Phrenic n.

The phrenic nerve is a nerve that originates in the neck and passes down between the lung and heart to reach the diaphragm. It is important for breathing, as it supplies motor innervation to the diaphragm and receives sensory information from it. There are two phrenic nerves, a left and a right one.

The phrenic nerve originates mainly from the 4th cervical nerve, but also receives contributions from the 5th and 3rd cervical nerves (C3-C5) in humans. Thus, the phrenic nerve receives innervation from parts of both the cervical plexus and the brachial plexus. To remember which spinal nerves contribute to the phrenic nerve, remember that C3, 4, and 5 keep the diaphragm alive! 

The phrenic nerves contain motor, sensory, and sympathetic nerve fibers. These nerves provide the only motor supply to the diaphragm as well as sensation from the central tendon of the diaphragm. In the thorax, each phrenic nerve also supplies the mediastinal parietal pleura and the parietal pericardium.