What is the function of the Vagus nerve?

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Neurology and Neurosurgery are one of the most complicated fields of medicine, as a minor damage to any nerve or tendon can create havoc in the mental functions of an individual. But today with  many non-invasive procedures and CT scans available to look inside the brain, surgeons are able to perform the most complex operations and save lives. Our brain consists of a complex network of nerves and tissues. The Cranial nerves emanate directly from the brain whereas the spinal nerves as the name states originate from the Spine. There are 12 pairs of cranial nerves which perform the sensory and motor functions in the body. Vagus Nerve is one such  cranial nerve that  also happens to be the longest nerves in the body that innervates the throat, thorax, abdominal muscles and other organs and has several functions, which is why it  is one of the most important parts of our nervous system.

What is Vagus Nerve?

It is known to be one of the longest of all the cranial nerves. The name Vagus Nerve, has originated from the Latin word, which means ‘wandering’. It gets this name because the nerve  wanders from the brain stem via various organs in the neck, thorax and abdomen. The vagus nerve is two nerves that go through the brain stem and enter different parts of the body such as the heart and the stomach. Vagus nerve leaves the brain stem from the rootlets present in the medulla that has been found to be caudal to the rootlets  in the  ninth carnial nerve. The vagus nerve comprises of two sensory ganglia which are segmented into superior and inferior vagal ganglia. Glosso-pharyngeal and Vagus Nerves together connect with many similar brain stem nuclei such as the nucleus ambiguous, dorsal motor nucleus of the vagus, nucleus solitarius and spinal nucleus and hence when one  gets damaged the other ones mostly get damaged as well.

The vagus nerve connects our brainstem to the body, due to which the brain receives, controls and monitor several body functions automatically. The vagus nerve forms a sort of electrical circuit while linking our heart, lungs, and gut to the brain-base. This type of ancient circuit connection is common in birds, mammals, reptiles and also amphibians. This vagus nerve connection resembles the USB or Firewire computer connection in many ways. It encompasses the major nervous system and contributes to motor control of physiological functions including gut mobility and heart rate. 

What are the Three major branches of  the Vagus Nerve?

The Vagus nerve is hooked to the throat, Heart, and outer ears. From the nucleus ambiguous come up three major branches which become a part of vagus nerve and exit the nerval distal towards the jugular foramen. The pharyngeal branch moves through the internal as well as the external carotid arteries and then enters the pharynx placed at the upper border inside the middle constrictor muscle. The pharyngeal branch supplies complete muscles of the pharynx as well as the soft palate excluding the tensor palati and stylopharyngeas. The muscles supplied by this branch consist of constrictor muscles known as levator veli palatini, salpingopharyngeus, and palatoglossal and palatopharyngeus muscles. The second branch is the superior laryngeal nerve branches which is placed distal to pharyngeal branch and lateral to pharynx. It further divides into internal as well as external branch. The internal branch is completely sensory while the external branch moves through the cricothyroid muscle which is supplied by the second superial laryngeal nerve branch. Recurrent branch is the third branch of the vagus nerve and it moves various paths both on the left as well as the right side of the body.

What are the Functions of  the Vagus nerve?

Some of the main functions of the Vagus Nerve include,

1. Breathing
2. Speech
3. Sweating
4. Helping in keeping the larynx open during breathing
5. Monitoring and regulating the heartbeat
6. Informing the brain of the food that is ingested and food that has been digested
7. The Vagus Nerve performs the major function of emptying the gastric region of food
8. Any damage to the vagus nerve causes, Gastroparesis which is losing the muscular function in the stomach and intestines. This results in food being emptied slowly, that leads to other problems such as fermentation of food  in the stomach and food getting compressed into hard pellets which can cause severe problems if the pellets get stuck in the intestine. Specially in people with diabetes, when sugar levels get high and are not well controlled, it can result in the vagus nerve damage. 

What are the Disorders of the Vagus Nerve?

The Vagus Nerve disorders also called the 10th Cranial nerve disorders can cause several problems to the body as it is a key player in relaying information to the brain. The disorder can affect anyone from birth to midlife to old age.

• It can cause problems in the digestion of food in the stomach as it helps in peristalsis of the stomach.  
• Vagus nerve disorders can occur when there is pressure on the vagus nerve or due to other stimulation. Sometimes people lose the vagus nerve in a cancer surgery.
• The individual with the disorder might experience nausea, lose consciousness and sweaty skin.
• Since it regulates the heart beat, the vagus nerve disorder can slow down the heart rate resulting in a drop in the blood pressure. 

What is Vagus Nerve Stimulation?

Vagus Nerve Stimulation (VNS) is used in preventing epileptic seizures.  A mild electric pulse is given to the patient's brain through the vagus nerve to prevent the seizures from repeating. In this treatment a very small device, also known as the "pacemaker of the brain" which is the size of a  silver dollar is used to send mild electrical impulses through the Vagus nerve. The patient is administered general anesthesia in this 90 minute long procedure. A small incision is made inside the neck just above the collarbone by the surgeons for this implantation. The device is battery operated, and has an electrical pulse generator. After it is implanted, electrodes with insulated plastic are run into the vagus nerve from under the skin on the neck’s left side. The pulse is set to operate alternately by turning on every few seconds(the time is set by the surgeon) and the turning off. The patient does not feel  the cycle of pulses nor the device operation. The VNS device lasts anywhere from 5-10 years. VNS helps people in controlling their seizures.

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