Nervous control of heart rate and breathing – medulla, baroreceptors, chemoreceptors and the nervous system
BiologyHuman & Animal PhysiologyAges 16–17
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Sign in to playThe medulla receives impulses from baroreceptors in the carotid sinus and aortic arch and from chemoreceptors in the medulla and in the carotid and aortic bodies, then sends impulses along the sympathetic and vagus nerves to the SA node and along the phrenic nerve to the diaphragm. Change exercise intensity, inspired CO₂, altitude and posture, cut the vagus nerve or all the nerves to the heart, hold your breath, over-breathe or get a fright, and watch heart rate, blood pressure, breathing rate, PCO₂ and pH while you record a results table. A nervous system screen maps the CNS, the somatic nerves and the sympathetic and parasympathetic systems, and compares reflexes with voluntary responses.
Lesson: Nervous coordination – control of heart rate and breathing, reflexes and voluntary responses
What it shows
Heart rate and breathing are adjusted all the time without conscious thought. The medulla oblongata in the brain stem contains a cardiovascular centre and a respiratory centre. Baroreceptors in the carotid sinus and aortic arch detect blood pressure, and chemoreceptors detect carbon dioxide, pH and oxygen. The cardiovascular centre speeds the SA node through sympathetic nerves and slows it through the vagus nerve, while the respiratory centre drives the diaphragm and intercostal muscles. Both are examples of negative feedback, part of the autonomic nervous system that this simulation also maps.
How to use
On Heart and breathing control, drag Exercise, Inspired CO₂ or Altitude, wait for the graphs to level off (choose 4 × faster) and press Record values. Press Stand up, choose Nerves to the heart, press Fright, or press Hold breath and watch PCO₂ rise. On Nervous system map, choose a Response and press Stimulate; use the Show buttons and tap body parts.
Parameters you can change
- Screen Heart and breathing control, Nervous system map
- Exercise intensity 0–100 %
- CO₂ in inspired air 0–6 %
- Altitude 0–5500 m
- Posture Lying down, Standing
- Nerves to the heart Intact, Vagus nerve cut, All nerves to the heart cut
- Speed Real time, 4 × faster
- Response Withdrawal reflex from a hot object, Pupil reflex in bright light, Voluntary response: catching a ball
Questions to explore
- Why does heart rate rise to about 100 beats per minute when the vagus nerve is cut?
- How do chemoreceptors and the medulla bring blood CO₂ back to normal during exercise?
- Why is it dangerous to over-breathe before swimming underwater?
