Human Anatomy
Thorax: Joints, Nerves and Applied Anatomy
Thorax anatomy for MBBS: diaphragm and its openings, phrenic nerve, sympathetic chain, thoracic joints and respiration, mapped to NMC codes AN25.1 to AN25.9.
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Thorax: Joints, Nerves and Applied Anatomy
Thorax anatomy for MBBS: diaphragm and its openings, phrenic nerve, sympathetic chain, thoracic joints and respiration, mapped to NMC codes AN25.1 to AN25.9.
This chapter completes the thorax by covering the diaphragm and its openings, the thoracic sympathetic chain and splanchnic nerves, the joints of the thoracic cage and the applied anatomy of the region. It ties together how the thoracic wall and diaphragm work in respiration.
High-yield: Thorax: Joints, Nerves and Applied Anatomy
- The diaphragm is the main muscle of respiration and is supplied by the phrenic nerves from C3, C4 and C5.
- The diaphragm has three large openings: the caval opening at T8, the oesophageal opening at T10 and the aortic opening at T12.
- The caval opening at T8 transmits the inferior vena cava and the right phrenic nerve.
- The oesophageal opening at T10 transmits the oesophagus and the two vagal trunks.
- The aortic opening at T12 transmits the aorta, the thoracic duct and the azygos vein.
- The phrenic nerve is the sole motor supply to the diaphragm, so its injury paralyses that half of the muscle.
- Diaphragmatic irritation refers pain to the shoulder tip because of the shared C3 to C5 supply.
- The thoracic sympathetic chain lies against the necks of the ribs and gives the splanchnic nerves.
- The greater, lesser and least splanchnic nerves carry preganglionic sympathetic fibres to the abdominal ganglia.
- The azygos vein drains the posterior thoracic wall and empties into the superior vena cava.
- The internal thoracic artery runs behind the costal cartilages and gives the anterior intercostal arteries.
- The costovertebral joints connect the heads and tubercles of the ribs to the thoracic vertebrae.
- The intervertebral discs and costal joints give the thoracic cage the mobility needed for breathing.
- The thoracic wall is supplied segmentally by the intercostal nerves, the ventral rami of the thoracic spinal nerves.
Diaphragmatic openings
- **Caval opening (T8):** In the central tendon; transmits the inferior vena cava and the right phrenic nerve.
- **Oesophageal opening (T10):** In the muscular part; transmits the oesophagus and the anterior and posterior vagal trunks.
- **Aortic opening (T12):** Behind the diaphragm; transmits the aorta, thoracic duct and azygos vein.
- **Nerve supply:** Motor supply is the phrenic nerve (C3 to C5); irritation refers pain to the shoulder tip.
NMC competencies in this chapter
- **AN25.1:** Diaphragm: attachments, openings and their contents
- **AN25.2:** Nerve supply and actions of the diaphragm
- **AN25.3:** Thoracic sympathetic chain and splanchnic nerves
- **AN25.4:** Joints of the thoracic cage
- **AN25.5:** Internal thoracic vessels
- **AN25.6:** Azygos system of veins
- **AN25.7:** Movements and mechanics of respiration
- **AN25.8:** Radiographs and surface marking of the thorax
- **AN25.9:** Applied anatomy of the thorax
Frequently Asked Questions
What passes through the three main diaphragmatic openings?
The caval opening at T8 transmits the inferior vena cava and right phrenic nerve, the oesophageal opening at T10 transmits the oesophagus and vagal trunks, and the aortic opening at T12 transmits the aorta, thoracic duct and azygos vein.
Why does diaphragm irritation cause shoulder pain?
The central diaphragm is supplied by the phrenic nerve from spinal roots C3 to C5, which also supply the skin over the shoulder. Irritation of the diaphragm is therefore referred to the shoulder tip.
What are the splanchnic nerves?
The greater, lesser and least splanchnic nerves are branches of the thoracic sympathetic chain. They carry preganglionic sympathetic fibres down to the ganglia that supply the abdominal viscera.
Which nerve supplies motor fibres to the diaphragm?
The phrenic nerve, arising from cervical roots C3, C4 and C5, is the sole motor nerve of the diaphragm. Damage to it paralyses that half of the muscle and raises that dome of the diaphragm.
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