Explain the control of breathing.
Most candidates provided a structured answer based around a sensor / central integration / effector model with appropriate weighting towards the sensor / integration component. Better answers provided an understanding of details of receptor function, roles of the medullary and pontine nuclei and how these are thought to integrate input from sensors. Marks were awarded to PaCO2 ventilation and PaO2 ventilation response when accurate, correctly labelled diagrams or descriptions were provided.
| Sensor | Stimulus | Afferent nerve |
|
Carotid body glomus |
|
Glossopharyngeal |
| Aortic glomus cells - in the aortic arch, subclavian arteries and pulmonary trunk |
|
Aortic nerve (branch of the vagus) |
| Central chemoreceptors |
|
- |
| Mechanoreceptors in bronchial and lung tissue |
|
Vagus |
| 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.