Regulation of respiration: Breathing is an involuntary action which is controlled by the nervous system. It is controlled by some groups of nerve cells located in the medulla oblongata and pons. These groups are called respiratory centres.
There are three main respiratory centres in the human brain:
1. Dorsal Respiratory Centre: This centre is located in the dorsal part of the medulla. This centre controls the state of normal rest. This centre sends repetitive inspiration signals to the muscles during normal breathing. Now a neural signal coming to the inspiratory muscles for about two seconds stimulates inspiration. After this it stops for about three seconds. Due to which the stimulation of end respiratory muscles also stops. Now the muscles become relaxed. Exhalation occurs due to elastic projection. This does not require any special stimulation. This is called respiratory rhythm which remains throughout life. This rhythm is also modified by many stimuli such as CO₂ and H+ ions. When the concentration of CO, increases, the chemoreceptors present in the carotid and aortic functions get stimulated. They send nerve impulses to the respiratory centre. The signal for contraction at a higher rate is transmitted from the inspiratory centre to the expiratory muscles. This increases the rate of respiration and increase in H+ ion concentration also stimulates chemoreceptors and increases the rate of respiration. Inflated lungs send signals to the expiratory centre via the Vagus nerve. After exhalation, the stimulation of receptors ceases, as a result of which the expiratory centres become inactive.
2. Pneumotaxic Center: It is located in the pons. It stops inhalation and stimulates exhalation. Signals from this centre are sent to the respiratory centre. When signals from the pneumotaxic centre reach the inspiratory centre, the signals from the inspiratory centre stop. When the signals from the pneumotaxic centre are strong, inspiration occurs only for a very short period (about 0.5 seconds). Therefore, the lungs are filled only partially. When the signals are weak, inspiration continues for 5 seconds or more, so the lungs are completely filled. In this way the pneumotaxic centre controls the duration of inspiration and the filling of the lungs. Its powerful signals increase the respiratory rate.
3. Venteral Respiratory Center: This centre is also located in the medulla. This centre, which is inactive during normal calm breathing, controls the increased needs of pulmonary ventilation during exercise etc. by influencing the processes of inhalation and exhalation.