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Phrenic nerve

Recommended video: Nerve roots of the phrenic nerve [00:58]
Mnemonic to help you remember the nerve roots of the phrenic nerve.

The phrenic nerve is a mixed nerve arising from the anterior rami of C3-C5 spinal nerves, which are components of the cervical plexus. It arises in the neck and descends vertically through the thorax to end on the diaphragm. The phrenic nerve is a bilateral nerve, and its left and right counterparts have some important differences in terms of course and relations with surrounding structures.

The main function of the phrenic nerve is to provide the entire motor innervation to the diaphragm, which makes it a vital component in the physiology of breathing. In addition, the phrenic nerve supplies sensory innervation to the central part of the diaphragm and adjacent fascial coverings.

This article will discuss the anatomy and function of the phrenic nerve.

Key facts about the phrenic nerve
Origin C3-C5 spinal nerves
Supply Motor: Diaphragm
: Central part of diaphragm, pericardium, mediastinal pleura, diaphragmatic pleura, diaphragmatic peritoneum
  1. Origin and course
    1. Left phrenic nerve
    2. Right phrenic nerve
  2. Function
  3. Clinical relations
    1. Phrenic nerve damage
  4. Sources
+ Show all

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.

This image shows the left and right phrenic nerve in a cadaver, along with surrounding neurovascular structures.

Left phrenic nerve

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.


The phrenic nerve is a mixed nerve, carrying motor, sensory and sympathetic fibers. It is the only nerve that provides motor innervation to the diaphragm, with the left and right phrenic nerves innervating their corresponding ipsilateral hemidiaphragms. Thus, the phrenic nerve stimulates the movements of the diaphragm and plays a crucial role in breathing.

The phrenic nerve also provides sensory innervation to the central part of the diaphragm, as well as the pericardium, mediastinal pleura, diaphragmatic pleura and diaphragmatic peritoneum.

Pro tip: To solidify your understanding of a newly learned topic, quiz yourself. Find out why anatomy quiz questions are the secret to your success!

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