Breathing Regulation

The body's need for oxygen during rest and during work is not the same; therefore, the frequency and depth of breathing must automatically change to adapt to changing conditions. During muscular work, oxygen consumption by muscles and other tissues can increase 4-5 times. Breathing requires coordinated contraction of many individual muscles; this coordination is carried out by the respiratory center - a special group of cells located in one of the parts of the brain called the medulla oblongata.

From this center, volleys of impulses are rhythmically sent to the diaphragm and intercostal muscles, causing regular and coordinated contraction of the corresponding muscles every 4-5 seconds. Under normal conditions, breathing movements occur automatically, without control from our will. But when the nerves going to the diaphragm (phrenic nerves) and intercostal muscles are cut or damaged (for example, in infantile paralysis), breathing movements immediately stop.

Of course, a person can arbitrarily change the frequency and depth of breathing; he may even not breathe at all for some time, but he is not able to hold his breath for such a long time that it would cause any significant harm: the automatic mechanism comes into action and causes inhalation. The question naturally arises: why does the respiratory center periodically send volleys of impulses? Through a series of experiments, it was found that if the connections of the respiratory center with all other parts of the brain are interrupted, that is, if the sensory nerves and pathways coming from the higher brain centers are cut, then the respiratory center sends a continuous stream of impulses and the muscles involved in breathing , having contracted, remain in a contracted state.

Thus, the respiratory center, left to its own devices, causes complete contraction of the muscles involved in breathing. If, however, either the sensory nerves or the pathways coming from the higher brain centers remain intact, then the respiratory movements continue to occur normally. This means that normal breathing requires periodic inhibition of the respiratory center so that it stops sending impulses that cause muscle contraction.

Further experiments showed that the pneumotaxic center, located in the midbrain (Fig. :, 268), together with the respiratory center, form a “reverberating circular path”, which serves as the basis for regulating the respiratory rate.

In addition, stretching the walls of the alveoli during inhalation stimulates the pressure-sensitive nerve cells located in these walls, and these cells send impulses to the brain that inhibit the respiratory center, which leads to exhalation. The respiratory center is also stimulated or inhibited by impulses coming to it along many other nerve pathways. Severe pain in any part of the body causes a reflex increase in breathing.

In addition, in the mucous membrane of the larynx and pharynx there are receptors that, when irritated, send impulses to the respiratory center that inhibit breathing. These are important safety devices. When any irritating gas, such as ammonia or strong acid vapors, enters the respiratory tract, it stimulates the receptors in the larynx, which send inhibitory impulses to the respiratory center, and we involuntarily “take our breath away”; Thanks to this, the harmful substance does not penetrate into the lungs.

In the same way, when food accidentally enters the larynx, it irritates the receptors in the mucous membrane of this organ, causing them to send inhibitory impulses to the respiratory center. Breathing instantly stops, and food does not enter the lungs, where it could damage the delicate epithelium. During muscular work, the frequency and depth of breathing must increase to satisfy the body's increased need for oxygen and prevent the accumulation of carbon dioxide.

The concentration of carbon dioxide in the blood is the main factor regulating respiration. Increased coal content