Quick Facts
Origin: The anterior rami of the third, fourth, and fifth cervical nerves.
Course: Inferiorly in the neck, anterior to the anterior scalene, through the thoracic aperture, anterior to the roots of the lungs, lateral to the fibrous pericardium and terminating on the diaphragm.
Branches: Pericardial and phrenicoabdominal branches.
Supply: Motor innervation of the diaphragm; Sensory innervation of the diaphragm, pleura, pericardium, inferior vena cava, and peritoneum.
Origin
The phrenic nerve originates as branches of the anterior rami from the third, fourth, and fifth cervical nerves. These branches coalesce in the neck to form the phrenic nerve.
Course
The right and left phrenic nerves both originate lateral to the upper border of scalenus anterior muscles. They run inferiorly on the anterior surface of the scalenus anterior muscle, posterior to the carotid sheath, before passing between the subclavian arteries and veins (or brachiocephalic veins).
In the thorax, the right phrenic nerve runs down along the brachiocephalic vein, crossing over the anterior surface of the apex of the right lung and the right atrium. It continues down the lateral side of the heart between the fibrous pericardium and the mediastinal pleura to the base of the thorax. Here, terminal branches pierce the respiratory diaphragm before ramifying on the inferior surface of the right side of the diaphragm.
The left phrenic nerve passes between the left subclavian artery and vein (or brachiocephalic vein) over the anterior surface of the aortic arch and apex of the left lung. The left phrenic nerve runs along the left ventricle between the fibrous pericardium and the mediastinal pleura. At the base of the thorax, the left phrenic nerve pierces the muscular diaphragm and ramifies throughout the left half of the respiratory diaphragm (Standring, 2016).
Branches
The only two named branches of the phrenic nerve are the pericardial and phrenicoabdominal branches of the phrenic nerve.
Supplied Structures & Function
The phrenic nerve is a mixed motor and sensory nerve. The bulk of the phrenic nerve innervates the respiratory diaphragm, the major muscle of respiration. The right phrenic nerve innervates the right side of the diaphragm, while the left phrenic nerve innervates the left side of the diaphragm.
The phrenic nerve provides sensory innervation to several tissues. It innervates the respiratory diaphragm and its central tendon, the pericardium, the mediastinal and diaphragmatic pleura, and portions of the diaphragmatic peritoneum.
List of Clinical Correlates
—Referred pain
—Phrenic nerve palsy
—Hiccups
References
Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edn.: Elsevier Limited.
