inspiration and expiration

• inspiration:

  diaphragm contracts and becomes flattened

  internal intercostal muscles contract and external intercostal muscles relax moving the ribcage up and out

  the thorax volume increases forcing the air into the lungs because of decreased internal pressure
• expiration:

  diaphragm relaxes and becomes dome shaped

  internal intercostal muscles relax and external intercostal muscles relax moving the ribcage downwards and in

  the thorax volume decreases increasing internal pressure

  air is forced out of the lungs