Answer:
In quiet breathing inspiration involves muscular contractions and expiration is passive.
Explanation:
Respiration process involves two different stages, inspiration - inhalation- and expiration - exhalation-.
During inspiration, the diaphragm <u>contracts</u> and goes down, while intercostal muscles also <u>contract</u> and go up. These actions enhance the size of the thoracic box and <u>reduce internal pressure</u>. As a result, air flows in and fills the lungs.
During expiration, the <u>diaphragm relaxes</u> and the volume of the thoracic box diminishes, which causes the <u>pressure inside to increase</u>. In consequence, the lungs contract and the air is expulsed outside.
