about representatives of the age group, then in some cases the consistency can be so dangerous that it can provoke a stroke or heart attack. In order to somehow correct the situation, it is useful to walk in the evening, breathe fresh air.

Based on the foregoing, we can conclude that everything in the human body is interconnected, one cannot exist without the other. The longer the heart is healthy, the longer a person can live and enjoy life.

Frequently asked questions to the doctor

Heart health

What are the most effective ways to keep your heart healthy?

In order for your heart to please you with its work for many years and not let you down, you need to follow a few simple rules:

• proper nutrition;
• rejection of bad habits;
• preventive examinations;
• movement, even if there is no strength at all.

If throughout your life you follow simple recommendations, you will hardly complain about the work of the organ.