Question

Copy and complete the table, which shows what happens in the thorax during ventilation of the lungs. Two boxes have been completed for you.

	Action during inhalation	Action during exhalation
external intercostal muscles	Contract
Internal intercostal muscles
ribs		move down and in
diaphragm
volume of thorax
pressure in thorax
volume of air in lungs

Answer 1

	Action during inhalation	Action during exhalation
external intercostal muscles	Contract Relax
Internal intercostal muscles	Relax Contract
ribs	Expand (move up and out)	move down and in
diaphragm	Contract Relax
volume of thorax	Increases Decreases
pressure in thorax	Decreases Increases
volume of air in lungs Increases Lungs are involved in pulmonary respiration in terrestrial vertebrates. The lungs are encased in a protective ribcage which is made up of ribs and sternum. Intercostal muscles are attached with the ribs which are of 3 types internal, external and innermost. They help in the breathing process by moving the chest wall. The diaphragm is situated below the lungs in the thoracic cavity it contracts and relax as per the movement of the lungs to increase and decrease the volume of the chest cavity. While inhaling the external muscles contract and internal intercostal muscles relax due to which the ribs move up and out which increases the volume in the chest cavity and the diaphragm contracts and takes a dome shape. due to increase in the chase cavity the volume in the lungs in increases due to which the pressure decrease and the air from the atmosphere enters the lungs. during exhalation the opposite process takes place ie the external intercostal muscles relax and inner intercostal muscles contract. The ribs move down and in the diaphragm relaxes and goes back to its original shape due to which volume in the chest cavity decreases and the pressure in the lungs increases due to which the air from the lungs moves out to the atmosphere.