- These are a pair of mixed nerves and provide sole motor supply to the diaphragm. Each nerve has following functional components :-
- Motor: - To the entire diaphragm.
- Sensory: Central part of diaphragm (proprioceptive), pain from pericardium, mediastinal and diaphragmatic pleura, and peritoneum on the under surface of diaphragm (diaphragmatic peritoneum).
- Sympathetic fibers: - Postganglionic and vasomotor in function.
- Phrenic nerve is formed by anterior rami of C3, C4, C5with C4being the major contributor. Each nerve is formed in neck at lateral border of scalenusanterior and descends in front of scalenusanteriorand behind prevertebrallayer of deep cervical fascia. Each nerve enters thorax by passing in front of subclavianarteryand behind beginning ofbrachiocephalic vein. Both nerve pass in front of root or hilum of lungand then have different course in the thorax :-
Right phrenic nerve is shorter and more vertical. It descends along right side of venous system, i.e. right
Left phrenic nerve descends along left side of arterial system, i.e. left subclavian artery, aortic arch, left vagus and pericardium. It pierces the muscular part of diaphragm (left cupola) in front ofthe central tendon, and joins with left phrenic sympathetic plexus without forming a ganglion.
Sympathetic component of phrenic nerve
- Phrenic ganglion of right side gives twigs to right suprarenal gland, IVC, falciform and coronary ligaments of the liver, and sometimes gall-bladder. Phrenic plexus (not ganglion) on left side gives twigs to left suprarenal gland only.
- Sometimes C5 nerve forms accessory phrenic nerve and joins the phrenic nerve in thorax via nerve to subclavius.