Inspiration is an active process that uses energy.Contraction of the inspiratory muscles expands the chest wall, lowering the pressures in the thoracic cavity.1. The internal intercostal muscles relax. The external intercostal muscles contract. The ribs are pulled upwards and outwards.2. The diaphragm contracts. Causing it to flatten.3. The volume of the thorax increases as a result of the movement of the ribs and diaphragm.4. The pressure in the thorax decreases because of the increased volume.5. Atmospheric pressure is greater than the pressure in the lungs so air is forced into the lungs.The elastic tissue between the alveoli stretch as the alveoli are filled with air.The diaphragm is a sheet of internal skeletal muscle in humans and other mammals that extends across the bottom of the thoracic cavity that separates the thoracic cavity, containing the heart and lungs, from the abdominal cavity.It is usually domed or curved upwards when relaxed