Left phrenic nerve

Nervus phrenicus sinister

NervousNervesWhole bodyLeft side

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What it is
Arises mainly from C4 (with C3 and C5) in the neck, runs straight down on the front of the anterior scalene muscle, enters the chest between the subclavian artery and vein and descends over the fibrous pericardium in front of the lung root to the diaphragm. The left nerve crosses the aortic arch and runs over the left ventricle, piercing the diaphragm near the heart apex.
Function
The only motor nerve to its half of the diaphragm (the main breathing muscle); also carries sensation from the central diaphragm, pericardium and mediastinal pleura.
Size
About 2 mm thick; ~33 cm long
Clinical note
Irritation under the diaphragm is felt as shoulder-tip pain (C4 dermatome). A paralysed phrenic nerve - after heart surgery, from a lung tumour or after an interscalene block - leaves one hemidiaphragm high on the chest X-ray.

Part of Cervical plexus

Nearby nervous structures Accessory nerve (CN XI), Brachial plexus, Cardiac plexus, Left recurrent laryngeal nerve, Left vagus nerve (CN X), Right phrenic nerve, Right recurrent laryngeal nerve, Right vagus nerve (CN X), Spinal cord, Spinal dura mater (dural sac)