Phrenic nerve-the phrenic nerve is formed from contributions from the c3, 4, and 5 ventral primary rami. it lies on the anterior scalene muscle, immediately deep to the subclavian vein. since the phrenic nerve innervates the diaphragm, the patients symptom (difficulty breathing) fits with an injury to the phrenic nerve.the external branch of the superior laryngeal nerve travels with the superior thyroid artery to innervate the cricothyroid muscle. it is found medial to the scalene muscles. the recurrent laryngeal nerves are branches of the vagus that branch in the thorax. the right recurrent laryngeal loops around the subclavian artery and the left recurrent laryngeal loops around the aortic arch. then, the two nerves ascend to the larynx, running medial to the scalenes. the sympathetic trunk lies in the prevertebral fascia behind the carotid sheath and in front of the prevertebral muscles. finally, the vagus nerve runs in the carotid sheath, superficial to the scalene muscles.
