The respiratory areas of the medulla oblongata and pons are influenced by a number of factors that cause modifications in the rate and depth of breathing. Factors involved in involuntary control are detected by sensory receptors, which forward nerve impulses to the DRG. Higher brain centers involved in voluntary control send nerve impulses to the pontine respiratory group, which then transmits nerve impulses to the respiratory rhythmicity center.
The most important chemical factors affecting respiration are the concentrations of CO2, H+, and O2 in the blood or cerebrospinal fluid. Sensory receptors that are sensitive to these factors are called chemoreceptors. The chemoreceptors in the medulla oblongata are sensitive to increases in H+ and CO2 in the cerebrospinal fluid. The chemoreceptors in the carotid bodies and aortic bodies are sensitive to changes in CO2, H+, and O2 , The carotid bodies are located in the walls of external carotid arteries, while aortic bodies are located in the aortic arch. You can see that they are strategically located, especially to monitor blood going to the brain.
You may wonder why the concentration of H+ is involved in respiratory control. The mechanism for transporting CO2 in the blood releases H+ as a by-product. Therefore, an increase in CO2 concentration produces an increase in the H+ concentration.
If the concentrations of CO2 and H+ in the blood or CSF increase, the DRG relays the information so that the VRG is stimulated to increase the rate and depth of breathing, which increases the rate of CO2 and H+ removal and returns their concentrations to normal resting levels. Once homeostasis is restored, the rate and depth of breathing also return to normal quiet levels.
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