The recurrent laryngeal nerve is a branch of the vagus nerve (CN X). Running within the endoneurium, it innervates the laryngeal muscles in the neck and pick up sensory information from the larynx, which is where vocal cords are. The recurrent laryngeal nerve has a long and rambling route; originating in the brainstem, the left recurrent laryngeal nerve branches off the vagus nerve and travels down into the thorax (chest) to loop around under the arch of the aorta artery, then it goes back up to supply the larynx. On the other hand, the right branch loops around the right subclavian artery before going back up.
As the recurrent laryngeal nerve loops around the aorta or subclavian artery, it gives off several cardiac filaments to the deep part of the cardiac plexus. As it ascends into the neck it gives off branches, more numerous on the left than on the right side, to the mucous membrane and muscular coat of the oesophagus; branches to the mucous membrane and muscular fibers of the trachea; and some pharyngeal filaments to the superior pharyngeal constrictor muscle.
The nerve is best known for its importance in thyroid surgery, as it runs immediately posterior to this gland. If it is damaged during surgery, the patient will have a hoarse voice. Nerve damage can be assessed by laryngoscopy, during which a stroboscopic light confirms the absence of movement in the affected side of the vocal cords.