Vagus nerve

The vagus nerve (Latin. nervus vagus) or pneumogastric nerve is tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem (somewhere in the medulla oblongata) and extends, through the jugular foramen, all the way down past the head, right down to the abdomen. The vagus nerve is arguably the single most important nerve in the body.

The medieval Latin word vagus means literally "wandering" (the words vagrant, vagabond, and vague come from the same root). It is also called the pneumogastric nerve since it supplies both the lungs and the stomach.

Innervation
This nerve supplies motor and sensory parasympathetic fibers to virtually everything from the neck down to the first third of the transverse colon. In this capacity, it is involved in, among other things, such varied tasks as heart rate, gastrointestinal peristalsis, sweating and speech (via the recurrent laryngeal nerve).

The vagus also controls a few skeletal muscles, namely:


 * Levator veli palatini muscle
 * Salpingopharyngeus muscle
 * Palatoglossus muscle
 * Palatopharyngeus muscle
 * Superior, middle and inferior pharyngeal constrictors
 * Muscles of the larynx (speech).

This means that the vagus nerve is responsible for quite a few muscle movements in the mouth, and also is vitally important for speech and in keeping the larynx open for breathing.

It also receives some sensation from the outer ear, where there is the Auricular branch (also known as Alderman's nerve) and part of the meninges.

The vagus nerve and the heart
Parasympathetic innervation of the heart is mediated by the vagus nerve. The right vagus innervates the SA node. Parasympathetic hyperstimulation predisposes those affected to bradyarrhythmias. The left vagus when hyperstimulated predisposes the heart to AV blocks.

At this location Otto Loewi first proved that nerves secrete substances called neurotransmitters which have effects on receptors in target tissues. Loewi described the substance released by the vagus nerve as vagusstoff, which was later found to be acetylcholine.

The vagus nerve has three associated nuclei, the dorsal motor nucleus, the nucleus ambiguus and the solitary nucleus.

VNS therapy
Vagus nerve stimulation therapy using a pacemaker-like device implanted in the chest is a treatment used since 1997 to control seizures in epilepsy patients and has recently been approved for treating drug-resistant cases of clinical depression. Mild degree of intermittent VNS by daily performance of certain breathing exercises (Pranayama) over a period of several weeks lowers blood pressure and the heart rate in persons with elevated blood pressure and/or elevated heart rate, and may also stabilize mood and affect.