Chemoreceptors in the Medulla

The chemoreceptors most sensitive to changes in the arterial PCO2 are located in the ventral area of the medulla oblongata, near the exit of the ninth and tenth cranial nerves. These chemoreceptor neurons are anatomically separate from, but synaptically communicate with, the neurons of the respiratory control center in the medulla.

An increase in arterial PCO2 causes a rise in the H+ concentration of the blood as a result of increased carbonic acid concentrations. The H+ in the blood, however, cannot cross the blood-brain barrier, and thus cannot influence the medullary chemoreceptors. Carbon dioxide in the arterial blood can cross the blood-brain barrier and, through the formation of carbonic acid, can lower the pH of cerebrospinal fluid (fig. 16.30). This



Normal ventilation (Pco2= 40 ± 2)


Chemoreceptor neurons



-Medulla oblongata

Blood Csf Barrier

— Blood-CSF barrier

— Capillary blood

-Cerebrospinal fluid (CSF)

— Blood-CSF barrier

— Capillary blood

Total minute volume (L/min)

■ Figure 16.28 The relationship between total minute volume and arterial PCO2. Notice that these are inversely related: when the total minute volume increases by a factor of 2, the arterial Pco2 decreases by half. The total minute volume measures breathing, and is equal to the amount of air in each breath (the tidal volume) multiplied by the number of breaths per minute. The PCO2 measures the CO2 concentration of arterial blood plasma.

Pco2 And Total Minute Volume

■ Figure 16.29 Chemoreceptor control of breathing. This figure depicts the negative feedback control of ventilation through changes in blood PCO2 and pH. The blood-brain barrier, represented by the orange box, allows CO2 to pass into the cerebrospinal fluid but prevents the passage of H+.

■ Figure 16.30 How blood CO2 affects chemoreceptors in the medulla oblongata. An increase in blood CO2 stimulates breathing indirectly by lowering the pH of blood and cerebrospinal fluid (CSF). This figure illustrates how a rise in blood CO2 increases the H+ concentration (lowers the pH) of CSF and thereby stimulates chemoreceptor neurons in the medulla oblongata.

fall in cerebrospinal fluid pH directly stimulates the chemoreceptors in the medulla when there is a rise in arterial Pco2-

The chemoreceptors in the medulla are ultimately responsible for 70% to 80% of the increased ventilation that occurs in response to a sustained rise in arterial Pœ2. This response, however, takes several minutes. The immediate increase in ventilation that occurs when PCO2 rises is produced by stimulation of the peripheral chemoreceptors.

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  • elisa negassi
    Can carbonic acid pass the blood brain barrier?
    8 years ago
  • leena
    How pco2 penetrate blood brain barrier?
    8 years ago
  • annett schneider
    How blood brain barrirer influences ventilation?
    8 years ago
  • heike
    How is the medulla indirectly affected by co2 levels in blood?
    8 years ago
  • Ute
    How is CO2 detected by the medulla oblongata?
    8 years ago
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    What stimulates the chemoreceptors in the medulla?
    7 years ago
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    How is blood pco2 detected in the human body?
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    How blood CO2 affects chemoreceptors in the medulla oblongata?
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    Are chemoreceptors in medulla obulongata?
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