The phrenic nerve is an important efferent nerve which innervates the diaphragm, taking part in the medulla oblongata's automatic breathing functions. It also supplies the pericardium with sensitive or afferent fibers. Both the right and left phrenic nerves arises from the third, fourth, and fifth spinal cord cervical roots of the cervical plexus.
Running down vertically through the neck, the superior thoracic aperture, and the mediastinum, both right and left phrenic nerves send motor innervation to the whole diaphragm. They have connections with the breathing centers located in the medulla oblongata.