Questions on breathing

Which two sets of muscles bring about the increase in volume of the thorax at the start of inhalation, and how do they do so?

Which set of muscles is most important in your own breathing at rest, and what happens to the relative importance after exercise?

It is essential that the thorax is airtight. Explain why this is so and why the lungs are in two, separate, airtight compartments.

What actually causes air to flow into the lungs during inhalation?

What is the principal driving force for exhalation at rest?

Exhalation can be an active or forced process (although it is not normally so). Try blowing out as much air as possible from your own lungs to find out which sets of muscles are involved, and then explain what happens.

We have conscious control over the muscles in our arms and in our legs but the muscles of the intestine are controlled unconsciously. What, therefore, is rather unusual about the muscles associated with breathing?