Expiration involves
(A) Relaxation of diaphragm and intercostal muscles
(B) Contraction of diaphragm and intercostal muscles
(C) Contraction of diaphragm muscles
(D) Contraction of intercostal muscles
Answers
Answer:
Answer is (A)
Explanation:
Expiration is the phase of ventilation in which air is expelled from the lungs. It is initiated by relaxation of the inspiratory muscles:
Diaphragm – relaxes to return to its resting position, reducing the superior/inferior dimension of the thoracic cavity.
External intercostal muscles – relax to depress the ribs and sternum, reducing the anterior/posterior dimension of the thoracic cavity.
The relaxation of the inspiratory muscles results in a decrease in the volume of the thoracic cavity. The elastic recoil of the previously expanded lung tissue allows them to return to their original size.
Answer:
(A)
Explanation:
When drawing breath (i.e., during inspiration), the external intercostal muscles and diaphragm contract simultaneously. This causes the thorax to expand and inflate the lungs by creating negative pressure inside the thoracic cavity. During expiration, the contraction of these muscles ceases, causing them to relax.
The lungs can contract in a manner similar to a deflating balloon. When the muscles that expand the thorax are relaxed, the lungs contract by their own elastic recoil forces, so that breath is expired. This is what happens to intercoastal muscles whereas During inspiration, the diaphragm contracts and pulls downward while the muscles between the ribs contract and pull upward. During expiration, the diaphragm relaxes, and the volume of the thoracic cavity decreases, while the pressure within it increases. As a result, the lungs contract and air is forced out. Hence option (A) is the correct answer.
Hope you've understood!!