6.7 The mechanism of breathing.

Question 1

What are the main muscles involved in breathing?

Answer 1

DIAPHRAGM: a sheet of muscle separating the thorax and the abdomen.
INTERCOSTAL MUSCLES: lie between the ribs, split into two sets;
- internal intercostal muscles: contract for expiration
- external intercostal muscles: contract for inspiration.

Question 2

Describe the process of inspiration.

Answer 2

Inspiration is an active process.

1) External IMs contract, internal IMs relax
2) Ribs are pulled upwards and outwards, increasing the volume of the thorax.
3) Diaphragm contracts, flattening itself and increasing the volume of the thorax
4) Increased volume of the thorax, decreasing pressure in the lungs so air is forced in.

Question 3

Describe the process of expiration.

Answer 3

expiration is a largely passive process.

1) Internal IMs contract, external IMs relax.
2) Ribs move down and inwards, decreasing the thorax volume
3) Diaphragm relaxes so is pushed up by compressed abdomen
4) decreased thorax volume increases the pressure in lungs so air is forced out.