The mechanism of breathing: role of the diaphragm and the antagonistic interaction between external and internal intercostal muscles in producing pressure changes in the thoracic cavity
Breathing works by muscles changing the size of your chest cavity. A bigger cavity lowers air pressure inside, so air rushes in. A smaller cavity raises pressure, pushing air out.
Formula
P₁V₁ = P₂V₂ (Boyle's Law: pressure and volume are inversely proportional at constant temperature)
Real World
Anaesthetists rely on precise knowledge of thoracic pressure changes when using mechanical ventilators in surgery — machines that artificially replicate the diaphragm and intercostal muscle actions described here.
Exam Focus
State the muscle action (contracts/relaxes), then the volume change, then the pressure change, then airflow direction — mark schemes reward this logical sequence.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
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