Fig. 1
From: Ultrasonographic assessment of parasternal intercostal muscles during mechanical ventilation
Intercostal muscles anatomy. A schematic picture of anatomy and function of internal and external intercostal muscles. Panel A: the figure represents the anatomical distribution of intercostal muscles. Panel B: the figure represents the schematic functional activity of intercostal muscles. In particular, the external intercostal connects the ribs in such a way that contraction of the muscles lift the ribs and the rib cage allowing to expand the anterior–posterior dimension of the chest wall. On the other hand, the contraction of the internal intercostal (oriented opposite to the external) determines the opposite effect such as lowering of the ribs and reducing the anterior–posterior dimension