Phrenic Nerve: Origin, Course And Function - Kenhub

Origin and course

The phrenic nerve is a deep branch of the cervical plexus arising mainly from the C4 spinal nerve, but also receives contributions from C3 and C5 spinal nerves. This fact can be remembered by the mnemonic: C3, 4, 5, keep the diaphragm alive.

The phrenic nerve arises in the neck, at the upper lateral border of the scalenus anterior muscle, and descends along its anterior surface, deep to the prevertebral layer of the deep cervical fascia. The nerve runs posterior to the sternocleidomastoid muscle, the inferior belly of omohyoid muscle, the internal jugular vein, transverse cervical and suprascapular arteries.

From this point on, the pathway of the left and right phrenic nerves has several differences. However, on both sides, the nerves run behind the subclavian vein and anterior to the internal thoracic artery to enter the thoracic cavity through the superior thoracic aperture. In addition, both phrenic nerves are accompanied by the pericardiacophrenic vessels along their course in the thorax.

Left phrenic nerve

Left phrenic nerve Nervus phrenicus sinister 1/4 Synonyms: none

• Passes anteriorly over the first part of the left subclavian artery and deep to the thoracic duct.
• Runs anterior to the hilum of the left lung.
• Crosses anterior to the aortic arch and the vagus nerve.
• Passes over the fibrous pericardium of the left ventricle and pierces the diaphragm close to the apex of the heart to reach the inferior (abdominal) surface of the diaphragm.

Right phrenic nerve

• Descends anteriorly over the second part of the right subclavian artery.
• Passes lateral to the right brachiocephalic vein and the superior vena cava.
• Runs anterior to the hilum of the right lung.
• Passes along the fibrous pericardium of the right atrium and pierces the diaphragm near the inferior vena cava opening.

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