Explain the control of breathing.
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.
Discussion
| 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 |
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