Diaphragm
Thorax · Trunk
The diaphragm is the dome-shaped musculotendinous sheet that separates the thoracic cavity from the abdominal cavity and serves as the principal muscle of breathing. It has three origins: a sternal part from the posterior surface of the xiphoid process, a costal part from the inner surfaces of the lower six ribs, and a lumbar part from the crura arising off the upper lumbar vertebrae and from the arcuate ligaments. All of these fibres converge on the central tendon, the flat aponeurosis at the top of the dome. When it contracts, the dome flattens and descends, increasing the vertical diameter of the thorax and drawing air into the lungs, making it the primary muscle of inspiration. It is supplied by the phrenic nerve (C3, C4, C5). Structures such as the aorta, oesophagus, and inferior vena cava pass through it at distinct openings.
Origin, Insertion, Action & Nerve
Origin
Sternal part: posterior surface of xiphoid process; Costal part: inner surfaces of lower 6 ribs (7–12); Lumbar part: crura from L1–L3 and arcuate ligaments
Insertion
Central tendon of the diaphragm
Action
Primary muscle of inspiration; increases vertical diameter of the thorax
Nerve
Phrenic nerve (C3, C4, C5)
Attachments explained
The Diaphragm is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Sternal part: posterior surface of xiphoid process; Costal part: inner surfaces of lower 6 ribs (7–12); Lumbar part: crura from L1–L3 and arcuate ligaments
Insertion
Central tendon of the diaphragm
Action & function
When the Diaphragm contracts, it produces the following movements: Primary muscle of inspiration; increases vertical diameter of the thorax.
As part of the Thorax group of the Trunk, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Diaphragm receives its nerve supply from the Phrenic nerve (C3, C4, C5). This nerve carries fibres from spinal segment(s) C3, C4, C5.
Because a muscle can only contract when its nerve is intact, injury to the Phrenic nerve or to its spinal roots (C3, C4, C5) can weaken or paralyse the Diaphragm, impairing the movements it normally produces (primary muscle of inspiration). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Diaphragm (the OIANS method)
Study the diaphragm as a dome anchored around its rim to the sternum, ribs, and lumbar vertebrae, all pulling toward the fixed central tendon. Because the muscle fibres shorten toward that tendon, contraction flattens the dome downward, enlarging the chest vertically, so picturing the piston-like descent explains why it is the main muscle of inspiration.
Lock in the innervation with the classic rhyme, C3, 4, 5 keep the diaphragm alive, which also explains why high cervical spinal cord injuries are so dangerous. Remembering that the phrenic nerve descends a long way from the neck to reach it accounts for referred shoulder pain when the diaphragm is irritated, a memorable clinical tie between origin, action, and nerve.
Frequently asked questions
Where is the Diaphragm located?
The Diaphragm is a muscle of the Thorax group, located in the Trunk.
What is the origin of the Diaphragm?
Sternal part: posterior surface of xiphoid process; Costal part: inner surfaces of lower 6 ribs (7–12); Lumbar part: crura from L1–L3 and arcuate ligaments
What is the insertion of the Diaphragm?
Central tendon of the diaphragm
What movements does the Diaphragm produce?
Primary muscle of inspiration; increases vertical diameter of the thorax
What nerve supplies the Diaphragm?
Phrenic nerve (C3, C4, C5)
Is the Diaphragm free to study in OIANS?
The Diaphragm is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Trunk is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
Study the Diaphragm
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