 This video will cover the following objective from respiratory physiology, outline the mechanisms behind the control of breathing, describe the respiratory centers of the medulla oblongata, describe the respiratory centers of the pons. Pulmonary ventilation is normally regulated subconsciously with an involuntary mechanism coordinated by respiratory control centers of the brainstem. These control centers are found specifically within the medulla oblongata and the pons. Within the medulla oblongata there are two regions, the dorsal respiratory group and the ventral respiratory group that are the respiratory control centers. The dorsal respiratory group contains the cell bodies of the motor neurons that extend their axons out through the spinal nerves that stimulate contraction of the diaphragm and the external intercostal muscles, leading to inspiration. The ventral respiratory group contains a cluster of neurons known as the pre-Botsinger complex that generates the breathing rhythm to regulate the activity of the dorsal respiratory group. The ventral respiratory group also contains motor neurons that excite contraction of accessory respiratory muscles, for example the internal intercostal muscles are accessory muscles of expiration that contract to produce more forceful expirations. The respiratory control centers in the medulla oblongata are in turn regulated by respiratory control centers in the pons known as the abnustic and pneumotastic centers. The abnustic center excites the dorsal respiratory group stimulating an increased respiratory drive and the pneumotastic center has an inhibitory effect decreasing the respiratory drive. The respiratory control centers of the brainstem are also regulated by the cerebral cortex enabling voluntary control over the respiratory muscles. The hypothalamus also contains control centers that can influence pulmonary ventilation enabling emotions to have an influence over pulmonary ventilation such as when anger causes a cessation of ventilation or when anxiety causes hyperventilation. As the major functions of the respiratory system include maintenance of the acid-base balance of the body or maintenance of the pH of the body there are central chemoreceptors in the medulla oblongata that are very sensitive to changes in the pH of the cerebrospinal fluid and this is the primary mechanism controlling the respiratory drive which regulates the pulmonary ventilation rate. If the blood carbon dioxide concentration becomes elevated which is known as hypercapnia the carbon dioxide diffuses into the cerebrospinal fluid where it reacts with water in a reaction catalyzed by the enzyme carbonic anhydrase to form carbonic acid. Then carbonic acid releases hydrogen ions into solution lowering the pH of the cerebrospinal fluid. This decrease in pH is detected by the central chemoreceptors leading to an increased respiratory drive accumulating an increase in respiratory rate and or tidal volume increasing the pulmonary ventilation rate increasing the rate at which carbon dioxide is removed from the blood in order to restore the homeostatic set point of the cerebrospinal fluid pH. In response to low blood carbon dioxide concentration which is known as hypercapnia the pH of the cerebrospinal fluid will increase. The central chemoreceptors will respond to this increased pH by decreasing the respiratory drive leading to a decreased pulmonary ventilation rate in order to restore the homeostatic set point of the cerebrospinal fluid pH. There are also peripheral chemoreceptors located in the aortic arch parotid sinus near the location of the bororeceptors that monitor mean arterial pressure by detecting stretching of the large arteries. The peripheral chemoreceptors monitor the pH of the arterial blood carbon dioxide concentration and oxygen concentration of the arterial blood. While the central chemoreceptors provide the primary mechanism regulating pulmonary ventilation under normal circumstances in an abnormal circumstance such as at high altitude where the partial pressure of oxygen in the atmosphere is lower leading to a decreased rate of oxygen diffusion into the blood. A low oxygen concentration of the arterial blood known as hypoxia is detected by the peripheral chemoreceptors. Receptors in the carotid sinus relay this information in through cranial nerve number 9, the glasopharyngeal nerve, and chemoreceptors located in the arch of the aorta relay this information in through cranial nerve number 10, the vegas nerve. This information is relayed into the control centers in the medulla oblongata and leads to an increase in the pulmonary ventilation rate in order to restore the homeostatic set point for the blood oxygen concentration. This table summarizes the major factors influencing the pulmonary ventilation rate while the medullary respiratory centers include the ventral respiratory group and the dorsal respiratory group. It is the pre-botsager complex of neurons in the ventral respiratory group that generates the breathing rhythm. The ventral respiratory group also contains motor neurons that excite accessory muscles of respiration. The dorsal respiratory group contains the motor neurons that excite the primary muscles of inspiration, the diaphragm, and the external intercostal muscles. The dorsal respiratory group also receives sensory information from the chemoreceptors while the central chemoreceptor in the medulla oblongata provides the primary influence over the pulmonary ventilation rate under normal circumstances. The peripheral chemoreceptors in the aortic body of the aortic arch and the carotid body of the carotid sinus are monitoring the carbon dioxide and oxygen concentrations of the arterial blood as well as the pH of the arterial blood and relay that information into the dorsal respiratory group in order to influence the pulmonary ventilation rate. Under abnormal circumstances which lead to abnormally low oxygen concentration of the blood or abnormally high carbon dioxide and hydrogen ion concentrations of the arterial blood. The pontine respiratory groups are the pneumotastic and apnoistic centers that influence the medullary respiratory centers and the pontine respiratory groups are in turn regulated by control centers in the hypothalamus and cerebral cortex where the control centers of the hypothalamus enable emotions to influence the respiratory drive. The cerebral cortex enables voluntary control over the respiratory muscles. There are also receptors in the lungs that detect irritants like dust particles and in response to irritants these irritant receptors will relay information through the vagus nerve into the medulla oblongata stimulating protective reflexes like coughing and sneezing to clear the airway.