A PNEUSTIC AND PNEUMOTAXIC CENTRES :::
The rhythmic discharge of the neurons in the respiratory centre is spontaneous but it is modifed by centres in the pons and afferent impulses coming from lungs through vagus nerve Afferent impulses are initiated by the distension of the air sacs (stretch receptors) or stimulation of chemoreceptors of the aortic body carotid body and medulla oblongata itself They are carried out by the vagus nerves to the respiratory centres in medulla oblongata these impulses can directly stimulate inspiratory centres or influence these centres by higher centres (apneustic or pneumotaxic centre ) Besides these important factors coughing sneezing swallowing and skin stimulation also reflexly affect respiration Even active movement of muscles and joints especially of intercostal abdominal and diaphragmatic muscles stimulate respiration
Pons in the brain consists of two more centres apneustic centre and pneumotaxic centre stimulation of apneustic centre stimulates respiratory centres and results in arrest of respiration in inspiration pneumotaxic centre which is situated above the apneustic centre has inhibitory influence on the apneustic centre and prevents the inspiratory arrest Apneustic centres also cause deep and prolonged inspiration
chemical control:: it is the main factor in regulating the rate and depth or respiration The pneumotaxic centre in the pons is affected by the reaction of the blood carbon dioxide also stimulates the respiratory centre directly the pneumotanic centers receive information about the changes in CO2 through chemoreceptors present in the arch of aorta and the carotid body
Chemical regulation is affected mainly by change in CO2 tension the respiratory centre being extremely sensitive to it increase in CO2 Concentration increases the acidity of the blood and acts as a stimulus par excellence to respiration very high increase may however cause asphyxia and even death with O2 it is reversed lack of oxygen stimulates respiration to compensate oxygenation if decrease in O2 is beyond limit it will result in cyanosis and even death Excess of O2 does not produce harm but pure O2 breathed for a very long time can cause a harm
under the influences of stimulatory effect of the arterial pCO2 and the tonic activity of the apneustic centre the inspiratory centre discharges impulses to respiratory muscles and inspiration follows meanwhile the inspiratory centre also sends the impulses to pneumotaxic centre which inturn discharges inhibitory impulses to the apneustic centre
Apneustic centre also gets its inhibitory impulses from the vagus nerve These impulses come from stretch receptors of the lung and chemoreceptors of aortic and carotid bodies Thus apneustic centre ceases to activate medullary centres and as a result the inspiratory centre stops discharging and the expiration follows passively
By regulating respiratory depth and rate through above mentioned centres respiratory system performs the following functions ::
1.Supply of adequate amount of oxgen and removal of carbon dioxide
2.Regulation of H+ ion concentration and hence pH of blood
3.Maintenance of body temperature
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