Question 1

Explain the control of breathing.

[Click here to toggle visibility of the answers]

College Answer

This question was generally well done. It was expected answers would include discussion of
the three core elements of sensors, a central controller and effectors. Central control involves 
three main groups of neurones in the brainstem with some cortical voluntary control also 
possible. More in depth answers included graphs of the ventilatory response to oxygen and 
carbon dioxide tensions.


This question is essentially identical to Question 13 from the second paper of 2015, except that this time the college also expected graphs to illustrate the ventilatory response to oxygen and carbon dioxide. These graphs can be found in any decent physiology textbook, and they usually look like this:

ventilatory responses to hypercapnia and hypoxia

Sensor Organs involved in the Control of Respiratory Function
Sensor Stimulus Afferent nerve

Carotid body glomus
(Type I cells) - sited at the bifurcation of the common carotid

  • PaO2
  • PaCO2
  • pH
  • Temperature
  • Glucose (hypoglycaemia)
Aortic glomus cells - in the aortic arch, subclavian arteries and pulmonary trunk
  • PaO2
  • Changes in O2 delivery (anaemia, carboxyhaemoglobin, hypotension)
  • PaCO2
Aortic nerve
(branch of the vagus)
Central chemoreceptors
  • pH
Mechanoreceptors in bronchial and lung tissue
  • Inflation and deflation (i.e. Hering-Breuer reflex)
Respiratory Control Centres
Controller Role Efferents and effectors
Nucleus retroambigualis Expiratory function

Upper motor neuron axons to contralateral expiratory muscles

Nucleus paraambigualis Inspiratory function

Upper motor neuron axons to contralateral inspiratory muscles

Nucleus ambiguous Airway dilator function

Vagus nerve: to (larynx, pharynx and muscularis uvulae)

Glossopharyngeus muscle to stylopharyngeus muscle

Pre-Bötzinger complex Respiratory pacemaker ("central pattern generator") Interneurons connecting to other respiratory control regions
Bötzinger complex Expiratory function

Inhibitory interneurons to phrenic motor neurons and other respiratory control regions

Pontine respiratory group

Integrates descending control of respiration from the CNS

Interneurons connecting to other respiratory control regions
Cerebral cortex Volitional and behavioural  respiratory control Pontine respiratory group


Wolff, Christopher B. "The physiological control of respiration." Molecular aspects of medicine 13.6 (1992): 445-567.

Henderson, V. E., and E. Horne Craigie. "On the respiratory centre." American Journal of Physiology-Legacy Content115.3 (1936): 520-529.

Remmers, John E. "A century of control of breathing." American journal of respiratory and critical care medicine172.1 (2005): 6-11.

 Richter, D. W., F. Heyde, and M. Gabriel. "Intracellular recordings from different types of medullary respiratory neurons of the cat." Journal of neurophysiology 38.5 (1975): 1162-1171.

López-Barneo, J., et al. "Carotid body oxygen sensing." European Respiratory Journal 32.5 (2008): 1386-1398.

Prabhakar, Nanduri R., and Ying-Jie Peng. "Peripheral chemoreceptors in health and disease." Journal of Applied Physiology 96.1 (2004): 359-366.

Atanasova, Dimitrinka Y., Michail E. Iliev, and Nikolai E. Lazarov. "Morphology of the rat carotid body." Biomedical Reviews 22 (2011): 41-55.

Ortega‐Sáenz, Patricia, et al. "Cellular properties and chemosensory responses of the human carotid body." The Journal of physiology 591.24 (2013): 6157-6173.

López-Barneo, José. "Oxygen sensing and stem cell activation in the hypoxic carotid body." Cell and tissue research 372.2 (2018): 417-425.

Nattie, Eugene. "Why do we have both peripheral and central chemoreceptors?." Journal of Applied Physiology 100.1 (2006): 9-10.

Smith, Curtis A., et al. "Response time and sensitivity of the ventilatory response to CO2 in unanesthetized intact dogs: central vs. peripheral chemoreceptors." Journal of Applied Physiology 100.1 (2006): 13-19.

Lahiri, S., et al. "Relative responses of aortic body and carotid body chemoreceptors to carboxyhemoglobinemia." Journal of Applied Physiology 50.3 (1981): 580-586.

Lahiri, S., et al. "Relative responses of aortic body and carotid body chemoreceptors to hypotension." Journal of Applied Physiology 48.5 (1980): 781-788.

Prabhakar, Nanduri R. "O2 and CO2 detection by the carotid and aortic bodies." Chemosensory Transduction. Academic Press, 2016. 321-338.

Coleridge, Hazel, J. C. G. Coleridge, and A. Howe. "A search for pulmonary arterial chemoreceptors in the cat, with a comparison of the blood supply of the aortic bodies in the new‐born and adult animal." The Journal of physiology 191.2 (1967): 353-374.

Honda, Yoshiuki. "Respiratory and circulatory activities in carotid body-resected humans." Journal of Applied Physiology 73.1 (1992): 1-8.

Nattie, Eugene, and Aihua Li. "Central chemoreceptors: locations and functions.Comprehensive Physiology 2.1 (2011): 221-254.

Li, Aihua, Shawn Zhou, and Eugene Nattie. "Simultaneous inhibition of caudal medullary raphe and retrotrapezoid nucleus decreases breathing and the CO2 response in conscious rats.The Journal of physiology 577.1 (2006): 307-318.

Phillipson, ELIOT A., James Duffin, and Joel D. Cooper. "Critical dependence of respiratory rhythmicity on metabolic CO2 load." Journal of Applied Physiology 50.1 (1981): 45-54.

Wang, Wengang, Stefania Risso Bradley, and George B. Richerson. "Quantification of the response of rat medullary raphe neurones to independent changes in pHo and PCO2." The Journal of Physiology 540.3 (2002): 951-970.

Ullmann, Elisabeth. "The two original papers by Hering and Breuer submitted by Hering to the KK Akademie der Wissenschaften zu Wien in 1868." Ciba Foundation Symposium‐Breathing: Hering‐Breuer Centenary Symposium. Chichester, UK: John Wiley & Sons, Ltd., 1970

Tryfon, S., et al. "Hering-Breuer reflex in normal adults and in patients with chronic obstructive pulmonary disease and interstitial fibrosis." Respiration 68.2 (2001): 140-144.