Describe the diaphragm under origin, openings, nerve supply and actions. Add a note on its applied anatomy.

Definition

Origin — Three Parts

• All fibres converge into the central tendon, a trefoil-shaped aponeurosis with no bony attachment
• Median arcuate ligament — joins the two crura in front of the aorta
• Medial arcuate ligament — over psoas major; lateral arcuate ligament — over quadratus lumborum
• The right dome rises higher (to the 4th intercostal space) because of the liver; the left reaches the 5th

Openings

• Mnemonic — "I ate (8) ten (10) eggs at twelve (12)": vena cava at 8, oesophagus at 10, aorta at 12
• Also — the left phrenic nerve pierces the muscle separately; the greater and lesser splanchnic nerves pierce the crura; the sympathetic chain passes behind the medial arcuate ligament

Nerve Supply

• Motor — entirely by the phrenic nerve (C3, C4, C5). Mnemonic — "C3, 4, 5 keep the diaphragm alive"
• Sensory — the central part by the phrenic; the peripheral part by the lower six intercostal nerves
• Each half is supplied by its own phrenic nerve, so one half can be paralysed alone

Actions

• Also assists in — coughing, sneezing, vomiting, micturition, defaecation and parturition, by raising intra-abdominal pressure together with the abdominal muscles
• Weight-lifting — a fixed diaphragm with a closed glottis (Valsalva) stabilises the trunk
• Assists venous return — the "thoraco-abdominal pump"

Relations

• Above — pleura and lungs, pericardium and heart
• Below — liver, stomach and spleen; also the kidneys and suprarenals
• Blood supply — musculophrenic, pericardiacophrenic, superior and inferior phrenic arteries, and the lower intercostals

Development of the Diaphragm

• Failure of the pleuroperitoneal membrane to close leaves the foramen of Bochdalek, usually posterolateral and on the left — the commonest congenital diaphragmatic hernia
• Foramen of Morgagni — a rarer anterior defect between the sternal and costal origins

Applied Aspects

• Referred pain to the shoulder tip (C4) — from irritation of the central diaphragmatic pleura or peritoneum: subphrenic abscess, ruptured spleen, ectopic pregnancy, and after laparoscopy from retained gas
• Phrenic nerve palsy — from bronchial carcinoma, surgery or a neck lesion; causes a raised hemidiaphragm with paradoxical upward movement on sniffing
• Hiatus hernia — herniation of the stomach through the oesophageal opening; sliding (95%, causes reflux) or rolling (para-oesophageal), which may strangulate
• Congenital diaphragmatic hernia — usually through the foramen of Bochdalek posterolaterally on the left; abdominal viscera enter the chest and cause pulmonary hypoplasia
• Hiccup is a spasmodic contraction of the diaphragm with sudden glottic closure, mediated by the phrenic nerve
• Subphrenic abscess collects in the space between the diaphragm and the liver, and classically causes shoulder tip pain with a sympathetic pleural effusion above it — "pus somewhere, pus nowhere, pus under the diaphragm"
• Diaphragmatic rupture after blunt trauma is commoner on the left, since the liver protects the right; bowel may be seen in the chest on radiography
• Eventration — a congenitally thin, mostly membranous hemidiaphragm that is permanently elevated but, unlike palsy, remains continuous
• The diaphragm is the muscle of respiration that never rests, and its fatigue is a terminal event in respiratory failure
• Diaphragmatic movement is assessed clinically by percussing the level of dullness in full inspiration and expiration — normally 4 to 5 cm of excursion
• Upper abdominal surgery splints the diaphragm and predisposes to basal atelectasis, which is why early mobilisation and breathing exercises matter
• Foramen of Morgagni hernia presents later in life, is usually right-sided and anterior, and often contains omentum or transverse colon
• Phrenic nerve crush was once used deliberately to rest a tuberculous lung, an obsolete operation that illustrates the exclusive motor role of the nerve
• The diaphragm receives its motor supply from the neck, a fact explained only by its development — a good illustration of why embryology is taught alongside gross anatomy