The Vagus nerve consists of sensory and motor fibers and supplies parasympathetic innervation to the thoracic and abdominal viscera as far distally as the splenic flexure. Peristalsis of the oesophagus, and bowels is in part coordinated by the vagus nerves, as is phonation and the efferent limb of the gag reflex.
The word vagus comes from the Latin word for wanderer. This name is apt, as the 10th cranial nerve provides parasympathetic innervation to all of the viscera as far as the splenic flexure of the colon. The vagus nerve is also known as cranial nerve 10. It arises from the brainstem, the medulla to be precise, below the glossopharyngeal nerve. It emerges lateral to the olive (an ovaloid structure responsible for pathways of motor learning and hearing) and above the inferior cerebellar peduncle. The nerve leaves the skull through the jugular foramen, along with cranial nerves 9 and 11. It is responsible for coordinating peristalsis along with the enteric nervous system, and also enables us to speak, and is the efferent limb of the gag reflex. The vagus nerve has numerous branches that provide motor sensory and taste innervation.
The nucleus ambiguus gives rise to the pharyngeal branches, as well as the inferior and superior laryngeal nerves. The pharyngeal branch consists mainly of the cranial accessory nerve fibers, and gives off notable branches such as the recurrent laryngeal nerve (innervates the muscles of the larynx), and the superior laryngeal nerve (external branch supplies the cricothyroid muscle, internal branch supplies the laryngeal mucosa).
These nerves coordinate phonation and swallowing by innervating the muscles of the pharynx. The dorsal motor nucleus of the vagus nerve supplies parasympathetic innervation to the heart, lungs, oesophagus, stomach, muscles and glands of the digestive tract. The superior and inferior cervical cardiac and thoracic cardiac branches achieve cardiac innervation. The vagus nerve also gives branches to the pulmonary plexus and oesophageal plexus, which supply their respective reasons. The anterior and posterior vagal trunk run in front and behind the lesser curvature of the stomach. The Hering-Breur reflex is also mediated by the vagus nerve and is triggered to prevent over inflation of the alveoli during inspiration. The nucleus spinal tract synapses with the superior vagal ganglion, and gives rise to the auricular branch, which supplies sensation to the external ear, tympanic membrane and meatus. Finally the nucleus tractus solitarius, which synapses with the inferior ganglion, and gives rise to visceral sensing e.g. the carotid and aortic bodies, as well as the cervical, thoracic and abdominal fibers of the nerve. It also has branches, which provides taste sensation to the epiglottis and taste buds.
Vagus nerve Stimulation- This is a procedure that involves the implantation of an electronic device in the chest that stimulates the left vagus nerve (the right is not stimulated as it innervates the heart). This technique is used to treat epilepsy and treatment resistant depression.
Superior laryngeal nerve palsy- This results from damage to the superior laryngeal nerve. The external branch supplies the cricothyroid, which becomes denervated and the pitch of the voice cannot be changed.
Gag reflex- The vagus nerve provides the afferent (motor) limb of the gag reflex. Dysfunction of the nerve therefore leads to a weak or bovine cough.
Aortic sinus baroreceptors- Signals from the baroreceptors (pressure sensitive stretch receptors) in the arch of the aorta travel via the vagus nerve. They travel up the nerve and ultimately terminate in the nucleus tractus solitarius
Developmental precursor- Myelencephalon (secondary vesicle)
Branches- Auricular nerve, superior laryngeal nerve, recurrent laryngeal nerve, pharyngeal nerve, superior and inferior cervical cardiac branches, thoracic cardiac branches, recurrent laryngeal nerve, pulmonary plexus branches, oesophageal plexus branches, anterior and posterior vagal trunks.
Vagus means wanderer, and the nerve wanders as far down as the splenic flexure of the colon to supply parasympathetic innervation
Recall the nagus nerve is the efferent limb of the gag reflex
Recall the vagus neve is the nerve of phonation, va its recurrent and seuperior laryngeal branches
The Vagus nerve is the 10th cranial nerve. It consists of sensory and motor fibers and supplies parasympathetic innervation to the thoracic and abdominal viscera as far distally as the splenic flexure.