Diaphragm

About the Diaphragm

The diaphragm is the primary muscle of inspiration, a dome shaped sheet separating the thoracic and abdominal cavities. It originates from the xiphoid process, lower six ribs, and lumbar vertebrae via crura, inserting into the central tendon. The right hemidiaphragm is slightly higher due to the liver. The phrenic nerves, arising from the C3, C4, and C5 spinal roots and remembered by the phrase C3, 4, 5 keeps the diaphragm alive, supply its motor innervation, explaining why high cervical spinal cord injuries affect breathing while lower injuries do not. During inspiration, the diaphragm contracts and flattens, increasing thoracic volume and creating negative pressure drawing air in. It accounts for 70 to 80 percent of quiet breathing. During expiration, it relaxes and domes upward. The diaphragm has three hiatuses: T8 caval for the inferior vena cava, T10 esophageal hiatus, T12 aortic hiatus. Hiatal hernias occur through the esophageal hiatus. Hiccups are diaphragmatic spasms.