Answer
In quiet inspiration, the diaphragm contracts and the ribs are lifted by the contraction of the external intercostal muscles. This increases the volume of the thoracic cavity and of the lungs ; intrathoracic pressure falls and abdominal pressure rises.
Quiet expiration is passive. The thoracic volume is decreased as the ribs fall and the lungs recoil The intrathoracic pressure increases and the abdominal pressure falls .--to a lesser degree.
Work Step by Step
In forced inspiration thoracic volume also rises, and intrapulmonary pressure falls. In the abdomen volume decreases and pressure also falls
In forced expiration thoracic pressure increases, abdominal volume decreases and abdominal pressure increases
