How exactly does the chest wall work?

Inspiration can mean different things to different people. But for the astute medical student, the first thought should be about human respiration. It involves, among other things, a combination of muscular contraction and movement of the rib cage, such that the dimensions of the thorax are increased, the principal driving force behind this being the diaphragm. Contraction of the diaphragm draws the floor of the thorax down, resulting, in effect, in an increase in the superior-inferior dimension of the cavity.

At the same time, the upper ribs (comprising the second to the seventh) move forwards and upwards, like the action of a pump handle, expanding the anteroposterior dimension of the cavity (fig 1). The lower ribs (eighth to the 10th) swing in an upward and lateral direction similar to the movement of bucket handles. This considerably increases the transverse dimensions of the thorax (fig 2).