phrenic nerve, one of a pair of branches of the cervical plexus, arising from the first four cervical nerves and passing to the diaphragm. It contains about half as many sensory as motor fibers and is generally known as the motor nerve to the diaphragm, although the lower thoracic nerves also help innervate the diaphragm. The pleural branches of the phrenic nerve are very fine filaments supplying the mediastinal pleura. The pericardial branches are delicate filaments passing to the upper pericardium. The terminal branches diverge after passing separately through the diaphragm and are distributed on the abdominal surface of the diaphragm. On the right side, a branch near the inferior vena cava communicates with the phrenic plexus in association with a phrenic ganglion. There is no phrenic ganglion on the left side. Also called internal respiratory nerve of Bell. Compare accessory phrenic nerve.
