Phrenic Nerve - Path

Path

The phrenic nerve descends obliquely with the Internal Jugular Vein across the anterior scalene, deep to the prevertebral layer of deep cervical fascia and the transverse cervical and suprascapular arteries. On the left, the phrenic nerve crosses anterior to the first part of the subclavian artery. On the right, it lies on the anterior scalene muscle and crosses anterior to the 2nd part of the subclavian artery. On both sides, the phrenic nerve runs posterior to the subclavian vein and anterior to the internal thoracic artery as it enters the thorax where it runs anterior to the root of the lung and into the pericardium between the fibrous and parietal layers.

Found in the middle mediastinum, both phrenic nerves run from C3, C4, and C5 along the anterior scalene muscle deep to the carotid sheath.

• The right phrenic nerve passes over the brachiocephalic artery, posterior to the subclavian vein, and then crosses the root of the right lung anteriorly and then leaves the thorax by passing through the vena cava hiatus opening in the diaphragm at the level of T8. The right phrenic nerve passes over the right atrium.
• The left phrenic nerve passes over the pericardium of the left ventricle and pierces the diaphragm separately.

Both of these nerves supply motor fibres to the diaphragm and sensory fibres to the fibrous pericardium, mediastinal pleura, and diaphragmatic peritoneum.

The pericardiacophrenic arteries and veins travel with their respective phrenic nerves.

The contribution of the 5th cervical nerve may stem from an accessory phrenic nerve. Most often it is a branch of the nerve to the subclavius and may contain numerous phrenic nerve fibers. If the accessory phrenic nerve is present, it lies lateral to the main nerve and descends posterior and occasionally inferior to the subclavian vein. The accessory phrenic nerve connects to the phrenic nerve in the thorax or the root of the neck.