diaphragm
Meaning of diaphragm: Breathing runs automatically because this muscle answers a signal from the phrenic nerves, which arise high in the neck.
Definition of diaphragm
The diaphragm is the broad, dome-shaped sheet of muscle that separates the chest from the abdomen and performs most of the work of breathing. When it contracts it flattens and moves downward, enlarging the chest so that air is drawn into the lungs; when it relaxes it rises again and air leaves. The phrenic nerves supply it.
What passes through the diaphragm?
The muscle is a partition, not a seal. Three large structures cross it through separate openings, each at a different level, along with several smaller nerves and vessels. The openings matter clinically because they are natural weak points.
| Opening | What passes through | Note |
|---|---|---|
| Caval opening | Inferior vena cava | Sits in the tendinous center, so it is held open |
| Esophageal hiatus | Esophagus and vagus nerves | Muscle fibers around it help keep stomach contents down |
| Aortic hiatus | Aorta, thoracic duct | Passes behind the muscle rather than through its fibers |
What does it do besides breathing?
Contracting the diaphragm against a closed airway raises pressure inside the abdomen, and that pressure is used for coughing, sneezing, vomiting, emptying the bowel and pushing during childbirth. The muscle fibers wrapped around the esophageal opening act as an external sphincter that resists reflux of stomach contents. The diaphragm also keeps working during sleep and under anesthesia without conscious control, driven by respiratory centers in the brainstem that adjust the rate and depth of breathing to the level of carbon dioxide in the blood.
What goes wrong with it?
Injury to a phrenic nerve, from surgery, a tumor or a neck injury, paralyzes that half of the muscle. The affected side sits higher than normal and no longer descends, which shows on imaging and causes breathlessness that is worse lying flat. Because the phrenic nerves arise from nerve roots high in the neck, a spinal cord injury above that level removes the drive to breathe altogether. A hiatal hernia is a different problem: part of the stomach slides up through the esophageal opening rather than the muscle failing. Hiccups are involuntary spasms of the same muscle. A rarer congenital form leaves a gap in the sheet before birth, allowing abdominal organs into the chest. Confusingly, the word also names an unrelated barrier contraceptive, a flexible dome placed over the cervix.
Used in a sentence
The imaging study evaluated the position and movement of the diaphragm during breathing.
Good to know
A hiatal hernia involves stomach contents pushing up through the diaphragm's normal opening for the esophagus, which is a different problem from weakness or paralysis affecting the muscle's ability to contract.
Word origin
Where “diaphragm” comes from
Formed from Greek dia-, meaning across, and phragma, meaning a fence or partition, describing the muscle's role in separating the chest from the abdomen.