The phrenic nerve is a bilateral, mixed nerve that originates from the cervical nerves in the neck and also descends v the thorax to innervate the diaphragm.

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It is the only resource of engine innervation come the diaphragm and also therefore theatre a critical role in breathing.

In this article, we chandelier look in ~ the anatomy the the phrenic nerve – that anatomical course, motor and also sensory functions.


Overview

Nerve root – anterior rami the C3, C4 and also C5.Sensory functions – innervates the central part the the diaphragm, the pericardium and the mediastinal part of the parietal pleura.

Anatomical Course

The phrenic nerve originates native cervical spinal roots C3, C4 and C5 . This have the right to be remembered utilizing the limerick “C3, 4 and 5 keep the diaphragm alive”. Spinal source C4 provides the main contribution, v lesser contributions from C3 and C5 and some communicating fibres native the cervical plexus.

The nerve occurs at the lateral border of the anterior scalene muscle. It climate passes inferiorly over the anterior surface ar of anterior scalene, deep come the prevertebral layer of cervical fascia. Top top both sides, the nerve operation posterior to the subclavian vein. From here, the course of the phrenic nerve differs in between the left and also right:

Right Phrenic Nerve

Passes anteriorly over the lateral part of the right subclavian artery.Enters the thorax via the superior thoracic aperture.Descends anteriorly along the appropriate lung root.Courses follow me the pericardium that the best atrium the the heart.Pierces the diaphragm in ~ the worse vena cava opening.Innervates the inferior surface of the diaphragm.

Left Phrenic Nerve

Passes anteriorly over the medial component of the left subclavian artery.Enters the thorax via the remarkable thoracic aperture.Descends anterior come the left lung root.Crosses the aortic arch and bypasses the vagus nerve.Courses along the pericardium of the left ventricle.Pierces and also innervates the inferior surface ar of the diaphragm.
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Fig 1 – The origin of the phrenic nerve indigenous the anterior rami the C3,4 and also 5.


Motor Functions

The phrenic nerve provides motor innervation to the diaphragm; the main muscle of respiration.

As the phrenic nerve is a bilateral structure, every nerve supplies the ipsilateral side of the diaphragm (the hemi-diaphragm on the same side as itself).


Sensory Functions

Sensory fibres indigenous the phrenic nerve supply the central part of the diaphragm, consisting of the surrounding pleura and peritoneum. The nerve likewise supplies sensation to the mediastinal pleura and the pericardium.


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Fig 2 – The anatomical course of the phrenic nerves, i m sorry innervate the diaphragm.


Clinical Relevance: Diaphragmatic Paralysis

The phrenic nerve provides motor innervation to the diaphragm. If the nerve i do not care damaged, paralysis the the diaphragm can result. Causes of phrenic nerve palsy include:

Mechanical trauma – ligation or damage to the nerve during surgery.Compression – due come a tumour within the chest cavity.Neuropathies – such diabetic neuropathy.

Paralysis of the diaphragm produce a paradoxical movement. The impacted side the the diaphragm moves upwards during inspiration, and also downwards during expiration. A unilateral diaphragmatic paralysis is typically asymptomatic and is most frequently an incidental finding on x-ray. If both sides space paralysed, the patient may experience bad exercise tolerance, orthopnoea and also fatigue. Lung function tests will show a restrictive deficit.

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Management that diaphragmatic paralysis is two-fold. Firstly, the underlying reason must be identified and treated (if possible). The second component of treatment deals with symptomatic relief. This is commonly via non-invasive ventilation, such as a CPAP (continuous hopeful airway pressure).