It refers to the protective respiratory reflexes of the body. Breathing reflexes

The regulation of respiration is carried out by reflex reactions resulting from the excitation of specific receptors in the lung tissue, vascular reflexogenic zones and other areas. The central apparatus for regulating respiration is represented by the formations of the spinal cord, medulla oblongata and overlying parts of the nervous system. The main function of breathing control is carried out by the respiratory neurons of the brain stem, which transmit rhythmic signals to the spinal cord to the motor neurons of the respiratory muscles.

Respiratory nerve center This is a collection of neurons of the central nervous system that ensure the coordinated rhythmic activity of the respiratory muscles and the constant adaptation of external respiration to changing conditions inside the body and in the environment. The main (working) part of the respiratory nerve center is located in the medulla oblongata. It has two departments: inspiratory(centre of inhalation) and expiratory(expiratory center). The dorsal group of respiratory neurons in the medulla oblongata consists mainly of inspiratory neurons. They partially give the flow of descending pathways that come into contact with motor neurons of the phrenic nerve. The ventral group of respiratory neurons sends predominantly descending fibers to the motoneurons of the intercostal muscles. In front of the pons Varolii, an area called pneumotaxic center. This center is related to the work of both experiential and inspiratory departments. An important part of the respiratory nerve center is a group of neurons in the cervical spinal cord (III-IV cervical segments), where the nuclei of the phrenic nerves are located.

By the time the child is born, the respiratory center is able to give a rhythmic change in the phases of the respiratory cycle, but this reaction is very imperfect. The point is that by birth the respiratory center is not yet formed, its formation ends by 5-6 years of age. This is confirmed by the fact that it is by this period in the life of children that their breathing becomes rhythmic and uniform. In newborns, it is unstable both in frequency and in depth and rhythm. Their breathing is diaphragmatic and practically differs little during sleep and wakefulness (frequency from 30 to 100 per minute). In children of 1 year, the number of respiratory movements during the day is within 50-60, and at night - 35-40 per minute, unstable and diaphragmatic. At the age of 2-4 years - the frequency becomes in the range of 25-35 and is predominantly of the diaphragmatic type. In 4-6 year old children, the respiratory rate is 20-25, mixed - thoracic and diaphragmatic. By the age of 7-14, it reaches the level of 19-20 per minute, it is at this time mixed. Thus, the final formation of the nerve center practically belongs to this age period.

How is the respiratory center stimulated? One of the most important ways of its excitation is automation. There is no single point of view on the nature of automation, but there is evidence that secondary depolarization may occur in the nerve cells of the respiratory center (according to the principle of diastolic depolarization in the heart muscle), which, reaching a critical level, gives a new impulse. However, one of the main ways of excitation of the respiratory nerve center is its irritation with carbon dioxide. In the last lecture, we noted that a lot of carbon dioxide remains in the blood flowing from the lungs. It performs the function of the main irritant of the nerve cells of the medulla oblongata. This is mediated through special education - chemoreceptors located directly in the structures of the medulla oblongata ( "central chemoreceptors"). They are very sensitive to the tension of carbon dioxide and the acid-base state of the intercellular cerebral fluid surrounding them.

Carbonic acid can easily diffuse from the blood vessels of the brain into the cerebrospinal fluid and stimulate the chemoreceptors in the medulla oblongata. This is another way of excitation of the respiratory center.

Finally, its excitation can also be carried out reflexively. We conditionally divide all reflexes that ensure the regulation of breathing into: own and conjugated.

Own reflexes of the respiratory system - these are reflexes that originate in the organs of the respiratory system and end in it. First of all, this group of reflexes should include the reflex act from lung mechanoreceptors. Depending on the localization and type of perceived stimuli, the nature of the reflex responses to irritation, three types of such receptors are distinguished: stretch receptors, irritant receptors, and juxtacapillary receptors of the lungs.

Stretch receptors in the lungs are located mainly in the smooth muscles of the airways (trachea, bronchi). There are about 1000 such receptors in each lung and they are connected with the respiratory center by large myelinated afferent fibers of the vagus nerve with a high speed of conduction. The direct stimulus of this type of mechanoreceptors is the internal tension in the tissues of the walls of the airways. When the lungs are stretched during inspiration, the frequency of these impulses increases. Inflating the lungs causes reflex inhibition of inhalation and transition to exhalation. When the vagus nerves are cut, these reactions stop, and breathing becomes slow and deep. These reactions are called reflex Goering Breuer. This reflex is reproduced in an adult when the tidal volume exceeds 1 liter (during exercise, for example). It is of great importance in newborns.

Irritant receptors or rapidly adapting airway mechanoreceptors, tracheal and bronchial mucosal receptors. They respond to sudden changes in the volume of the lungs, as well as to the action of mechanical or chemical irritants (dust particles, mucus, fumes of caustic substances, tobacco smoke, etc.) on the mucosa of the trachea and bronchi. Unlike pulmonary stretch receptors, irritant receptors are rapidly adaptable. When the smallest foreign bodies (dust, smoke particles) enter the respiratory tract, the activation of irritant receptors causes a cough reflex in a person. Its reflex arc is as follows - from the receptors, information through the upper laryngeal, glossopharyngeal, trigeminal nerve goes to the corresponding brain structures responsible for exhalation (urgent expiration - cough). If the receptors of the nasal airways are excited in isolation, then this causes another urgent expiration - sneezing.

Juxtacapillary receptors - located near the capillaries of the alveoli and respiratory bronchi. The irritant of these receptors is an increase in pressure in the pulmonary circulation, as well as an increase in the volume of interstitial fluid in the lungs. This is observed with stagnation of blood in the pulmonary circulation, pulmonary edema, damage to the lung tissue (for example, with pneumonia). Impulses from these receptors are sent to the respiratory center along the vagus nerve, causing frequent shallow breathing. In diseases, it causes a feeling of shortness of breath, shortness of breath. There may be not only rapid breathing (tachypneous), but also reflex constriction of the bronchi.

They also distinguish a large group of their own reflexes, which originate from the proprioceptors of the respiratory muscles. Reflex off proprioceptors of the intercostal muscles is carried out during inhalation, when these muscles, contracting, send information through the intercostal nerves to the expiratory section of the respiratory center, and as a result, exhalation occurs. Reflex off diaphragm proprioceptors is carried out in response to its contraction during inhalation, as a result, information enters through the phrenic nerves, first into the spinal cord, and then into the medulla oblongata to the expiratory section of the respiratory center, and exhalation occurs.

Thus, all own reflexes of the respiratory system are carried out during inhalation and end with exhalation.

Conjugate reflexes of the respiratory system - these are reflexes that start outside of it. This group of reflexes, first of all, includes a reflex to the conjugation of the activity of the circulatory and respiratory systems. Such a reflex act starts from the peripheral chemoreceptors of the vascular reflexogenic zones. The most sensitive of them are located in the area of the carotid sinus zone. Carotid sinus chemoreceptive conjugated reflex - occurs when carbon dioxide accumulates in the blood. If its tension increases, then the most highly excitable chemoreceptors are excited (and they are located in this zone in the carotid sinus body), the resulting wave of excitation goes from them along the IX pair of cranial nerves and reaches the expiratory section of the respiratory center. There is an exhalation, which enhances the release of excess carbon dioxide into the surrounding space. Thus, the circulatory system (by the way, during the implementation of this reflex act also works more intensively, the heart rate and blood flow rate increase) affects the activity of the respiratory system.

Another type of conjugated reflexes of the respiratory system is a large group exteroceptive reflexes. They originate from tactile (remember the reaction of breathing to touch, touch), temperature (heat - increases, cold - reduces respiratory function), pain (weak and medium strength stimuli - increase, strong - depress breathing) receptors.

Proprioceptive coupled reflexes respiratory system are carried out due to irritation of the receptors of skeletal muscles, joints, ligaments. This is observed during physical activity. Why is this happening? If at rest a person needs 200-300 ml of oxygen per minute, then during physical exertion this volume should increase significantly. Under these conditions, MO, the arteriovenous oxygen difference, also increases. An increase in these indicators is accompanied by an increase in oxygen consumption. Further, it all depends on the amount of work. If the work lasts 2-3 minutes and its power is large enough, then the oxygen consumption increases continuously from the very beginning of work and decreases only after it is stopped. If the duration of work is longer, then oxygen consumption, increasing in the first minutes, is subsequently maintained at a constant level. Oxygen consumption increases the more the harder the physical work. The largest amount of oxygen that the body can absorb in 1 minute with extremely hard work for it is called maximum oxygen consumption (MOC). Work in which a person reaches his level of IPC should last no more than 3 minutes. There are many ways to determine the IPC. In people who are not involved in sports or physical exercises, the value of the IPC does not exceed 2.0-2.5 l / min. In athletes, it can be more than twice as high. IPC is an indicator aerobic performance of the body. This is the ability of a person to perform very hard physical work, providing their energy costs due to oxygen absorbed directly during work. It is known that even a well-trained person can work with oxygen consumption at the level of 90-95% of his MIC level for no more than 10-15 minutes. The one who has a high aerobic capacity achieves the best results in work (sports) with relatively the same technical and tactical readiness.

Why does physical work increase oxygen consumption? There are several reasons for this reaction: the opening of additional capillaries and an increase in blood in them, a shift in the hemoglobin dissociation curve to the right and down, and an increase in temperature in the muscles. In order for the muscles to perform certain work, they need energy, the reserves of which are restored in them when oxygen is delivered. Thus, there is a relationship between the power of work and the amount of oxygen that is required for work. The amount of blood required for work is called oxygen demand. Oxygen demand can reach during hard work up to 15-20 liters per minute or more. However, the maximum oxygen consumption is two to three times less. Is it possible to perform work if the minute oxygen supply exceeds the MIC? To correctly answer this question, we must remember why oxygen is used during muscle work. It is necessary for the restoration of energy-rich chemicals that provide muscle contraction. Oxygen usually interacts with glucose, and it, being oxidized, releases energy. But glucose can be broken down without oxygen, i.e. anaerobically, while also releasing energy. In addition to glucose, there are other substances that can be broken down without oxygen. Consequently, the work of the muscles can be ensured even with an insufficient supply of oxygen to the body. However, in this case, many acidic products are formed and oxygen is needed to eliminate them, because they are destroyed by oxidation. The amount of oxygen required to oxidize metabolic products formed during physical work is called oxygen debt. It occurs during work and is eliminated in the recovery period after it. It takes from a few minutes to an hour and a half to eliminate it. It all depends on the duration and intensity of the work. The main role in the formation of oxygen debt is lactic acid. To continue working in the presence of a large amount of it in the blood, the body must have powerful buffer systems and its tissues must be adapted to work with a lack of oxygen. This adaptation of tissues is one of the factors providing high anaerobic performance.

All this complicates the regulation of breathing during physical work, since oxygen consumption in the body increases and its lack in the blood leads to irritation of chemoreceptors. Signals from them go to the respiratory center, as a result, breathing quickens. During muscular work, a lot of carbon dioxide is formed, which enters the blood, and it can act on the respiratory center directly through the central chemoreceptors. If the lack of oxygen in the blood leads mainly to increased respiration, then an excess of carbon dioxide causes its deepening. During physical work, both of these factors act at the same time, as a result of which both quickening and deepening of breathing occur. Finally, the impulses coming from the working muscles reach the respiratory center and intensify its work.

During the functioning of the respiratory center, all its departments are functionally interconnected. This is achieved by the following mechanism. With the accumulation of carbon dioxide, the inspiratory section of the respiratory center is excited, from which information goes to the pneumatic section of the center, then to its expiratory section. The latter, in addition, is excited by a whole range of reflex acts (from the receptors of the lungs, diaphragm, intercostal muscles, respiratory tract, vascular chemoreceptors). Due to its excitation through a special inhibitory reticular neuron, the activity of the inhalation center is inhibited and it is replaced by exhalation. Since the inhalation center is inhibited, it does not send further impulses to the pneumotoxic department, and the flow of information to the exhalation center stops from it. By this moment, carbon dioxide accumulates in the blood and the inhibitory influences from the expiratory department of the respiratory center are removed. As a result of this redistribution of the flow of information, the inhalation center is excited and the inhalation replaces the exhalation. And everything repeats again.

An important element in the regulation of respiration is the vagus nerve. It is through its fibers that the main influences on the center of exhalation go. Therefore, in the event of damage to it (as well as in case of damage to the pneumatic department of the respiratory center), breathing changes so that the inhalation remains normal, and the exhalation is sharply delayed. This type of breathing is called vagus dyspnea.

We have already noted above that when climbing to a height, there is an increase in pulmonary ventilation due to stimulation of chemoreceptors in the vascular zones. At the same time, the heart rate and MO increase. These reactions somewhat improve oxygen transport in the body, but not for long. Therefore, during a long stay in the mountains, as one adapts to chronic hypoxia, the initial (urgent) reactions of breathing gradually give way to a more economical adaptation of the body's gas transport system. Thus, in permanent residents of high altitudes, the reaction of breathing to hypoxia is sharply weakened ( hypoxic deafness) and pulmonary ventilation is maintained at almost the same level as that of those living on the plain. But with a long stay in high altitude conditions, VC increases, KEK increases, more myoglobin becomes in the muscles, and the activity of enzymes that provide biological oxidation and glycolysis increases in mitochondria. In people living in the mountains, in addition, the sensitivity of body tissues, in particular the central nervous system, to an insufficient supply of oxygen is reduced.

At altitudes above 12,000 m, the air pressure is very low, and under these conditions, even breathing pure oxygen does not solve the problem. Therefore, when flying at this altitude, airtight cabins (airplanes, spaceships) are necessary.

A person sometimes has to work in conditions of high pressure (diving). At depth, nitrogen begins to dissolve in the blood, and when it rises quickly from the depth, it does not have time to be released from the blood, gas bubbles cause vascular embolism. The resulting state is called decompression sickness. It is accompanied by pain in the joints, dizziness, shortness of breath, loss of consciousness. Therefore, nitrogen in air mixtures is replaced by insoluble gases (for example, helium).

A person can arbitrarily hold his breath for no more than 1-2 minutes. After preliminary hyperventilation of the lungs, this breath holding increases to 3-4 minutes. However, prolonged, for example, diving after hyperventilation is fraught with serious danger. A rapid drop in blood oxygenation can cause a sudden loss of consciousness, and in this state a swimmer (even an experienced one), under the influence of a stimulus caused by an increase in the partial tension of carbon dioxide in the blood, can inhale water and choke (drown).

So, in conclusion of the lecture, I must remind you that healthy breathing is through the nose, as rarely as possible, with a delay during inhalation and, especially, after it. Lengthening breath, we stimulate the work of the sympathetic division of the autonomic nervous system, with all the ensuing consequences. By lengthening the exhalation, we retain more and longer carbon dioxide in the blood. And this has a positive effect on the tone of blood vessels (reduces it), with all the ensuing consequences. Due to this, oxygen in such a situation can pass into the most distant microcirculation vessels, preventing the disruption of their function and the development of numerous diseases. Proper breathing is the prevention and treatment of a large group of diseases not only of the respiratory system, but also of other organs and tissues! Breathe in health!

The breathing reflex is the coordination of bones, muscles, and tendons to produce breathing. It often happens that we have to breathe against our body when we do not get the right amount of air. The space between the ribs (intercostal space) and the interosseous muscles are not as mobile as they should be in many people. The breathing process is a complex process that involves the entire body.

There are several respiratory reflexes:

Decay reflex - activation of breathing as a result of the collapse of the alveoli.

The inflation reflex is one of the many neural and chemical mechanisms that regulate breathing and is manifested through the stretch receptors of the lungs.

Paradoxical reflex - random deep breaths that dominate normal breathing, possibly associated with irritation of receptors in the initial phases of the development of microatelectasis.

Pulmonary vascular reflex - superficial tachypnea in combination with hypertension of the pulmonary circulation.

Irritation reflexes - cough reflexes that occur when subepithelial receptors in the trachea and bronchi are irritated and manifested by reflex closure of the glottis and bronchospasm; sneeze reflexes - a reaction to irritation of the nasal mucosa; change in the rhythm and nature of breathing when irritated by pain and temperature receptors.

The activity of neurons of the respiratory center is strongly influenced by reflex effects. There are permanent and non-permanent (episodic) reflex influences on the respiratory center.

Constant reflex influences arise as a result of irritation of the alveolar receptors (Goering-Breuer reflex), the root of the lung and pleura (pulmo-thoracic reflex), chemoreceptors of the aortic arch and carotid sinuses (Heymans reflex - approx. site), mechanoreceptors of these vascular areas, proprioreceptors of the respiratory muscles.

The most important reflex of this group is the Hering-Breuer reflex. The alveoli of the lungs contain stretch and contraction mechanoreceptors, which are sensitive nerve endings of the vagus nerve. Stretch receptors are excited during normal and maximum inspiration, i.e. any increase in the volume of the pulmonary alveoli excites these receptors. Collapse receptors become active only in pathological conditions (with maximum alveolar collapse).

In experiments on animals, it has been established that with an increase in the volume of the lungs (blowing air into the lungs), a reflex exhalation is observed, while pumping air out of the lungs leads to a rapid reflex inhalation. These reactions did not occur during transection of the vagus nerves. Consequently, nerve impulses enter the central nervous system through the vagus nerves.

The Hering-Breuer reflex refers to the mechanisms of self-regulation of the respiratory process, providing a change in the acts of inhalation and exhalation. When the alveoli are stretched during inhalation, nerve impulses from stretch receptors along the vagus nerve go to expiratory neurons, which, when excited, inhibit the activity of inspiratory neurons, which leads to passive exhalation. The pulmonary alveoli collapse and the nerve impulses from the stretch receptors no longer reach the expiratory neurons. Their activity falls, which creates conditions for increasing the excitability of the inspiratory part of the respiratory center and active inspiration. In addition, the activity of inspiratory neurons increases with an increase in the concentration of carbon dioxide in the blood, which also contributes to the implementation of the act of inhalation.

Thus, self-regulation of respiration is carried out on the basis of the interaction of the nervous and humoral mechanisms of regulation of the activity of neurons of the respiratory center.

Pulmotoraccular reflex occurs when the receptors embedded in the lung tissue and pleura are excited. This reflex appears when the lungs and pleura are stretched. The reflex arc closes at the level of the cervical and thoracic segments of the spinal cord. The end effect of the reflex is a change in the tone of the respiratory muscles, due to which there is an increase or decrease in the average volume of the lungs.
Nerve impulses from the proprioreceptors of the respiratory muscles constantly go to the respiratory center. During inhalation, the proprioreceptors of the respiratory muscles are excited and nerve impulses from them arrive at the inspiratory neurons of the respiratory center. Under the influence of nerve impulses, the activity of inspiratory neurons is inhibited, which contributes to the onset of exhalation.

Intermittent reflex influences on the activity of respiratory neurons are associated with the excitation of extero- and interoreceptors of various functions. Intermittent reflex effects that affect the activity of the respiratory center include reflexes that occur when receptors of the mucous membrane of the upper respiratory tract, nose, nasopharynx, temperature and pain receptors of the skin, proprioreceptors of skeletal muscles, and interoreceptors are irritated. So, for example, with the sudden inhalation of ammonia vapor, chlorine, sulfur dioxide, tobacco smoke and some other substances, irritation of the receptors of the mucous membrane of the nose, pharynx, larynx occurs, which leads to reflex spasm of the glottis, and sometimes even bronchial muscles and reflex breath holding.

When the epithelium of the respiratory tract is irritated by accumulated dust, mucus, as well as chemical irritants and foreign bodies, sneezing and coughing are observed. Sneezing occurs when the receptors of the nasal mucosa are irritated, and coughing occurs when the receptors of the larynx, trachea, and bronchi are excited.

Protective respiratory reflexes (coughing, sneezing) occur when the mucous membranes of the respiratory tract are irritated. When ammonia enters, respiratory arrest occurs and the glottis is completely blocked, the lumen of the bronchi narrows reflexively.

Irritation of temperature receptors of the skin, in particular cold ones, leads to reflex breath holding. Excitation of pain receptors in the skin, as a rule, is accompanied by an increase in respiratory movements.

Excitation of proprioceptors of skeletal muscles causes stimulation of the act of breathing. The increased activity of the respiratory center in this case is an important adaptive mechanism that provides for the increased needs of the body for oxygen during muscular work.
Irritation of interoreceptors, such as mechanoreceptors of the stomach when it is stretched, leads to inhibition of not only cardiac activity, but also respiratory movements.

When the mechanoreceptors of the vascular reflexogenic zones (aortic arch, carotid sinuses) are excited, changes in the activity of the respiratory center are observed as a result of changes in blood pressure. Thus, an increase in blood pressure is accompanied by a reflex delay in breathing, a decrease leads to stimulation of respiratory movements.

Thus, the neurons of the respiratory center are extremely sensitive to influences that cause excitation of extero-, proprio-, and interoreceptors, which leads to a change in the depth and rhythm of respiratory movements in accordance with the conditions of the organism's vital activity.

The activity of the respiratory center is influenced by the cerebral cortex. The regulation of respiration by the cerebral cortex has its own qualitative features. In experiments with direct stimulation of individual areas of the cerebral cortex by electric current, a pronounced effect on the depth and frequency of respiratory movements was shown. The results of studies by M. V. Sergievsky and his collaborators, obtained by direct stimulation of various parts of the cerebral cortex with electric current in acute, semi-chronic and chronic experiments (implanted electrodes), indicate that cortical neurons do not always have an unambiguous effect on respiration. The final effect depends on a number of factors, mainly on the strength, duration and frequency of the applied stimuli, the functional state of the cerebral cortex and the respiratory center.

To assess the role of the cerebral cortex in the regulation of respiration, data obtained using the method of conditioned reflexes are of great importance. If in humans or animals the sound of a metronome is accompanied by inhalation of a gas mixture with a high content of carbon dioxide, this will lead to an increase in pulmonary ventilation. After 10 ... 15 combinations, the isolated activation of the metronome (conditional signal) will cause stimulation of respiratory movements - a conditioned respiratory reflex has formed for a selected number of metronome beats per unit time.

The increase and deepening of breathing, which occur before the start of physical work or sports, are also carried out according to the mechanism of conditioned reflexes. These changes in respiratory movements reflect shifts in the activity of the respiratory center and have an adaptive value, helping to prepare the body for work that requires a lot of energy and increased oxidative processes.

According to M.E. Marshak, cortical: the regulation of breathing provides the necessary level of pulmonary ventilation, the rate and rhythm of breathing, the constancy of the level of carbon dioxide in the alveolar air and arterial blood.
The adaptation of respiration to the external environment and the shifts observed in the internal environment of the body is associated with extensive nervous information entering the respiratory center, which is pre-processed, mainly in the neurons of the brain bridge (pons varolii), midbrain and diencephalon and in the cells of the cerebral cortex .

The activity of neurons of the respiratory center is strongly influenced by reflex effects. There are permanent and non-permanent (episodic) reflex influences on the respiratory center.

Constant reflex influences arise as a result of irritation of the alveolar receptors (Goering-Breuer reflex), the root of the lung and pleura (pneumothorax reflex), chemoreceptors of the aortic arch and carotid sinuses (Heimans reflex), mechanoreceptors of these vascular areas, proprioceptors of the respiratory muscles.

Thus, self-regulation of respiration is carried out on the basis of the interaction of the nervous and humoral mechanisms of regulation of the activity of neurons of the respiratory center.

Nerve impulses from the proprioreceptors of the respiratory muscles constantly go to the respiratory center. During inhalation, the proprioreceptors of the respiratory muscles are excited and nerve impulses from them arrive at the inspiratory neurons of the respiratory center. Under the influence of nerve impulses, the activity of inspiratory neurons is inhibited, which contributes to the onset of exhalation.

Intermittent reflex influences on the activity of respiratory neurons are associated with the excitation of extero- and interoreceptors of various functions.

Intermittent reflex effects that affect the activity of the respiratory center include reflexes that occur when receptors of the mucous membrane of the upper respiratory tract, nose, nasopharynx, temperature and pain receptors of the skin, proprioreceptors of skeletal muscles, and interoreceptors are irritated. So, for example, with the sudden inhalation of ammonia vapor, chlorine, sulfur dioxide, tobacco smoke and some other substances, irritation of the receptors of the mucous membrane of the nose, pharynx, larynx occurs, which leads to reflex spasm of the glottis, and sometimes even bronchial muscles and reflex breath holding.

Coughing and sneezing begin with a deep breath that occurs reflexively. Then there is a spasm of the glottis and at the same time an active exhalation. As a result, the pressure in the alveoli and airways increases significantly. The subsequent opening of the glottis leads to the release of air from the lungs with a push into the airways and out through the nose (when sneezing) or through the mouth (when coughing). Dust, mucus, foreign bodies are carried away by this air stream and are thrown out of the lungs and respiratory tract.

Coughing and sneezing under normal conditions are classified as protective reflexes. These reflexes are called protective because they prevent harmful substances from entering the respiratory tract or contribute to their removal.

Irritation of interoreceptors, such as mechanoreceptors of the stomach during its stretching, leads to inhibition of not only cardiac activity, but also respiratory movements.

Important facts were established by E. A. Asratyan and his collaborators. It was found that in animals with a removed cerebral cortex, there were no adaptive reactions of external respiration to changes in living conditions. Thus, muscle activity in such animals was not accompanied by stimulation of respiratory movements, but led to prolonged shortness of breath and respiratory discoordination.

To assess the role of the cerebral cortex in the regulation of respiration, data obtained using the method of conditioned reflexes are of great importance. If in humans or animals the sound of a metronome is accompanied by inhalation of a gas mixture with a high content of carbon dioxide, this will lead to an increase in pulmonary ventilation. After 10 ... 15 combinations, the isolated inclusion of the metronome (conditional signal) will cause stimulation of respiratory movements - a conditioned respiratory reflex has formed for a selected number of metronome beats per unit time.

The adaptation of respiration to the external environment and the shifts observed in the internal environment of the body is associated with extensive nervous information entering the respiratory center, which is pre-processed, mainly in the neurons of the brain bridge (pons varolii), midbrain and diencephalon and in the cells of the cerebral cortex .

Thus, the regulation of the activity of the respiratory center is complex. According to M.V. Sergievsky, it consists of three levels.

The first level of regulation is represented by the spinal cord. Here are the centers of the phrenic and intercostal nerves. These centers cause contraction of the respiratory muscles. However, this level of respiratory regulation cannot provide a rhythmic change in the phases of the respiratory cycle, since a huge number of afferent impulses from the respiratory apparatus, bypassing the spinal cord, are sent directly to the medulla oblongata.

The second level of regulation is associated with the functional activity of the medulla oblongata. Here is the respiratory center, which perceives a variety of afferent impulses coming from the respiratory apparatus, as well as from the main reflexogenic vascular zones. This level of regulation provides a rhythmic change in the phases of respiration and the activity of spinal motor neurons, the axons of which innervate the respiratory muscles.

The third level of regulation is the upper parts of the brain, including cortical neurons. Only in the presence of the cerebral cortex is it possible to adequately adapt the reactions of the respiratory system to the changing conditions of the organism's existence.

The airways are divided into upper and lower. The upper ones include the nasal passages, nasopharynx, the lower larynx, trachea, bronchi. The trachea, bronchi and bronchioles are the conduction zone of the lungs. The terminal bronchioles are called the transition zone. They have a small number of alveoli, which contribute little to gas exchange. The alveolar ducts and alveolar sacs belong to the exchange zone.

Physiological is nasal breathing. When cold air is inhaled, a reflex expansion of the vessels of the nasal mucosa and a narrowing of the nasal passages occur. This contributes to better heating of the air. Its hydration occurs due to moisture secreted by the glandular cells of the mucosa, as well as lacrimal moisture and water filtered through the capillary wall. Purification of the air in the nasal passages occurs due to the deposition of dust particles on the mucosa.

Protective respiratory reflexes occur in the airways. When inhaling air containing irritating substances, there is a reflex slowdown and a decrease in the depth of breathing. At the same time, the glottis narrows and the smooth muscles of the bronchi contract. When the irritant receptors of the epithelium of the mucous membrane of the larynx, trachea, bronchi are stimulated, impulses from them arrive along the afferent fibers of the upper laryngeal, trigeminal and vagus nerves to the inspiratory neurons of the respiratory center. There is a deep breath. Then the muscles of the larynx contract and the glottis closes. Expiratory neurons are activated and exhalation begins. And since the glottis is closed, the pressure in the lungs increases. At a certain moment, the glottis opens and air leaves the lungs at high speed. There is a cough. All these processes are coordinated by the cough center of the medulla oblongata. When dust particles and irritating substances are exposed to the sensitive endings of the trigeminal nerve, which are located in the nasal mucosa, sneezing occurs. Sneezing also initially activates the inspiratory center. Then there is a forced exhalation through the nose.

There are anatomical, functional and alveolar dead space. Anatomical is the volume of the airways - the nasopharynx, larynx, trachea, bronchi, bronchioles. It does not undergo gas exchange. Alveolar dead space refers to the volume of alveoli that are not ventilated or there is no blood flow in their capillaries. Therefore, they also do not participate in gas exchange. Functional dead space is the sum of anatomical and alveolar. In a healthy person, the volume of alveolar dead space is very small. Therefore, the size of the anatomical and functional spaces is almost the same and is about 30% of the respiratory volume. On average 140 ml. In violation of ventilation and blood supply to the lungs, the volume of functional dead space is much larger than the anatomical one. At the same time, the anatomical dead space plays an important role in the processes of respiration. The air in it is warmed, humidified, cleaned of dust and microorganisms. Here respiratory protective reflexes are formed - coughing, sneezing. It senses smells and produces sounds.

Details

The nervous system usually sets such alveolar ventilation rate, which almost exactly corresponds to the needs of the body, so the tension of oxygen (Po2) and carbon dioxide (Pco2) in arterial blood changes little even during heavy physical exertion and during most other cases of respiratory stress. This article sets out neurogenic system function breathing regulation.

Anatomy of the respiratory center.

respiratory center consists of several groups of neurons located in the brainstem on both sides of the medulla oblongata and the bridge. They are divided into three large groups of neurons:

dorsal group of respiratory neurons, located in the dorsal part of the medulla oblongata, which mainly causes inspiration;
ventral group of respiratory neurons, which is located in the ventrolateral part of the medulla oblongata and mainly causes exhalation;
pneumotaxic center, which is located dorsally at the top of the pons and controls mainly the rate and depth of breathing. The most important role in the control of breathing is performed by the dorsal group of neurons, so we will consider its functions first.

Dorsal group respiratory neurons extends for most of the length of the medulla oblongata. Most of these neurons are located in the nucleus of the solitary tract, although additional neurons located in the nearby reticular formation of the medulla oblongata are also important for the regulation of respiration.

The solitary tract nucleus is the sensory nucleus for wandering and glossopharyngeal nerves, which transmit sensory signals to the respiratory center from:

peripheral chemoreceptors;
baroreceptors;
various types of lung receptors.

Generation of respiratory impulses. Breathing rhythm.

Rhythmic inspiratory discharges from the dorsal group of neurons.

Basic breathing rhythm generated mainly by the dorsal group of respiratory neurons. Even after transection of all peripheral nerves entering the medulla oblongata and the brainstem below and above the medulla oblongata, this group of neurons continues to generate repetitive bursts of inspiratory neuron action potentials. The underlying cause of these volleys is unknown.

After some time, the activation pattern is repeated, and this continues throughout the life of the animal, so most physiologists involved in the physiology of respiration believe that humans also have a similar network of neurons located within the medulla oblongata; it is possible that it includes not only the dorsal group of neurons, but also adjacent parts of the medulla oblongata, and that this network of neurons is responsible for the main rhythm of breathing.

Increasing inspiration signal.

Signal from neurons that is transmitted to the inspiratory muscles, in the main diaphragm, is not an instantaneous burst of action potentials. During normal breathing gradually increases for about 2 sec. After that he drops sharply for about 3 seconds, which stops the excitation of the diaphragm and allows the elastic traction of the lungs and chest wall to exhale. Then the inspiratory signal starts again, and the cycle repeats again, and in the interval between them there is an exhalation. Thus, the inspiratory signal is an increasing signal. Apparently, such an increase in the signal provides a gradual increase in lung volume during inspiration instead of a sharp inspiration.

Two moments of the rising signal are controlled.

The rate of increase of the rising signal, so during difficult breathing, the signal rises quickly and causes rapid filling of the lungs.
The limiting point at which the signal suddenly disappears. This is a common way to control the rate of breathing; the sooner the rising signal stops, the shorter the inspiratory time. At the same time, the duration of exhalation is also reduced, as a result, breathing quickens.

Reflex regulation of breathing.

Reflex regulation of breathing is carried out due to the fact that the neurons of the respiratory center have connections with numerous mechanoreceptors of the respiratory tract and alveoli of the lungs and receptors of vascular reflexogenic zones. The following types of mechanoreceptors are found in the human lungs:

irritant, or rapidly adapting, respiratory mucosal receptors;
Stretch receptors of smooth muscles of the respiratory tract;
J-receptors.

Reflexes from the mucous membrane of the nasal cavity.

Irritation of irritant receptors of the nasal mucosa, for example, tobacco smoke, inert dust particles, gaseous substances, water causes narrowing of the bronchi, glottis, bradycardia, decreased cardiac output, narrowing of the lumen of the vessels of the skin and muscles. The protective reflex is manifested in newborns during short-term immersion in water. They experience respiratory arrest, preventing the penetration of water into the upper respiratory tract.

Reflexes from the throat.

Mechanical irritation of the mucosal receptors of the back of the nasal cavity causes a strong contraction of the diaphragm, external intercostal muscles, and, consequently, inhalation, which opens the airway through the nasal passages (aspiration reflex). This reflex is expressed in newborns.

Reflexes from the larynx and trachea.

Numerous nerve endings are located between the epithelial cells of the mucous membrane of the larynx and main bronchi. These receptors are irritated by inhaled particles, irritating gases, bronchial secretions, and foreign bodies. All this calls cough reflex, manifested in a sharp exhalation against the background of narrowing of the larynx and contraction of the smooth muscles of the bronchi, which persists for a long time after the reflex.
The cough reflex is the main pulmonary reflex of the vagus nerve.

Reflexes from bronchiole receptors.

Numerous myelinated receptors are found in the epithelium of the intrapulmonary bronchi and bronchioles. Irritation of these receptors causes hyperpnea, bronchoconstriction, contraction of the larynx, hypersecretion of mucus, but is never accompanied by cough. Receptors most sensitive to three types of stimuli:

tobacco smoke, numerous inert and irritating chemicals;
damage and mechanical stretching of the airways during deep breathing, as well as pneumothorax, atelectasis, the action of bronchoconstrictors;
pulmonary embolism, pulmonary capillary hypertension and pulmonary anaphylactic phenomena.

Reflexes from J-receptors.

in the alveolar septa in contact with capillaries specific J receptors. These receptors are especially susceptible to interstitial edema, pulmonary venous hypertension, microembolism, irritating gases and inhalation narcotic substances, phenyl diguanide (with intravenous administration of this substance).

Stimulation of J-receptors causes first apnea, then superficial tachypnea, hypotension and bradycardia.

Hering-Breuer reflex.

Inflation of the lungs in an anesthetized animal reflexively inhibits inhalation and causes exhalation.. Transection of the vagus nerves eliminates the reflex. Nerve endings located in the bronchial muscles act as receptors for lung stretch. They are referred to as slowly adapting lung stretch receptors, which are innervated by myelinated fibers of the vagus nerve.

Hering-Breuer reflex controls the depth and frequency of breathing. In humans, it has physiological significance at respiratory volumes over 1 liter (for example, during physical activity). In an awake adult, short-term bilateral vagus nerve block with local anesthesia does not affect either the depth or the rate of breathing.
In newborns, the Hering-Breuer reflex is clearly manifested only in the first 3-4 days after birth.

Proprioceptive breath control.

The receptors of the chest joints send impulses to the cerebral cortex and are the only source of information about chest movements and tidal volumes.

The intercostal muscles, to a lesser extent the diaphragm, contain a large number of muscle spindles.. The activity of these receptors is manifested during passive muscle stretching, isometric contraction and isolated contraction of intrafusal muscle fibers. Receptors send signals to the corresponding segments of the spinal cord. Insufficient shortening of the inspiratory or expiratory muscles increases the impulse from the muscle spindles, which dose the muscle effort through the motor neurons.

Chemoreflexes of breathing.

Partial pressure of oxygen and carbon dioxide(Po2 and Pco2) in the arterial blood of humans and animals is maintained at a fairly stable level, despite significant changes in O2 consumption and CO2 release. Hypoxia and decrease in blood pH ( acidosis) cause increased ventilation(hyperventilation), and hyperoxia and increased blood pH ( alkalosis) - decrease in ventilation(hypoventilation) or apnea. Control over the normal content in the internal environment of the body of O2, CO2 and pH is carried out by peripheral and central chemoreceptors.

adequate stimulus for peripheral chemoreceptors is decrease in arterial blood Po2, to a lesser extent, an increase in Pco2 and pH, and for central chemoreceptors - an increase in the concentration of H + in the extracellular fluid of the brain.

Arterial (peripheral) chemoreceptors.

Peripheral chemoreceptors found in carotid and aortic bodies. Signals from arterial chemoreceptors through the carotid and aortic nerves initially arrive at the neurons of the nucleus of the single bundle of the medulla oblongata, and then switch to the neurons of the respiratory center. The response of peripheral chemoreceptors to a decrease in Pao2 is very rapid, but non-linear. With Pao2 within 80-60 mm Hg. (10.6-8.0 kPa) there is a slight increase in ventilation, and when Pao2 is below 50 mm Hg. (6.7 kPa) there is a pronounced hyperventilation.

Paco2 and blood pH only potentiate the effect of hypoxia on arterial chemoreceptors and are not adequate irritants for this type of respiratory chemoreceptors.
Response of arterial chemoreceptors and respiration to hypoxia. Lack of O2 in arterial blood is the main irritant of peripheral chemoreceptors. Impulse activity in the afferent fibers of the carotid sinus nerve stops when Pao2 is above 400 mm Hg. (53.2 kPa). With normoxia, the frequency of discharges of the carotid sinus nerve is 10% of their maximum response, which is observed at Pao2 of about 50 mm Hg. and below. The hypoxic respiration reaction is practically absent in the indigenous inhabitants of the highlands and disappears approximately 5 years later in the inhabitants of the plains after the beginning of their adaptation to the highlands (3500 m and above).

central chemoreceptors.

The location of the central chemoreceptors has not been definitively established. Researchers believe that such chemoreceptors are located in the rostral regions of the medulla oblongata near its ventral surface, as well as in various zones of the dorsal respiratory nucleus.
The presence of central chemoreceptors is proved quite simply: after transection of the sinocarotid and aortic nerves in experimental animals, the sensitivity of the respiratory center to hypoxia disappears, but the respiratory response to hypercapnia and acidosis is completely preserved. Transection of the brainstem directly above the medulla oblongata does not affect the nature of this reaction.

adequate stimulus for central chemoreceptors is change in the concentration of H * in the extracellular fluid of the brain. The function of a regulator of threshold pH shifts in the region of central chemoreceptors is performed by the structures of the blood-brain barrier, which separates blood from the extracellular fluid of the brain. O2, CO2, and H+ are transported through this barrier between the blood and the extracellular fluid of the brain. The transport of CO2 and H+ from the internal environment of the brain into the blood plasma through the structures of the blood-brain barrier is regulated by the enzyme carbonic anhydrase.
Breathing response to CO2. Hypercapnia and acidosis stimulate, while hypocapnia and alkalosis inhibit central chemoreceptors.