| The diaphragm | - Sheet of muscle that separates the thorax from the abdomen |
| The intercostal muscles | - Lie between the ribs
- Two set of intercostal muscle: Internal + external |
| Internal intercostal muscles | - Contraction leads to expiration |
| External intercostal muscles | - Contraction leads to inspiration |
| Ventilation | - Breathing in and out |
| Thoracic cavity | - Space where the lungs are |
| Lung pressure | - Air will always move from a region of higher pressure to a region of lower pressure
- Down pressure gradient
- Air moves down the trachea into the lungs |
| Inspiration | - The external intercostal + diaphragm muscles contract
- The ribcage moves up + out
- Diaphragm flattens, increasing volume of thoracic cavity
- Pressure decreases
- Active process, requires energy |
| Expiration | - The external intercostal + diaphragm muscles relax
- The ribcage moves down + in
- Diaphragm curves again, decreasing volume of thoracic cavity
- Pressure increases
- Air forced down pressure gradient out of lungs
- Passive process, no energy needed |
| Forced expiration | e.g. blowing candles on cake
- External intercostal muscles relax
- Internal intercostal muscles contract
- Pulling ribcage further down + in
- During this, movement of the two set of i.ms is called antagonistic (opposite) |
