Accessory phrenic nerves

The accessory phrenic nerve is a small nerve typically originating from the fifth cervical nerve (C5), though it may also arise as a branch splitting from the nerve to the subclavius (C5), which often merges with the phrenic nerve.

Once formed, the accessory phrenic nerve runs parallel to the phrenic nerve and may join it either along its course through the thoracic cavity or just before the phrenic nerve reaches the diaphragm. Functionally, the accessory phrenic nerve contributes to the motor and sensory innervation of the diaphragm, acting as a supplement to the primary input from the phrenic nerve.

Injury to the accessory phrenic nerve could potentially affect diaphragm function; however, the phrenic nerve remains primarily responsible for the diaphragm's innervation and function.