EVERYDAY SCIENCE

Detailed explanation-1: -Inspiration :-during inspiration, external intercostal muscles play an important role . These muscles are present between ribs. The contraction of these muscles lift ribs and sternum up and outward causing an increase in the volume of the thoracic cavity in the dorso-ventral axis, i.e., backward-forward direction.

Detailed explanation-2: -As the rib cage and sternum (breast bone) move upward and outward, the thoracic volume would increase and with this the pulmonary volume would also increase. This would create a negative pressure gradient in lungs, which would mean pressure in lungs less than the atmosphere. Thus, inspiration would happen.

Detailed explanation-3: -The intrapulmonary pressure also known as intrapleural pressure does not increase but decreases during the inspiration process. The average intrapulmonary pressure of a human lung is 759 mmHg or lower.