Muscles involved in quiet expiation:

Apa from the diaphragm and the intercostals, other less impoant muscles also contract on inspiration and assist in elevating the ribs, namely, the levatores costarum muscles and the serratus posterior superior muscles. Quiet expiration occurs passively by the elastic recoil of the pulmonary alveoli and thoracic wall.In deep forced inspiration, a maximum increase in the capacity of the thoracic cavity occurs. Every muscle that can raise the ribs is brought into action, including the scalenus anterior and medius and the sternocleidomastoid.In respiratory distress the action of all the muscles already engaged becomes more violent, and the scapulae are fixed by the trapezius, levator scapulae, and rhomboid muscles, enabling the serratus anterior and pectoralis minor to pull up the ribs. Forced expiraion is brought about by the muscles of the abdominal wall and the latissimus dorsi