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The dome-shaped muscle below the lungs that is the body's primary breathing muscle, driving inhalation.
Medically reviewed & updated
The diaphragm is a large, dome-shaped sheet of muscle that separates the chest cavity from the abdomen. It is the body's primary muscle of respiration, doing most of the work of every quiet breath. When it contracts and flattens, it draws air into the lungs.
The diaphragm forms the floor of the thoracic cavity and the roof of the abdominal cavity. Its muscle fibers arise around the lower margin of the rib cage, the back of the sternum, and the upper lumbar vertebrae (via tendon-like bands called crura), and they converge on a strong central tendon at the top of the dome. Three major openings allow important structures to pass between the chest and abdomen: the aortic hiatus (aorta), the esophageal hiatus (esophagus), and the caval opening (inferior vena cava). The diaphragm receives its motor nerve supply from the phrenic nerve, which arises from spinal nerves C3, C4, and C5, a fact captured by the clinical memory aid "C3, 4, 5 keep the diaphragm alive."
When the diaphragm contracts, the dome flattens and descends, enlarging the chest cavity and lowering the pressure inside it. This pressure drop pulls air into the lungs (inhalation). When it relaxes, it springs back upward, the chest cavity shrinks, and air is pushed out (exhalation). The diaphragm works with the intercostal muscles between the ribs to power breathing. It also assists with non-respiratory efforts that raise abdominal pressure, such as coughing, sneezing, vomiting, and bearing down during childbirth or defecation.
Because the phrenic nerve originates high in the neck, injury to the cervical spinal cord or to the phrenic nerve can paralyze part or all of the diaphragm and impair breathing. A hiatal hernia occurs when part of the stomach pushes up through the esophageal opening, contributing to acid reflux. A congenital diaphragmatic hernia is a birth defect in which abdominal organs move into the chest and crowd the developing lungs. Irritation of the diaphragm can cause referred pain to the shoulder, and involuntary diaphragm spasms produce hiccups.
This page is educational and not a substitute for professional medical advice.