Recurrent laryngeal nerve

The recurrent laryngeal nerve (RLN) is a branch of the vagus nerve (cranial nerve X) that supplies all the intrinsic muscles of the larynx, with the exception of the cricothyroid muscles. There are two recurrent laryngeal nerves, right and left, in the human body. The right and left nerves are not symmetrical, with the left nerve looping under the aortic arch, and the right nerve looping under the right subclavian artery then traveling upwards. They both travel alongside of the trachea. Additionally, the nerves are one of few nerves that follow a recurrent course, moving in the opposite direction to the nerve they branch from, a fact from which they gain their name. The recurrent laryngeal nerves supply sensation to the larynx below the vocal cords, gives cardiac branches to the deep cardiac plexus, and branches to the trachea, esophagus and the inferior constrictor muscles. The posterior cricoarytenoid muscles, the only muscles that can open the vocal cords, are innervated by this nerve. The recurrent laryngeal nerves are the nerves of the sixth pharyngeal arch. The existence of the recurrent laryngeal nerve was first documented by the physician Galen. The recurrent laryngeal nerves branch from the vagus nerve, relative to which they get their names; the term 'recurrent' from Latin: re- (back) and currere (to run), indicates they run in the opposite direction to the vagus nerves from which they branch. The vagus nerves run down into the thorax, and the recurrent laryngeal nerves run up to the larynx.:930–931 The vagus nerves, from which the recurrent laryngeal nerves branch, exit the skull at the jugular foramen and travel within the carotid sheath alongside the carotid arteries through the neck. The recurrent laryngeal nerves branch off the vagus, the left at the aortic arch, and the right at the right subclavian artery. The left RLN passes in front of the arch, and then wraps underneath and behind it. After branching, the nerves typically ascend in a groove at the junction of the trachea and esophagus.:1346–1347 They then pass behind the posterior, middle part of the outer lobes of the thyroid gland and enter the larynx underneath the inferior constrictor muscle,:918 passing into the larynx just posterior to the cricothyroid joint. The terminal branch is called the inferior laryngeal nerve.:19 Unlike the other nerves supplying the larynx, the right and left RLNs lack bilateral symmetry. The left RLN is longer than the right, because it crosses under the arch of the aorta at the ligamentum arteriosum.:1346–1347 The somatic motor fibers that innervate the laryngeal and pharyngeal muscles are located in the nucleus ambiguus and emerge from the medulla in the cranial root of the accessory nerve. Fibers cross over to and join the vagus nerve in the jugular foramen.:86–88 Sensory cell bodies are located in the inferior jugular ganglion, and the fibers terminate in the solitary nucleus.:86–88 Parasympathetic fibers to segments of the trachea and esophagus in the neck originate in the dorsal nucleus of the vagus nerve. During human and all vertebrate development, a series of pharyngeal arch pairs form in the developing embryo. These project forward from the back of the embryo towards the front of the face and neck. Each arch develops its own artery, nerve that controls a distinct muscle group, and skeletal tissue. The arches are numbered from 1 to 6, with 1 being the arch closest to the head of the embryo, and the fifth arch only existing transiently.:318–323