Phrenic nerve Anatomy & Definition
Phrenic nerve arises in neck region from the anterior rami of the 3rd, 4th, and 5th cervical spinal nerves. Phrenic nerve roots are (C3C4C5) but mainly from the fourth cervical spinal segment root and recive contribution from third and forth cervical nerves. The nerve passes down through the thorax to innervate diaphragm and its associated membranes. Besides diaphragm motor and sensory innervations in Thorax the phrenic nerves provide innervation through somatic afferent fibers to the
- Mediastinal pleura
- Fibrous pericardium
- Parietal layer of serous pericardium
The phrenic nerve has both sensory and motor originate in cervical plexus. Phrenic nerves are two in number and have sympathetic nerve fibers. It possess efferent and afferent fibers. The efferent fibers are the sole nerve supply to the muscle of the diaphragm. Blood supply is pericardiophrenic artery which is branch of internal thoracic artery.
Phrenic nerve course:
The phrenic nerves are branches of the cervical plexus and arise on each side. It descends down to the thorax by passing around the upper lateral border of each anterior scalene muscle. The phrenic nerves continue inferiorly across the anterior surface of each anterior scalene muscle within the prevertebral layer of cervical fascia. From here the nerves leave the lower edge of the anterior scalene muscle each phrenic nerve passes between the subclavian vein and artery to enter the thorax and continue to the diaphragm. The left and right phrenic nerve each have different course down to diaphragm.
Right phrenic nerve
The right phrenic nerve enters to the superior mediastinum and lateral to the right vagus nerve. It is slightly posterior to the beginning of the right brachiocephalic vein. Right phrenic nerve continues inferiorly along the right side brachiocephalic vein and the right side of the superior vena cava. It passes in front of the root of the right lung and runs along the right side of the pericardium, which separates the nerve from the right atrium. It then descends on the right side of the inferior vena cava to the diaphragm. The pericardiacophrenic vessels accompany it through most of its course in the thorax. The right phrenic nerve descends on the right side of the inferior vena cava to the diaphragm.
Left phrenic nerve
The left phrenic nerve enters the superior mediastinum in a position similar to the path taken by the right phrenic nerve. Left phrenic nerve lies lateral to the left vagus nerve and lateral and slightly posterior to the beginning of the left brachiocephalic vein. It continuous to descend across the left lateral surface of the arch of aorta, passing superficially to the left vagus nerve and the left superior intercostals vein. It passes in front of the root of the left lung and then descends over the left surface of the pericardium, which separates the nerve from the left ventricle and is accompanied by the pericardiacophrenic vessels. On reaching the diaphragm, the left this nerve terminal branches pierce the muscle and supply the central part of the peritoneum on its underaspect.
Phrenic nerve function
Phrenic nerve serve important function of both sensory and motor supply to the diaphragm and pleural and mediastinal viscera
Moter supply: diaphragm
Sensory supply: Mediastinal pleura, Fibrous pericardium, Parietal layer of serous pericardium
Phrenic nerve damage
Phrenic nerve is connection between brain and diaphragm which control breathing. When phrenic nerve is damage this control of breathing is lost. The nerves pass down having close proximity with trachea, heart vessels, and lungs. Any condition or disease involving these organ may damage and interrupt signaling and problem in breathing.
Causes of phrenic nerve damage
When there is phrenic nerve injury it interrupts breathing result in shortness of breath and cessation of normal breathing. Different causes of phrenic nerve damage are
- Spinal cord injury
- Surgical trauma
- Physical damage
- Disease/Condition of proximity organ
Sign and symptoms of the phrenic nerve damage are obvious when there is bilateral damage. Patient with phrenic nerve damage can present with chest pain, cough, and dyspnea.
Treatment of phrenic nerve damage includes surgical intervention if the patient has bilateral diaphragmatic paralysis. There are various options include placation and phrenic nerve stimulation. Phrenic nerve stimulation is a surgical procedure in which an electrical device is implanted in diaphragm. This device rhythmically contract diaphragm. Phrenic nerve placation is procedure for paralyzed diaphragm in which there is pacing and nerve graft to improve breathing. Asymptomatic and unilateral diaphragmatic paralysis requires no treatment and underlying cause is treated.
Paralysis of the diaphragm
The phrenic nerves possess efferent and afferent fibers. The efferent fibers are the sole nerve supply to the muscle of the diaphragm. It gives somatic nerve supply to diaphragm through anterior rami of C3-C5. The nerve may be paralyzed because of pressure from malignant tumors in the mediastinum. Surgical crushing or sectioning of the nerve in the neck, producing paralysis of the diaphragm on one side, this technique was used as part of the treatment of lung tuberculosis, especially of the lower lobes. The immobile dome of the diaphragm rests the lung.
Phrenic nerve pain
Phrenic nerve pain arises from the structures supplied by the phrenic nerve. The pain is often referred to other regions which are supplied by spinal nerves C3-C5. For example when there is infection beneath diaphragm, the pain is felt in the shoulder region. Nerve irritation causes hiccup reflex. Hiccup is spasmodic contraction in diaphragm muscle; this contraction pulls air against closed folds of the larynx.
Phrenic nerve variation
- Accessory phrenic nerve arise from ansa cervicalis or subclavian nerve. C5 cervical nerve may be stem from an accessory phrenic nerve. If this accessory nerve is present it is present lateral to the main phrenic nerve and decends posteriorly to subclavian vain.
- It may give nerve supply to the subclavius muscle.
- Its variant can receive additional branches from brachial and cervical plexus
Phrenic nerve cadaver
In cadavers phrenic nerve is dissected to clarify the course and anatomical landmarks in the neck region. In dissection nerve arise in posterior triangle of neck. It crosses the anterior scalene muscle near Erb’s point in supraclavian triangle.
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