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The phrenic nerve is formed by\u00a0C4 cervical spinal nerve, with contributions from C3 and C5.<\/p>\n\n\n\n
- Its stimulation causes a gradual contraction of the diaphragm leading to inspiration.
- Involuntary, passive expiration is completely passive (without nervous stimulation)<\/li><\/ul><\/li>
- Since there are two phrenic nerves innervating the diaphragm, each nerve is responsible for its own side of the diaphragm and can work independently (although they are synchronized at the level of the brain-stem).<\/li>
- Besides the motor innervation, it also provides\u00a0sensory innervation to the pericardium and the mediastinal pleura<\/strong>
- Pain sensations conveyed by this nerve usually radiate to the skin above the clavicle.<\/li><\/ul><\/li>
- The phrenic nerves enter the superior mediastinum between the subclavian artery and the branching point of the brachiocephalic vein. From there, they run in\u00a0parallel to the vagus<\/strong>.<\/li><\/ul>\n\n\n\n
Tip:<\/strong> In order to distinguish between the phrenic and the vagus, remember that the vagus goes posteriorly<\/strong> while the phrenic goes anteriorly<\/strong> to the root of the lung.<\/em><\/p>\n\n\n\n
Left phrenic nerve<\/h4>\n<\/span>\n\n\n
- Descends between the left common carotid and the left subclavian arteries parallel to the vagus<\/strong><\/li>
- When it reaches the arch of the aorta it crosses at the left side of the arch anteriorly to the left vagus nerve and passes more superficially to the left superior intercostal vein<\/li>
- The left phrenic nerve passes anteriorly to the root of the left lung<\/strong> and runs along the pericardium while innervates it<\/li>
- Just below the pericardium it passes through the diaphragm on the left side and innervates it<\/li><\/ol>\n\n\n<\/span>\n
Right phrenic nerve<\/h4>\n<\/span>\n\n\n
- Runs along the right side of the right brachiocephalic vein, superior vena cava, and the pericardium<\/strong> superficial to the right atrium<\/li>
- Like the left phrenic, the right phrenic runs anterior to the root of the right lung continues downwards on the right side of the inferior vena cava below the pericardium on the right side to the diaphragm<\/li>
- Pierces the diaphragm near the caval opening (the foramen for the inferior vena cava)<\/strong><\/li><\/ol>\n\n\n\n
![\"\"](\"http:\/\/meddists.com\/wp-content\/uploads\/2018\/09\/800px-Trachea.jpg\")
Vagus and recurrent laryngeal nerves<\/strong> \u2014 Adapted from the work of Anatomist90 \u2014 CC BY-SA 3.0<\/figcaption><\/figure><\/div>\n\n\n\n ![\"\"](\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2020\/12\/recurrent-laryngeal.png\")
The left vagus and recurrent laryngeal nerves<\/strong><\/figcaption><\/figure>\n<\/span>
- Descends between the left common carotid and the left subclavian arteries parallel to the vagus<\/strong><\/li>