The phrenic nerve is a bilateral, mixed nerve the originates indigenous 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 motor innervation to the diaphragm and therefore theatre a vital role in breathing.

In this article, we candlestick look at the anatomy of the phrenic nerve – that is anatomical course, motor and also sensory functions.


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

Anatomical Course

The phrenic nerve originates native cervical spinal roots C3, C4 and also C5 . This have the right to be remembered making use of the limerick “C3, 4 and 5 store the diaphragm alive”. Spinal source C4 provides the main contribution, v lesser contribute from C3 and C5 and some connecting fibres indigenous the cervical plexus.

The nerve arises at the lateral border the the anterior scalene muscle. It climate passes inferiorly over the anterior surface ar of anterior scalene, deep to the prevertebral layer of cervical fascia. ~ above both sides, the nerve runs posterior come the subclavian vein. From here, the food of the phrenic nerve differs in between the left and right:

Right Phrenic Nerve

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

Left Phrenic Nerve

Passes anteriorly over the medial part of the left subclavian artery.Enters the thorax via the exceptional thoracic aperture.Descends anterior come the left lung root.Crosses the aortic arch and bypasses the vagus nerve.Courses along the pericardium that the left ventricle.Pierces and innervates the inferior surface of the diaphragm.

Fig 1 – The origin of the phrenic nerve indigenous the anterior rami of C3,4 and 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, each nerve supplies the ipsilateral side of the diaphragm (the hemi-diaphragm ~ above the same side as itself).

Sensory Functions

Sensory fibres native the phrenic nerve it is provided the main part of the diaphragm, including the surrounding pleura and peritoneum. The nerve also supplies emotion to the mediastinal pleura and the pericardium.


Fig 2 – The anatomical course of the phrenic nerves, i beg your pardon innervate the diaphragm.

Clinical Relevance: Diaphragmatic Paralysis

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

Mechanical trauma – ligation or damages to the nerve during surgery.Compression – due to a tumour in ~ the chest cavity.Neuropathies – such diabetic neuropathy.

Paralysis the the diaphragm produces a paradoxical movement. The influenced side of the diaphragm move upwards throughout inspiration, and also downwards throughout expiration. A unilateral diaphragmatic paralysis is normally asymptomatic and is most often an incidental recognize on x-ray. If both sides space paralysed, the patient might experience bad exercise tolerance, orthopnoea and fatigue. Lung role tests will show a restrictive deficit.

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Management of diaphragmatic paralysis is two-fold. Firstly, the underlying cause must be identified and treated (if possible). The second part of treatment faces symptomatic relief. This is commonly via non-invasive ventilation, such together a CPAP (continuous positive airway pressure).