According to modern ideas respiratory center– this is a set of neurons that ensure a change in the processes of inhalation and exhalation and adaptation of the system to the needs of the body. There are several levels of regulation:

1) spinal;

2) bulbar;

3) suprapontial;

4) cortical.

Spinal level represented by motor neurons of the anterior horns of the spinal cord, the axons of which innervate the respiratory muscles. This component has no independent significance, since it is subject to impulses from the overlying departments.

Neurons of the reticular formation of the medulla oblongata and the pons form bulbar level. The following types of nerve cells are distinguished in the medulla oblongata:

1) early inspiratory (excited 0.1–0.2 s before the start of active inspiration);

2) full inspiratory (activated gradually and send impulses throughout the inhalation phase);

3) late inspiratory (begin to transmit excitation as the action of the early ones fades);

4) post-inspiratory (excited after inhibition of inspiratory);

5) expiratory (provide the beginning of active exhalation);

6) preinspiratory (begin to generate a nerve impulse before inhalation).

The axons of these nerve cells can be directed to motor neurons of the spinal cord (bulbar fibers) or be part of the dorsal and ventral nuclei (protobulbar fibers).

The neurons of the medulla oblongata, which are part of the respiratory center, have two features:

1) have reciprocal relationships;

2) can spontaneously generate nerve impulses.

The pneumotoxic center is formed by the nerve cells of the bridge. They are able to regulate the activity of underlying neurons and lead to a change in the processes of inhalation and exhalation. When the integrity of the central nervous system in the brainstem region is disrupted, the respiratory rate decreases and the duration of the inspiratory phase increases.

Suprapontial level represented by the structures of the cerebellum and midbrain, which provide regulation of motor activity and autonomic function.

Cortical component consists of neurons in the cerebral cortex that affect the frequency and depth of breathing. They generally have a positive effect, especially on the motor and orbital areas. In addition, the participation of the cerebral cortex suggests the possibility of spontaneously changing the frequency and depth of breathing.

Thus, various structures of the cerebral cortex play a leading role in the regulation of the respiratory process, but the bulbar region plays the leading role.

2. Humoral regulation of neurons of the respiratory center

Humoral regulation mechanisms were first described in the experiment of G. Frederick in 1860, and then studied by individual scientists, including I. P. Pavlov and I. M. Sechenov.

G. Frederick conducted a cross-circulation experiment in which he connected the carotid arteries and jugular veins of two dogs. As a result, the head of dog No. 1 received blood from the body of animal No. 2, and vice versa. When the trachea of ​​dog No. 1 was compressed, carbon dioxide accumulated, which entered the body of animal No. 2 and caused an increase in the frequency and depth of breathing in him - hyperpnea. Such blood entered the head of dog No. 1 and caused a decrease in the activity of the respiratory center until respiratory arrest (hypopnea and apopnea). Experience proves that the gas composition of the blood directly affects the intensity of breathing.

The excitatory effect on the neurons of the respiratory center is exerted by:

1) decreased oxygen concentration (hypoxemia);

2) increased carbon dioxide content (hypercapnia);

3) increased level of hydrogen protons (acidosis).

The braking effect occurs as a result of:

1) increased oxygen concentration (hyperoxemia);

2) decrease in carbon dioxide content (hypocapnia);

3) decreasing the level of hydrogen protons (alkalosis).

Currently, scientists have identified five ways in which the blood gas composition influences the activity of the respiratory center:

1) local;

2) humoral;

3) through peripheral chemoreceptors;

4) through central chemoreceptors;

5) through chemosensitive neurons of the cerebral cortex.

Local action occurs as a result of the accumulation of metabolic products in the blood, mainly hydrogen protons. This leads to activation of neurons.

Humoral influence appears with increased work of skeletal muscles and internal organs. As a result, carbon dioxide and hydrogen protons are released, which flow through the bloodstream to the neurons of the respiratory center and increase their activity.

Peripheral chemoreceptors– these are nerve endings from reflexogenic zones of the cardiovascular system (carotid sinuses, aortic arch, etc.). They react to lack of oxygen. In response, impulses begin to be sent to the central nervous system, leading to an increase in the activity of nerve cells (Bainbridge reflex).

The reticular formation includes central chemoreceptors, which have increased sensitivity to the accumulation of carbon dioxide and hydrogen protons. Excitation spreads to all zones of the reticular formation, including the neurons of the respiratory center.

Nerve cells of the cerebral cortex also respond to changes in blood gas composition.

Thus, the humoral link plays an important role in regulating the functioning of neurons of the respiratory center.

3. Nervous regulation of the activity of neurons in the respiratory center

Nervous regulation is carried out mainly by reflex pathways. There are two groups of influences – episodic and permanent.

There are three types of permanent ones:

1) from peripheral chemoreceptors of the cardiovascular system (Heymans reflex);

2) from proprioceptors of the respiratory muscles;

3) from the nerve endings of stretched lung tissue.

During the process of breathing, muscles contract and relax. Impulses from proprioceptors enter the central nervous system simultaneously to the motor centers and neurons of the respiratory center. Muscle function is regulated. If any breathing obstruction occurs, the inspiratory muscles begin to contract even more. As a result, a relationship is established between the work of skeletal muscles and the body's oxygen needs.

Reflex influences from lung stretch receptors were first discovered in 1868 by E. Hering and I. Breuer. They discovered that nerve endings located in smooth muscle cells provide three types of reflexes:

1) inspiratory-inhibitory;

2) expiratory-facilitating;

3) paradoxical Head effect.

During normal breathing, inspiratory inhibitory effects occur. During inhalation, the lungs stretch, and impulses from the receptors travel through the fibers of the vagus nerves to the respiratory center. Here, inhibition of inspiratory neurons occurs, which leads to the cessation of active inhalation and the onset of passive exhalation. The significance of this process is to ensure that exhalation begins. When the vagus nerves are overloaded, the change between inhalation and exhalation is maintained.

The expiratory facilitation reflex can only be detected during the experiment. If you stretch the lung tissue at the moment of exhalation, the onset of the next inhalation is delayed.

The paradoxical Head effect can be realized during an experiment. With maximum stretching of the lungs at the moment of inhalation, an additional inhalation or sigh is observed.

Episodic reflex influences include:

1) impulses from irrital receptors of the lungs;

2) influences from juxtaalveolar receptors;

3) influences from the mucous membrane of the respiratory tract;

4) influences from skin receptors.

Irritant receptors located in the endothelial and subendothelial layer of the respiratory tract. They simultaneously perform the functions of mechanoreceptors and chemoreceptors. Mechanoreceptors have a high threshold of stimulation and are excited when the lungs collapse significantly. Such drops normally occur 2–3 times per hour. When the volume of lung tissue decreases, receptors send impulses to the neurons of the respiratory center, which leads to additional inhalation. Chemoreceptors respond to the appearance of dust particles in mucus. When irritative receptors are activated, a sore throat and cough occur.

Juxtaalveolar receptors are located in the interstitium. They respond to the appearance of chemicals - serotonin, histamine, nicotine, as well as to changes in fluid. This leads to a special type of shortness of breath due to edema (pneumonia).

In case of severe irritation of the mucous membrane of the respiratory tract breathing stops, and in moderate cases protective reflexes appear. For example, when the receptors in the nasal cavity are irritated, sneezing occurs, and when the nerve endings of the lower respiratory tract are activated, a cough occurs.

The respiratory rate is influenced by impulses coming from temperature receptors. For example, when immersed in cold water, breathing occurs.

When noceceptors are activated First there is a cessation of breathing, and then there is a gradual increase in frequency.

During irritation of the nerve endings embedded in the tissues of the internal organs, a decrease in respiratory movements occurs.

As pressure increases, a sharp decrease in the frequency and depth of breathing is observed, which entails a decrease in the suction ability of the chest and restoration of blood pressure, and vice versa.

Thus, the reflex influences exerted on the respiratory center maintain the frequency and depth of breathing at a constant level.

It provides not only a rhythmic alternation of inhalation and exhalation, but is also capable of adjusting the depth and frequency of respiratory movements, thereby adapting pulmonary ventilation to the current needs of the body. Environmental factors, such as the composition and pressure of atmospheric air, ambient temperature and changes in the state of the body, for example, during muscular work, emotional arousal, and others, affecting the metabolic rate, and consequently, oxygen consumption and carbon dioxide release, act on the functional state of the respiratory center. As a result, the volume of pulmonary ventilation changes.

Like all other processes regulating physiological functions, regulation of breathing carried out in the body in accordance with the feedback principle. This means that the activity of the respiratory center, which regulates the supply of oxygen to the body and the removal of carbon dioxide formed in it, is determined by the state of the process it regulates. The accumulation of carbon dioxide in the blood, as well as the lack of oxygen, are factors that cause excitation of the respiratory center.

If the trachea of ​​one of these dogs is clamped and thus suffocating the body, then after a while it stops breathing (apnea), while the second dog experiences severe shortness of breath (dyspnea). This is explained by the fact that the compression of the trachea in the first dog causes an accumulation of CO2 in the blood of its body (hypercapnia) and a decrease in oxygen content (hypoxemia). Blood from the first dog's body enters the second dog's head and stimulates its respiratory center. As a result, increased breathing occurs - hyperventilation - in the second dog, which leads to a decrease in CO2 tension and an increase in O2 tension in the blood vessels of the body of the second dog. The oxygen-rich, carbon-dioxide-poor blood from this dog's body goes first to the head and causes apnea.

. Frederick's experience shows that the activity of the respiratory center changes with changes in the tension of CO2 and O2 in the blood. Particularly important for the regulation of the activity of the respiratory center is the change in carbon dioxide tension in the blood.

. Excitation of the inspiratory neurons of the respiratory center occurs not only when the carbon dioxide tension in the blood increases, but also when the oxygen tension decreases.

. The respiratory center receives afferent impulses not only from chemoreceptors, but also from pressoreceptors of the vascular reflexogenic zones, as well as from mechanoreceptors of the lungs, respiratory tract and respiratory muscles. All these impulses cause reflex changes in breathing. Of particular importance are the impulses coming to the respiratory center via the vagus nerves from the receptors of the lungs.

. There are complex reciprocal (conjugate) relationships between inspiratory and expiratory neurons. This means that excitation of inspiratory neurons inhibits expiratory ones, and excitation of expiratory neurons inhibits inspiratory ones. Such phenomena are partly due to the presence of direct connections that exist between the neurons of the respiratory center, but mainly they depend on reflex influences and on the functioning of the pneumotaxis center.

Like all other processes of automatic regulation of physiological functions, the regulation of breathing is carried out in the body based on the feedback principle. This means that the activity of the respiratory center, which regulates the supply of oxygen to the body and the removal of carbon dioxide formed in it, is determined by the state of the process it regulates. The accumulation of carbon dioxide in the blood, as well as the lack of oxygen, are factors that cause excitation of the respiratory center.

The importance of blood gas composition in the regulation of breathing was shown by Frederick through an experiment with cross-circulation. To do this, two dogs under anesthesia had their carotid arteries and separately jugular veins cut and cross-connected (Figure 2). After this connection and clamping of other neck vessels, the head of the first dog was supplied with blood not from its own body, but from the body of the second dog, the head of the second dog is from the body of the first.

If the trachea of ​​one of these dogs is clamped and thus suffocating the body, then after a while it stops breathing (apnea), while the second dog experiences severe shortness of breath (dyspnea). This is explained by the fact that compression of the trachea in the first dog causes an accumulation of CO 2 in the blood of its body (hypercapnia) and a decrease in oxygen content (hypoxemia). Blood from the first dog's body enters the second dog's head and stimulates its respiratory center. As a result, increased breathing occurs - hyperventilation - in the second dog, which leads to a decrease in CO 2 tension and an increase in O 2 tension in the blood vessels of the body of the second dog. The oxygen-rich, carbon-dioxide-poor blood from this dog's body goes first to the head and causes apnea.

Figure 2 - Scheme of Frederick's experiment with cross-circulation

Frederick's experience shows that the activity of the respiratory center changes with changes in the tension of CO 2 and O 2 in the blood. Let us consider the effect on breathing of each of these gases separately.

The importance of carbon dioxide tension in the blood in the regulation of respiration. An increase in carbon dioxide tension in the blood causes excitation of the respiratory center, leading to an increase in ventilation of the lungs, and a decrease in carbon dioxide tension in the blood inhibits the activity of the respiratory center, which leads to a decrease in ventilation of the lungs. The role of carbon dioxide in the regulation of breathing was proven by Holden in experiments in which a person was in a confined space of a small volume. As the oxygen content of the inhaled air decreases and the carbon dioxide content increases, dyspnea begins to develop. If you absorb the released carbon dioxide with soda lime, the oxygen content in the inhaled air can decrease to 12%, and there is no noticeable increase in pulmonary ventilation. Thus, the increase in the volume of ventilation of the lungs in this experiment is due to an increase in the content of carbon dioxide in the inhaled air.

In another series of experiments, Holden determined the volume of ventilation of the lungs and the content of carbon dioxide in the alveolar air when breathing a gas mixture with different contents of carbon dioxide. The results obtained are shown in Table 1.

breathing muscle gas blood

Table 1 - Volume of lung ventilation and carbon dioxide content in alveolar air

The data presented in Table 1 show that simultaneously with an increase in the content of carbon dioxide in the inhaled air, its content in the alveolar air, and therefore in the arterial blood, increases. At the same time, there is an increase in ventilation of the lungs.

The experimental results provided convincing evidence that the state of the respiratory center depends on the carbon dioxide content in the alveolar air. It was revealed that an increase in CO 2 content in the alveoli by 0.2% causes an increase in lung ventilation by 100%.

A decrease in the carbon dioxide content in the alveolar air (and, consequently, a decrease in its tension in the blood) reduces the activity of the respiratory center. This occurs, for example, as a result of artificial hyperventilation, i.e., increased deep and frequent breathing, which leads to a decrease in the partial pressure of CO 2 in the alveolar air and the tension of CO 2 in the blood. As a result, breathing stops. Using this method, i.e., by performing preliminary hyperventilation, you can significantly increase the time of voluntary breath holding. This is what divers do when they need to spend 2...3 minutes under water (the usual duration of voluntary breath-holding is 40...60 seconds).

The direct stimulating effect of carbon dioxide on the respiratory center has been proven through various experiments. Injection of 0.01 ml of a solution containing carbon dioxide or its salt into a certain area of ​​the medulla oblongata causes increased respiratory movements. Euler exposed isolated cat medulla oblongata to carbon dioxide and observed that this caused an increase in the frequency of electrical discharges (action potentials), indicating excitation of the respiratory center.

The respiratory center is influenced increasing the concentration of hydrogen ions. Winterstein in 1911 expressed the view that the excitation of the respiratory center is caused not by carbonic acid itself, but by an increase in the concentration of hydrogen ions due to an increase in its content in the cells of the respiratory center. This opinion is based on the fact that increased respiratory movements are observed when not only carbonic acid, but also other acids, such as lactic acid, are introduced into the arteries supplying the brain. Hyperventilation, which occurs with an increase in the concentration of hydrogen ions in the blood and tissues, promotes the release of part of the carbon dioxide contained in the blood from the body and thereby leads to a decrease in the concentration of hydrogen ions. According to these experiments, the respiratory center is a regulator of the constancy of not only the carbon dioxide tension in the blood, but also the concentration of hydrogen ions.

The facts established by Winterstein were confirmed in experimental studies. At the same time, a number of physiologists insisted that carbonic acid is a specific irritant of the respiratory center and has a stronger stimulating effect on it than other acids. The reason for this turned out to be that carbon dioxide penetrates more easily than the H+ ion through the blood-brain barrier, which separates the blood from the cerebrospinal fluid, which is the immediate environment that bathes the nerve cells, and more easily passes through the membrane of the nerve cells themselves. When CO 2 enters the cell, H 2 CO 3 is formed, which dissociates with the release of H+ ions. The latter are the causative agents of the cells of the respiratory center.

Another reason for the stronger effect of H 2 CO 3 compared to other acids is, according to a number of researchers, that it specifically affects certain biochemical processes in the cell.

The stimulating effect of carbon dioxide on the respiratory center is the basis of one measure that has found application in clinical practice. When the function of the respiratory center is weakened and the resulting insufficient supply of oxygen to the body, the patient is forced to breathe through a mask with a mixture of oxygen and 6% carbon dioxide. This gas mixture is called carbogen.

Mechanism of action of increased CO voltage 2 and increased concentration of H+ ions in the blood during respiration. For a long time it was believed that an increase in carbon dioxide tension and an increase in the concentration of H+ ions in the blood and cerebrospinal fluid (CSF) directly affect the inspiratory neurons of the respiratory center. It has now been established that changes in CO 2 voltage and the concentration of H + ions affect respiration, exciting chemoreceptors located near the respiratory center that are sensitive to the above changes. These chemoreceptors are located in bodies with a diameter of about 2 mm, located symmetrically on both sides of the medulla oblongata on its ventrolateral surface near the exit site of the hypoglossal nerve.

The importance of chemoreceptors in the medulla oblongata can be seen from the following facts. When these chemoreceptors are exposed to carbon dioxide or solutions with an increased concentration of H+ ions, stimulation of respiration is observed. Cooling of one of the chemoreceptor bodies of the medulla oblongata entails, according to Leschke’s experiments, the cessation of respiratory movements on the opposite side of the body. If the chemoreceptor bodies are destroyed or poisoned by novocaine, breathing stops.

Along with With chemoreceptors of the medulla oblongata in the regulation of breathing, an important role belongs to chemoreceptors located in the carotid and aortic bodies. This was proven by Heymans in methodologically complex experiments in which the vessels of two animals were connected so that the carotid sinus and carotid body or aortic arch and aortic body of one animal were supplied with the blood of another animal. It turned out that an increase in the concentration of H + ions in the blood and an increase in CO 2 voltage cause excitation of carotid and aortic chemoreceptors and a reflex increase in respiratory movements.

For the normal course of tissue metabolism, the O content is especially important 2 and CO 2 in arterial blood.

Regulation of external respiration

Ventilation of the lungs is the process of updating the gas composition of alveolar air, which ensures the supply of oxygen and the removal of carbon dioxide. This process is carried out by the rhythmic work of the respiratory muscles, changing the volume of the chest. The intensity of ventilation is determined by the depth of inspiration and breathing frequency. Thus, the minute volume of respiration is an indicator of pulmonary ventilation, which should ensure the gas homeostasis that is necessary in a specific situation (rest, physical work). Regulation of external respiration is the process of changing the minute volume of respiration in various conditions to ensure the optimal gas composition of the internal body environment.

In the second half of the 19th century, a hypothesis appeared that the main factors in the regulation of respiration are the partial pressure of oxygen and carbon dioxide in the alveolar air and, consequently, in the arterial blood. Experimental evidence that enrichment of arterial blood with carbon dioxide and depletion of oxygen enhances ventilation of the lungs as a result of the resulting excitation of the respiratory center was obtained in Frederick's classic experiment with cross-circulation in 1890 (Figure 13). In two anesthetized dogs, the carotid arteries and separately the jugular veins were cut and connected. After such connection and ligation of the vertebral arteries, the head of the first dog was supplied with blood from the second and vice versa. If the trachea was blocked in the first dog and asphyxia was caused in this way, then the second dog developed hyperpnea- increased pulmonary ventilation. In the first dog, despite the increase in carbon dioxide tension in the blood and the decrease in oxygen tension, after some time there occurred apnea- cessation of breathing movements. This is explained by the fact that the carotid artery of the first dog receives blood from the second dog, in which, as a result of hyperventilation, the carbon dioxide content in the arterial blood decreases. Even then it was established that the regulation of breathing occurs through feedback: deviations in the gas composition of arterial blood lead, by influencing the respiratory center, to such changes in breathing that reduce these deviations.

Figure 13. Schematic of Frederick's cross-circulation experiment.

Tracheal compression in Dog A causes shortness of breath in Dog B. Shortness of breath in Dog B causes breathing to slow and stop in Dog A

At the beginning of the 19th century, it was shown that in the medulla oblongata at the bottom of the fourth ventricle there are structures, the destruction of which by a needle prick leads to the cessation of breathing and the death of the body. This small area of ​​the brain in the lower corner of the rhomboid fossa was called the respiratory center.

Numerous studies have established that changes in the gas composition of the internal environment affect the respiratory center not directly, but by influencing special chemosensitive receptors located in the medulla oblongata - central (medullary) chemoreceptors and in vascular reflexogenic zones - peripheral (arterial) chemoreceptors.

During evolutionary development, the main function in stimulating the respiratory center moved from peripheral chemoreceptors to central ones. We are talking primarily about bulbar chemosensitive structures that respond to changes in the concentration of hydrogen ions and CO tension 2 in the extracellular fluid of the brain. Behind peripheral, arterial chemoreceptors, which are also excited when CO tension increases 2 , and with a decrease in oxygen tension in the blood washing them, only an auxiliary role in stimulating breathing remained.

Therefore, let us first consider the central chemoreceptors, which have a more pronounced effect on the activity of the respiratory center.

Have you heard about such an experiment on wine experts? I was once in France, where we tried 10-15 varieties of cognac costing from 100 to 10,000 dollars per bottle - I couldn’t distinguish anything there at all. Firstly, I’m not a specialist at all and don’t have any rich drinking experience, and secondly, cognac is still a strong thing.

But what they write about experiments with wine seems to me to be very exaggerated, simplistic, or their experts are so worthless. See for yourself.

Once upon a time, a wine tasting was held in Boston, in which famous connoisseurs of this drink took part. The rules for wine tasting were very simple. Twenty-five of the best wines, the price of which should not exceed $12, were purchased in a regular store in Boston. Later, a group of experts was formed to evaluate red and white wines, who were supposed to blindly identify the best wine from the presented...

As a result, the winner was the cheapest wine. This once again confirms that tasters and wine critics are a myth. Based on the results of the analysis of the experts' responses, it was revealed that all tasters chose the wine that they simply liked the most in taste. So much for the "experts".

By the way, in 2001, Frederic Brochet from the University of Bordeaux conducted two separate and very revealing experiments on tasters. In the first test, Brochet invited 57 experts and asked them to describe their impressions of just two wines.

In front of the experts were two glasses, with white and red wine. The trick was that there was no red wine, in fact it was the same white wine, tinted with food coloring. But that didn't stop experts from describing "red" wine in the language they usually use to describe red wines.

One expert praised its "jamminess" and another even "felt" the "crushed red fruit." No one noticed that it was actually white wine!!!

Brochet's second experiment turned out to be even more damning for critics. He took regular Bordeaux and bottled it in two different bottles with different labels. One bottle was grand cru, the other was regular table wine.

Even though they actually drank the same wine, the experts rated them differently. The Grand Cru was "pleasant, woody, complex, balanced and enveloping" and the table was, according to experts, "weak, tasteless, unsaturated, simple."

At the same time, most of them did not even recommend “table” wine for consumption.
Experts are fashion indicators and their taste is no different from the sense of taste of an ordinary person. People just want to listen to someone’s opinion, that’s what an “expert” is for.

The question arises: Do “experts” exist? In other words, we are different people, and our tastes vary just like brands of cheap wine, some like them, some don't.

Or, if not the brand and year of harvest, then white and red wine can be accurately distinguished even by a weak expert? How do you feel about wine experts?