Describe how the diaphragm and intercostal muscles bring about inhalation (breathing in). [4]
- (external) intercostal muscles contract; accept ribs move up and out(1)
- diaphragm (muscle) contracts; accept flattens / moves down(1)
- volume of the thorax / chest cavity increases; accept volume of lungs increases(1)
- pressure inside the thorax / lungs decreases (below atmospheric pressure) so air moves in; reject 'air is sucked in so pressure decreases' (wrong order)(1)
- Answer: Intercostals contract (ribs up and out), diaphragm contracts and flattens, thorax volume rises, pressure falls, air drawn in.
- Examiner tip: Pressure and volume must be in the right order: volume increases FIRST, which lowers the pressure.