#84 Ventilation, role of intercostal muscles and diaphragm

There are 2 sets of muscles which help you to breath:

- intercostal: between the ribs

- diaphragm: a large sheet of muscle and elastic tissue, underneath the lungs and heart. 

Figure below shows the relationship between intercostal muscles, diaphragm and ribcage to achieve ventilation of the lungs.

Two set of intercostal muscles are attached to the ribes. They are antogonistic.

1. Breathing in (inhaling)

• The external intercostal muscles contract, they move the ribcage upward and outward ---> ↑ volume of the thorax.
• The diaphragm muscles contracts ---> diaphragm moves down 
• ↑  volume of the thorax
• ↓ air pressure in the thoracic cavity
•  air rush into the lungs through the mouth or nose.

2. Breathing out (exhaling) 

The opposite happens:

• The internal intercostal muscles contract
• The diaphragm muscles relax ---> diaphragm moves up 
• ↓  volume of the thorax
• ↑ air pressure in the thoracic cavity
•  air rush out of the lungs.

Features	Inspiration	Expiration
Intercostal muscles	external muscles contract	internal muscles contract
Ribcage moving	upward outward	downward
Diaphragm muscles	contract	relax
Diaphragm	move ↓	move ↑
Thorax volume	↑	↓
Air pressure in thorax cavity	↓ lower than air pressure outside	↑ higher than air pressure outside
air rushes	into the lungs	out of the lungs