Diaphragm
The diaphragm is a dome-shaped muscle that separates the thoracic and abdominal cavities. It is the primary muscle of respiration, responsible for approximately 75% of the work of breathing.
Origin, Insertion, Action, Innervation
OOrigin
Sternal part: Xiphoid process. Costal part: Inner surfaces of lower 6 ribs. Lumbar part: Upper lumbar vertebrae via crura (right crus L1-L3, left crus L1-L2).
IInsertion
Central tendon (a flat aponeurosis in the center of the muscle)
AAction
- • Primary muscle of inspiration (contraction flattens the dome)
- • Increases thoracic volume, decreases intrathoracic pressure
- • Assists with abdominal straining (defecation, urination, childbirth)
- • Assists with vomiting and coughing
NInnervation
Phrenic nerve (C3, C4, C5)
Blood Supply
Phrenic arteries, musculophrenic artery, lower intercostal arteries
Clinical Relevance
Phrenic nerve paralysis (e.g., from neck surgery or trauma) causes hemidiaphragm elevation and dyspnea. Hiatal hernia occurs when abdominal contents herniate through the esophageal hiatus. The diaphragm has three major openings: aortic (T12), esophageal (T10), and caval (T8).
Palpation
Cannot be directly palpated. Its function can be assessed by observing abdominal movement during breathing or by fluoroscopy.
Study Tips
- ✓C3, C4, C5 keep the diaphragm alive (phrenic nerve)
- ✓Three openings: IVC at T8, esophagus at T10, aorta at T12 ('I ate ten eggs at twelve')
- ✓Contraction = flattening = inspiration (increases thoracic volume)
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Common questions about the diaphragm
The phrenic nerve is the primary motor nerve to the diaphragm, arising from the C3, C4, and C5 nerve roots (mainly C4). It also carries sensory fibers from the diaphragm and pericardium.
The three major openings are: the caval opening (T8 level) for the inferior vena cava, the esophageal hiatus (T10 level) for the esophagus and vagus nerves, and the aortic hiatus (T12 level) for the aorta and thoracic duct.
When the diaphragm contracts, it flattens and moves downward. This increases the volume of the thoracic cavity and decreases intrathoracic pressure, causing air to flow into the lungs.
A hiatal hernia occurs when part of the stomach pushes up through the esophageal hiatus into the thoracic cavity. It can cause gastroesophageal reflux symptoms and is common in older adults.