ventilation

Question 1

inhalation

Answer 1

diaphragm contracts, intercostal muscles contract; moving the ribcage up and out:
volume of thorax increased
air pressure in thorax falls / decreases

air pressure in thorax is less than atmospheric pressure causing air to move into the lungs

Question 2

exhalation

Answer 2

diaphragm relaxes, intercostal muscles relax; moving ribcage down and in:
volume of thorax decreases
air pressure in thorax rises / increases

air pressure in thorax is more than atmospheric pressure cause air to move out of the lungs