Structure and Function of Phrenic Nerve


Phrenic nerve is a mixed motor/sensory nerve which originates from the C3-C5 spinal nerves in the neck. The nerve is significant for breathing since it gives exclusive motor control of the diaphragm, the essential muscle of breath. In people, the right and left phrenic nerves are primarily provided by the C4 spinal nerve,  but there is  contribution from the C3 and C5 spinal nerves. From its starting point in the neck, the nerve ventures descending into the chest to pass between the heart and lungs towards the diaphragm. In addition to motor fibers, the nervus phrenicus comprises sensory fibers, which receive input from the central tendon of the diaphragm and therefore the mediastinal pleura, also as some sympathetic nerve fibers. Although the nerve receives contributions from nerves roots of the plexus cervicalis and therefore the plexus brachialis, it's usually considered break away either plexus. Pain arising from structures supplied by the nervus phrenicus is usually "referred" to other somatic regions served by spinal nerves C3-C5. for instance, a subphrenic abscess beneath the proper diaphragm might cause a patient to feel pain within the right shoulder. Irritation of the nervus phrenicus (or the tissues it supplies) results in the hiccup reflex. A hiccup may be a spasmodic contraction of the diaphragm, which pulls air against the closed folds of the larynx.


The nervus phrenicus originates within the phrenic motor nucleus within the ventral horn of the cervical medulla spinalis. It descends obliquely with the interior vena jugularis across the anterior scalene, deep to the prevertebral layer of deep cervical fascia and therefore the transverse cervical and suprascapular arteries. On the left, the nervus phrenicus crosses anterior to the primary a part of the arteria subclavia. On the proper, it lies on the anterior scalenus and crosses anterior to the 2nd a part of the arteria subclavia. On each side, the nervus phrenicus usually runs posterior to the vena subclavia because it enters the thorax where it runs anterior to the basis of the lung and between the fibrous pericardium and mediastinal pleura
• The right nervus phrenicus passes over the brachiocephalic artery, posterior to the vena subclavia, then crosses the basis of the proper lung anteriorly then leaves the thorax by passing through the vein hiatus opening within the diaphragm at the extent of T8. The proper nervus phrenicus passes over the proper atrium.
• The left nervus phrenicus passes over the pericardium of the ventricle and pierces the diaphragm separately.
The pericardiacophrenic arteries and veins travel with their respective phrenic nerves.
The nervus phrenicus are often marked by a line connecting these two points:
1. 1st point are often labelled 3.5 cm at the extent of the Adam's apple from the midsagittal plane.
2. 2nd point is at the medial end of the clavicle.

Both of those nerves supply motor fibers to the diaphragm and sensory fibers to the fibrous pericardium, mediastinal pleura, and diaphragmatic peritoneum.
Some sources describe the proper nervus phrenicus as innervating the gallbladder, other sources make no such mention. the proper nervus phrenicus can also supply the capsule of the liver.

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Annie Foster
Managing Editor
Journal of Anatomical Science and Research.