Muscles of the Thorax
The thorax cage is more or less entirely covered in muscles. Many, such as the pectoral muscles running from the anterior thoracic wall to the humerus in the upper limb and the abdominal muscles running from the lower ribs down to the pelvis, can play a role in ventilation. The intercostal muscles of the thoracic wall are located beneath the postural muscle layer.
Movements of the Thoracic Wall:
Intrathoracic pressure and the volume associated with inspiration and expiration is related to movements of both the thoracic wall and the diaphragm. In fact, the contraction of the diaphragm leads to an increase in the vertical dimension of the thorax.
Commonly Described Movements:
Pump handle movement: The anterior-posterior diameter of the thorax increases when the anterior region of the rib cage and sternum rise and move outwards. This rise occurs as a result of the upper ribs rotating at the costovertebral joints.
Bucket handle movement: The transverse dimension of the thorax increases when there is an outward movement of the lateral regions of the middle ribs.