The mechanism of breathing

• External intercostal muscles contract, whilst the internal intercostal muscles relax
• Ribs are pulled upwards and outwards, increasing the volume of the thorax
• Diaphragm muscles contract, causing it to flatten, further increases volume of the thorax.
• Increased volume of the thorax causes reduction of pressure in lungs
• Atmospheric pressure is now greater than pulmonary pressure and so air rushes into the lungs

THINK OF A DIFFUSION GRADIENT

• Internal intercostal muslces contract, whilst the external intercostal muslces relax
• Ribs move downwards and inwards, decreasing he volume of the thorax
• The diaphragm muscle relax, further decreasing the volume of the thorax
• Decreased volume of the thorax increases the pressure in the lungs
• The pulmonary pressure is now greater than atmospheric pressure and so air is forcced out of the lungs.

THINK OF DIFFUSION GRADIENT