The vagus is the longest nerve of the autonomic nervous system in the human body and comprises both sensory and motor fibers.

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.

[5] The vagus nerve supplies motor parasympathetic fibers to all the organs (except the adrenal glands) from the neck down to the second segment of the transverse colon.

It also has some afferent fibers that innervate the inner (canal) portion of the outer ear (via the auricular branch, also known as Arnold's or Alderman's nerve) and part of the meninges.

At this location, neuroscientist Otto Loewi first demonstrated that nerves secrete substances called neurotransmitters, which have effects on receptors in target tissues.

Research has shown that women having had complete spinal cord injury can experience orgasms through the vagus nerve, which can go from the uterus and cervix to the brain.

[15][16] Vagus nerve stimulation (VNS) therapy via a neurostimulator implanted in the chest has been used to control seizures in epilepsy patients and has been approved for treating drug-resistant clinical depression.

[18] VNS may also be achieved by one of the vagal maneuvers: holding the breath for 20 to 60 seconds, dipping the face in cold water, coughing, humming or singing, or tensing the stomach muscles as if to bear down to have a bowel movement.

In a six-month open-label trial involving three medical centers in Australia, Mexico, and Norway, vagus nerve blocking helped 31 obese participants lose an average of nearly 15 percent of their excess weight.

[20] Vagotomy (cutting of the vagus nerve) is a now obsolete therapy that was performed for peptic ulcer disease and now superseded by oral medications, including H2 antagonists, proton pump inhibitors and antibiotics.

[21] The procedure curbs the feeling of hunger and is sometimes performed in conjunction with putting bands on patients' stomachs, resulting in an average of 43% of excess weight loss at six months with diet and exercise.

[24] Or giving further evidence to the theory that dysregulated environmental stimuli, such as that received by the vagus nerve from the gut, may have a negative effect on the dopamine reward system of the substantia nigra, thereby causing Parkinson's disease.

[25] The sympathetic and parasympathetic components of the autonomic nervous system (ANS) control and regulate the function of various organs, glands, and involuntary muscles throughout the body (e.g., vocalization, swallowing, heart rate, respiration, gastric secretion, and intestinal motility).

Arnold's nerve ear-cough reflex, though uncommon, is a manifestation of a vagal sensory neuropathy and this is the cause of a refractory chronic cough that can be treated with gabapentin.

Although a large proportion of these are the result of idiopathic vocal cord palsy but tumours especially lung cancers are next common cause.