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i)During inhalation.
Energy provided by muscles causes air to enter into the lungs. The diaphragm (dome-shaped muscle) is the primary inspiratory muscle. It contracts and the dome is pulled caudally during inspiration whereby the thoracic cavity is enlarged. The external intercostals muscles (which join ribs) also contract during inspiration. The help in moving the ribs rostrally and outwards.
ii)During exhalation.
Much of the energy causing air to leave the lungs is provided by the elastic force stored in the stretched lung and thorax. Thus in most animals at rest, inhalation is an active process
whereas exhalation is passive. The abdominal muscles and internal intercostals muscles are the expiratory muscles. Contraction of abdominal muscles increases abdominal pressure, which forces the relaxed diaphragm forward and reduces the size of the thorax. Contraction of internal intercostals muscles decreases the size of the thorax by moving the ribs caudally and ventrally.
sharon kalunda answered the question on February 25, 2019 at 13:45