Control of Breathing

  • The carotid body, aortic body and medulla contain chemoreceptors, which detect changes in CO2 level (H+ ion concentration) of the blood. 
  • These receptor cells send nervous impulses to the respiratory centre in the brain. 

  • The higher the CO2 concentration (and therefore [H+]) the more frequently they send impulses to the respiratory centre 

  • The respiratory centre in the brain contains two sections an inspiratory centre and an expiratory centre. 

  • Nerves impulses are sent from the inspiratory centre of the respiratory centre in the medulla to the diaphragm and intercostals. 

  • These impulses (from respiratory centre) cause muscle to contract.
  • Contraction of intercostal muscles and contraction of diaphragm causes ribs to move up and out and the diaphragm to move down which increases volume of thorax/lungs thereby decreasing pressure (causing inspiration).
  • Stretch receptors in the intercostal muscles are stimulated by increase in size of thorax/lungs.
  • These receptors send impulses to the expiratory centre which inhibits the inspiratory centre therefore inspiratory impulses are inhibited so contraction of the diaphragm and intercostals ceases and elastic recoil of the lung tissue causes expiration.

Summary Diagram of the control of breathing