4. In quiet breathing, a. None of the options is correct b. Inspiration and expiration are both passive processes c. Inspiration is passive and expiration involves muscular contractions d. Inspiration involves muscular contractions and expiration is passive

d. Inspiration involves muscular contractions and expiration is passive

Explanation:

Breathing is the process of taking air in and out of the body or more specifically taking oxygen in and moving carbon dioxide out of the body. Our respiration rate is regulated by medulla in brain and alter according to our activities.

Quiet breathing is slow, relaxed breathing that lowers the blood pressure, slows the heart rate beat and calms the mind. It is done while sitting or maintaining a proper posture that require less energy and opposite to deep breathing that done during energetic activities like running.

Diaphragm is the main muscle movement during quiet breathing, which must contract to carry out it because its contraction draw the air to alveoli. So inspiration involves the contraction of muscles but the expiration is passive in quiet breathing. The reason is that due to the relaxed elastic muscles, the lungs and chest wall regain their resting volume according to the functional residual capacity.