Final answer:
The ability to take a deep breath is enabled by the contraction of the diaphragm and external intercostal muscles, which expands the thoracic cavity, allowing for lung expansion and air intake. Exhalation is a passive process where these muscles relax and the elastic recoil of the lungs expels the air.
Step-by-step explanation:
The ability to take a deep breath primarily involves the contraction of the diaphragm and external intercostal muscles. When taking a deep breath, also known as diaphragmatic breathing, the diaphragm contracts forcefully, moving downwards to increase the volume of the thoracic cavity, allowing the lungs to expand and fill with air. This expansion causes the pressure inside the lungs to drop below atmospheric pressure, causing air to flow in. Additionally, the external intercostals contract to expand the chest wall outward, which further assists in lowering pressure within the thoracic cavity, drawing air into the lungs. As you exhale, the diaphragm and the intercostal muscles relax, and the elastic recoil of the lungs helps to push air out in a passive process.