The Mechanism Of Breathing

Question 1

What do the internal and external intercostal muscles do

Answer 1

Internal - contraction leads to expiration

External - contraction leads to inspiration

Question 2

What happens during inspiration

Answer 2

External intercostal muscles contract, internal intercostal muscles relax

Ribs are pulled upwards and outwards-increasing volume of thorax

Diaphragm contract, causing it to flatten - increasing volume of thorax

Increase volume in thorax = reduction of pressure in lungs

Atmospheric pressure is now greater than pulmonary pressure and so air is forced into the lungs

Question 3

What happens during expiration

Answer 3

Internal intercostal muscles contract, external intercostal muscles relax

Ribs are pulled downwards and inwards- decreasing volume of thorax

Diaphragm relaxes, causing it to dome - decreasing volume of thorax

Decrease volume in thorax = increases pressure in lungs

Pulmonary pressure is now greater than atmosphere and so air is forced out of the lungs