Medullary chemoreceptors are sensitive to ?
Ans. is 'a' i.e., H+ in CSFThe primary direct stimulus for central chemoreceptors is increased H+ concentration in the CSF and brain interstitial fluid.Central chemoreceptors These receptors are located in a chemosensitive area on the ventral surface of the medulla near the exit of the ninth and tenth cranial nerves. The primary stimulus for the central chemoreceptors is an increase in the hydrogen ion concentration. Stimulation of central chemoreceptors by increased hydrogen ion concentration leads to excitation of the respiratory neurons, thereby producing an increase in the rate and depth of respiration.Although the primary stimulus for central chemoreceptors is an increase in hydrogen ion concentration, in actual practice the physiological stimulus is an increase in PCO2. The reason is that hydrogen ions cannot cross blood - brain barrier. Therefore, a change in the blood hydrogen ion concentration does not change the hydrogen ion concentration in the immediate vicinity of the chemosensitive neurons (i.e., in CSF and brain interstitial fluid). On the other hand, CO2 being lipid soluble can easily cross blood brain barrier. It enters the brain, where it is hydrated to give rise to fr and HCO2- ions. Now these H' directly stimulate the central chemoreceptors.Thus, central chemoreceptors are directly stimulated by an increase in H+ concentration in CSF and brain inerstitial tissue, which is brought about by change in aerial PCO2 (PaCO2).
H+ in CSF
CO2 in CSF
H+ in blood
CO2 in blood