In respiratory medicine/physiology, ventilation is driven by three functional muscle groups—accessory chest-wall muscles (recruited only during forced respiration), the intercostal muscles (external, internal, and subcostal layers, with distinct fiber orientations governing inspiration versus forced expiration), and the diaphragm, the primary muscle of quiet inspiration, which flattens on contraction to expand thoracic volume. The diaphragm's function depends on innervation by the phrenic nerve (cervical roots C3-C5), and its structural openings for the esophagus, aorta, and inferior vena cava represent a general principle of diaphragmatic anatomy: these apertures are also potential sites of herniation.
In respiratory medicine/physiology, ventilation is driven by three functional muscle groups—accessory chest-wall muscles (recruited only during forced respiration), the intercostal muscles (external,…