Introduction to the Vagus Nerve
The vagus nerve is the paired tenth cranial nerve that branches out from the brain and supplies parts of the gastrointestinal system such as the stomach, and parts of the respiratory system such as the lungs. To supply vital organs, it has further to travel than the other cranial nerves.
It is has branches located on both the left and right side of the body, and each branch will initially travel down to produce the auricular nerve. This branch supplies the external acoustic meatus or the ear canal. The branches also supply innervation to the pharynx. From here the right and left branches of the vagus nerve will enter the thorax to supply the organs located within the thorax and eventually down to the abdomen. This nerve will therefore innervate all the critical organs within this area except the adrenal gland, descending colon, rectum, and anus. Based on this it is possible to see the importance of this nerve in controlling the heart rate, digesting food, and regulating breathing. Thus there are quite a number of presentations in the symptoms of vagus nerve damage.
What Happens When The Vagus Nerve Is Damaged?
Since the vagus nerve is so important in the innervation of many organs, a large variety of symptoms of vagus nerve disorder can result. Starting from the muscles of the throat, damage to the vagus nerve can produce problems with the person’s voice as it supplies nerves to the vocal cords. The voice will sound strained, deep, and hoarse. There will be difficulty with swallowing and even a reduced gag reflex. Thus the person might choke during eating and drinking if they have vagus nerve damage. This can be really deadly if the laryngeal muscles are paralyzed.
As a result of the vagus nerve innervating the external ear canal and eardrum, sound waves are not properly interpreted and this can result in partial or full hearing loss. With vagus nerve innervation to organs inside of the thoracic cavity, damage to both branches of the vagus nerve will not cause a reduction in heart rate but an increase. There will also be an increase in blood pressure. This is because the vagus nerve provides parasympathetic support to the cardiovascular system.
The muscles of the esophagus will lose their tone and this can create a problem with food entering the esophagus if the vagus nerve is damaged. Inside the abdomen, there is an increase in the amount of acid produced in the stomach. This can result in vomiting and damage to the lining of the stomach. The intestines will lose their ability to carry out peristalsis to move the food along the digestive tract. Constipation or even more bowel impaction can result.
Other symptoms of vagus nerve disorder involve problems with the bladder leading to inability to hold in urine, a condition known as incontinence.
Print Source: Cotran R, Kumar V, and Robbins, SL. 1999. Robbins Pathologic Basis of Disease, 6th Ed. W.B. Saunders Company, Philadelphia.