The phrenic nerve
arises from spinal nerves C3, C4 and C5. It provides motor innervation to the diaphragm
and is thus responsible for the act of breathing
. It also provides sensory innervation for many components of the mediastinum and pleura
, as well as the upper abdomen, especially the liver
and gall bladder
. Pain arising from structures served by the phrenic nerve is often "referred" to other somatic regions served by spinal nerves C3-C5. For instance, angina pectoris classically is felt both in the chest and in the left arm. Likewise, a liver abscess close to the diaphragm will be felt in the right shoulder.