Aperture
The diaphragm is a thin, dome-shaped muscle that separates the chest and abdominal cavities. This is the main respiratory muscle: it accounts for up to 70% of the volume of a quiet inhalation. During contraction, the dome flattens, the volume of the chest increases, and air rushes into the lungs.
Building
The diaphragm consists of muscle and tendon parts:
The tendon center is a dense fibrous plate at the top of the dome on which the heart lies (through the pericardium). The center does not contract, but serves as a fixation point.
Muscular part has three sections at the point of origin:
- Sternal part - from the xiphoid process
- Rib part - from the inner surface of the lower six ribs
- Lumbar part - from the bodies of the lumbar vertebrae (right and left legs)
The right leg is longer and thicker than the left: it starts from L1–L3, while the left leg starts only from L1–L2.
Three main holes
Vital structures pass through the diaphragm:
| Hole | Level | What's going on |
|---|---|---|
| Aortic | Th12 | Aorta, thoracic lymphatic duct |
| Esophageal | Th10 | Esophagus, vagus nerves |
| Opening of the inferior vena cava | Th8 | Inferior vena cava |
Mnemonic for remembering levels: 8–10–12 (vein - esophagus - aorta, from bottom to top along the vertebrae).
The aortic opening is located behind the diaphragm (between the legs), so when the muscle contracts, the aorta is not compressed. The esophageal opening is surrounded by muscle fibers that act as a sphincter, preventing the reflux of gastric contents into the esophagus.
Innervation
The diaphragm is innervated by the phrenic nerve (n. phrenicus), which is formed from the C3–C5 roots of the cervical plexus. This explains the paradoxical fact: the main muscle of the abdomen and chest is controlled by a nerve from the neck. Spinal cord injury above the C3 level results in paralysis of the diaphragm and the inability to breathe independently.
Doctors remember this with the rule: “C3, 4, 5 keeps the diaphragm alive”.
Pathologies
Diaphragmatic hernia is a protrusion of the abdominal organs into the chest cavity through a defect in the diaphragm. The most common form is a hiatal hernia, in which the upper part of the stomach is displaced into the chest cavity. Manifested by heartburn, belching and chest pain.
Hiccups is an involuntary convulsive contraction of the diaphragm with a sharp closure of the glottis. Usually harmless, persistent hiccups (more than 48 hours) may indicate irritation of the phrenic nerve by swelling or inflammation.
Studying the diaphragm in Humio's 3D atlas helps you understand its spatial relationship to surrounding structures—rotate the model to see the legs, openings, and dome in a way not possible in flat illustrations.