Describe the mechanism of breathing in human beings.

(N/A) $1$. Breathing involves two main phases: inhalation and exhalation.
$2$. During inhalation, the diaphragm and external intercostal muscles contract, causing the rib cage to move upward and outward, which increases the thoracic cavity volume.
$3$. This increase in volume leads to a decrease in pressure within the lungs compared to atmospheric pressure, causing air to rush in.
$4$. During exhalation, the diaphragm and intercostal muscles relax, the thoracic cavity volume decreases, and pressure inside the lungs increases, forcing air out.