Explain the control of breathing.

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College Answer

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 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



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