Vagus nerve stimulation (VNS) therapy

VNS may be achieved by one of the vagal manoeuvres: holding the breath for 20–60 seconds, dipping the face in cold water, coughing, or tensing the stomach muscles as if to bear down to have a bowel movement. Patients can train themselves to perform vagal manoeuvres (or find one or more on their own).

The Latin word vagus means literally "wandering" (the words vagrant, vagabond, vague, and divagation come from the same root). Sometimes the right and left branches together are spoken of in the plural and are thus called vagi. The vagus was also historically called the pneumogastric nerve since it innervates both the lungs and the stomach.

Upon leaving the medulla oblongata between the olive and the inferior cerebellar peduncle, the vagus nerve extends through the jugular foramen, then passes into the carotid sheath between the internal carotid artery and the internal jugular vein down to the neck, chest, and abdomen, where it contributes to the innervation of the viscera, reaching all the way to the colon. Besides giving some output to various organs, the vagus nerve comprises between 80% and 90% of afferent nerves mostly conveying sensory information about the state of the body's organs to the central nervous system. The right and left vagus nerves descend from the cranial vault through the jugular foramina, penetrating the carotid sheath between the internal and external carotid arteries, then passing posterolateral to the common carotid artery. The cell bodies of visceral afferent fibres of the vagus nerve are located bilaterally in the inferior ganglion of the vagus nerve (nodose ganglia).

The right vagus nerve gives rise to the right recurrent laryngeal nerve, which hooks around the right subclavian artery and ascends into the neck between the trachea and oesophagus. The right vagus then crosses anterior to the right subclavian artery, runs posterior to the superior vena cava, descends posterior to the right main bronchus, and contributes to cardiac, pulmonary, and oesophagal plexuses. It forms the posterior vagal trunk at the lower part of the oesophagus and enters the diaphragm through the oesophagal hiatus.

The left vagus nerve enters the thorax between the left common carotid artery and left subclavian artery and descends on the aortic arch. It gives rise to the left recurrent laryngeal nerve, which hooks around the aortic arch to the left of the ligamentum arteriosum and ascends between the trachea and oesophagus. The left vagus further gives off thoracic cardiac branches, breaks up into the pulmonary plexus, continues into the oesophagal plexus, and enters the abdomen as the anterior vagal trunk in the oesophagal hiatus of the diaphragm.

The vagus nerve includes axons which emerge from or converge onto four nuclei of the medulla:

1. The dorsal nucleus of vagus nerve – which sends parasympathetic output to the viscera, especially the intestines
2. The nucleus ambiguus – which gives rise to the branchial efferent motor fibres of the vagus nerve and preganglionic parasympathetic neurons that innervate the heart
3. The solitary nucleus – which receives afferent taste information and primary afferents from visceral organs
4. The spinal trigeminal nucleus – which receives information about deep/crude touch, pain, and temperature of the outer ear, the dura of the posterior cranial fossa and the mucosa of the larynx