The phrenic nerves provide the major nerve supply to the diaphragm because of their embryonic association with the septum transversum that goes on to form the central tendinous part of the diaphragm.
Also, it supplies a large percentage of the median structures of the mediastinum i.e. it is sensory for:
- central parts of diaphragmatic
- superficial serous pericardium
- abdominal components e.g.:
- superior peritoneum
Each phrenic nerve contributes predominantly motor fibres solely to its hemidiaphragm. Damage to the phrenic nerve may lead to paralysis of one hemidiaphragm. It has a few sensory fibres which supply all but the peripheral attachments of the muscle. Irritation of the phrenic sensory fibres tends to refer pain to the C4 dermatome territory.
The passage taken by the right and left phrenic nerves through the thorax is different. This is largely due to the disposition of great vessels within the mediastinum.
Occasionally, the phrenic nerve may be joined by an accessory phrenic nerve.