Steps of Inspiration
Nerve Impulses travel on phrenic nerves to muscle fibers in the diaphragm, contracting them.
As the dome-shaped diaphragm moves downward, the thoracic cavity expands.
At the same time, the external intercostal muscles may contract raising the ribs and expanding the thoracic cavity further
The intra-alveolar pressure decreases.
Atmospheric pressure, greater on the outside, forces air into the respiratory tract through the air passages.
The lungs fill with air.