Breathing
Science: KS3, topic 1.6.16
Breathing
Inspiration (breathing in) and expiration (breathing out) involve many parts of the thorax moving in the following steps:
Inspiration
- The diaphragm contracts and becomes flattened.
- The internal intercostal muscles relax and the external intercostal muscles contract, moving the ribcage up and out.
- The thorax volume increases, forcing air into the lungs because of decreased internal pressure.
Expiration
- The diaphragm relaxes and becomes dome-shaped.
- The internal intercostal muscles contract and the external intercostal muscles relax, moving the ribcage downwards and in.
- The thorax volume decreases, increasing internal pressure.
- Air is forced out of the lungs.
Test yourself on Breathing
Expiration
Inspiration
What happens in the thorax during inspiration?
What part of the body changes in volume during breathing?
Name the two properties of the thorax that change during breathing.