What is the origin of the phrenic nerve?

The phrenic nerve originates from the ventral rami of spinal nerves C3, C4, and C5, with the primary contribution coming from C4. It is a component of the cervical plexus.

What is the course of the phrenic nerve in the neck?

It descends vertically over the anterior surface of the scalenus anterior muscle, crossing it from lateral to medial. Then, it continues downward over the cervical pleura before entering the thoracic cavity.

What does the phrenic nerve innervate?

It provides sole motor innervation to the diaphragm, the main breathing muscle, and sensory innervation to the diaphragmatic pleura, pericardium, and subdiaphragmatic peritoneum.

What is an accessory phrenic nerve?

It is a variant branch from the nerve to subclavius that carries C5 fibres. It runs alongside the main phrenic nerve and typically rejoins it near the first rib.

Why is the accessory phrenic nerve clinically important?

During procedures like phrenic crush to paralyze the diaphragm, if the accessory phrenic nerve is not also crushed, its C5 fibres can bypass the site and maintain diaphragmatic function, undermining the treatment goal.

What is the clinical significance of the phrenic nerve?

It is crucial for respiration as it solely innervates the diaphragm. Historically, procedures like phrenic crush were used to paralyze one side of the diaphragm to rest a diseased lung.

Phrenic Nerve (C3–C5) – Course & Diaphragm Supply