The vagus nerve (also called pneumogastric nerve or cranial nerve X) is the tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem (within the medulla oblongata) and extends, through the jugular foramen, down below the head, 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 innervates both the lungs and the stomach.

Innervation

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The vagus nerve supplies sensory parasympathetic fibers to all the organs except the suprarenal glands, from the neck down to the second segment of the transverse colon. 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 such varied tasks as heart rate, gastrointestinal peristalsis, sweating, and quite a few muscle movements in the mouth, including speech (via the recurrent laryngeal nerve) and keeping the larynx open for breathing. It also receives some sensation from the outer ear, via the Auricular branch (also known as Alderman's nerve) and part of the meninges.

The vagus nerve and the heart

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Parasympathetic innervation of the heart is mediated by the vagus nerve. The right vagus innervates the Sinoatrial node. Parasympathetic hyperstimulation predisposes those affected to bradyarrhythmias. The left vagus when hyperstimulated predisposes the heart to Atrioventricular (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.

Drugs that inhibit the muscarinic cholinergic receptor (anticholinergics) such as atropine and scopolamine are called vagolytic because they inhibit the action of the vagus nerve on the heart, gastrointestinal tract and other organs. Anticholinergic drugs increase heart rate and are used to treat bradycardia(slow heart rate) and asytole which is when the heart stops contracting. Anticholinergic drugs relax the detrussor muscle and cause constipation which again involves the vagus nerve.

Bulemics and anorexics have high vagal activity which is associated with the arrythmias seen in these patients.

VNS therapy

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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.

The valsalva maneuver may activate the vagus nerve.

Physical/emotional effects

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Symptoms of nervousness, especially in a social context, such as increased heart rate/palpitation, impediment or inability to speak, stomach irritation, and excessive perspiration are caused in part by the vagus nerve.

An effective method of curbing these symptoms is by taking a deep breath, and forcefully blowing out through a small hole in your mouth, letting your cheeks puff out. This puts pressure on the nerve, and tells it to reset.

Excessive activation of the vagal nerve during emotional stress, which is a parasympathetic overcompensation of a strong sympathetic nervous system response associated with stress, can cause vasovagal syncope because of a sudden drop in blood pressure and heart rate. Vasovagal syncope affects young children and women more often. It can also lead to temporary loss of bladder control under moments of extreme fear.

External links

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• Anatomy of the vagus (Loyola medical school)
• Overview at yale.edu
• Review article on vagus nerve stimulation for treatment of depression

Peripheral nervous system | Autonomic nervous system | Cranial nerves | Thorax | Abdomen

العصب التائه | Nervi vague | Nervus vagus | Nervio vago | Vago | Nerf vague | Nervo vago | Klajoklinis nervas | Nervus vagus | Nervus vagus | 迷走神経 | Nerw błędny | Nervo vago | Kiertäjähermo