Vagus Nerve Definition

Combined sensory and motor neurons comprise the vagus nerve, which is responsible for immune response, heart rate, digestion, and mood control. The tenth cranial nerve (CN X) extends from the brain towards the abdomen, innervating the face, neck, and thorax as a motor, special sensory, and sensory neuron.

Vagus Nerve Function

The sensory, special sensory, motor, and parasympathetic functions of the vagus nerve are divided into four categories based on the kind of nerve fibre. The vagus nerve is mostly an afferent nerve that conveys sensory signals from the muscle to the brain, but it is also an efferent (motor) nerve that delivers signals from the brain to muscles. The parasympathetic nervous system regulates smooth muscular control. The vagus nerve begins in the brainstem’s medulla oblongata.

The medulla oblongata has four distinct vagal pathways:

• The dorsal nucleus is a part of the brain that provides parasympathetic signals to the viscera. 
• The solitary nucleus processes sensory information involving the tongue (taste) as well as visceral organs. 
• The trigeminal nucleus of the spine receives sensory information from the laryngeal mucosa and the outer ear. 
• The motor nerve connected with speaking, swallowing, and heart muscle movement is known as the ambiguous nucleus.

Cranial nerve nuclei constitute clumps of grey matter in the brainstem that serve as synaptic sites. Neurons entering via vagus nerve throughout the medulla oblongata synapse in their associated nuclei before to proceeding to other parts of the human body; likewise, signals transmitted towards the brain from other regions of the body synapse in their associated nuclei prior to reaching the medulla oblongata.

The external ear, throat (laryngopharynx), and voice box consist of skin and mucous membranes and are all innervated by CN X as a sensory nerve (larynx). It also gives visceral feelings. This leads the heart and visceral organs to feel discomfort, distension, vibration, and nausea. In response to chemical inputs such as neurotransmitters as well as hormones, the nerve also emits involuntary impulses. The heart, lungs, liver, pancreas, and intestines are among the visceral organs.

Having a particular sensory nerve, the vagus nerve collects data from the taste buds on the back of the tongue and the upper epiglottis (here special refers to smell, sight, taste, hearing, and proprioception). The muscles of the neck are innervated by CN X, which is a motor neuron.

While the sympathetic fight-or-flight response is not always necessary to survive, the parasympathetic nervous system automatically restores the body to a more relaxed state. The vagus nerve, which is a component of the parasympathetic nervous system, innervates the heart’s smooth muscle, the trachea, the bronchi of the lungs, and also the gastrointestinal tract. It will reduce the heart rate and breathing rate, as well as promote gastrointestinal peristalsis, if triggered.

Vagus Nerve Stimulation

Stimulation of the vagus nerve is not a new notion; vagal techniques have been used to reduce heart rate and promote calm for ages. The carotid artery was known as the “place of sleep” by the ancient Greeks because signals to this region activate the vagus nerve. It parallels the much more obvious and felt artery. The right carotid area is massaged to reduce heart rate and blood pressure. Every physician, according to Hippocrates, should be exceedingly skilled in the technique of “rubbing.”

In today’s medical world, there are two ways to activate the vagus nerve. The first are the vagal movements, which are a set of activities. The vagus nerve gets electrically stimulated in the second procedure.

Supraventricular tachycardia is a cardiac rhythm problem characterised by a fast heart rate that occurs unexpectedly. Symptoms include palpitations, shortness of breath, lightheadedness, and sweating. During the first therapy, patients are taught various vagal motions, which may often obviate the necessity for hospitalisation. These actions include coughing, retaining one’s breath, and spraying one’s face with icy water.

Such exercises raise intrathoracic pressure and, as a result, blood pressure for a short period of time. The vagus nerve reacts to this artificially increased blood pressure by trying to slow the heart, which is a parasympathetic signal which also reduces blood pressure. The diving response, which causes a decreased heart rate, a brief pause in breathing, and the tightening of peripheral blood vessels and increases oxygen delivery to the far more essential organs, is similarly activated by ice water on the face.

Other options are also viable. The gag response is elicited when the back of the throat is touched, which also activates the vagus nerve. Only those without atherosclerosis get carotid stimulation directly beneath the angle of the jaw, since plaque fragments may cause a stroke. Carotid massage stimulates the cranial nerve X by applying direct pressure. Only a medical expert should do this procedure.

Electrical vagus nerve stimulation (VNS) is a treatment that employs electrical impulses to stimulate the nerve. It may be administered using implanted equipment or as a removable, transitory treatment. Although not all medical journal articles concur that electrical vagal activation is advantageous, numerous physicians and patients have also reported positive changes in depressive episodes, multiple sclerosis, epilepsy, Alzheimer’s disease, metabolic syndrome, cardiovascular disorders, Parkinson’s disease, migraine, tinnitus (ringing in the ears), and cluster headaches during and after VNS. New wireless devices are now being created to assist in the rehabilitation of stroke victims.

According to recent research, transcutaneous vagus nerve stimulation (tVNS) in the outer ear over fifteen minutes per day enhanced cardiovascular health, happiness, and rest in those aged 55 and older. However, stimulating the ear to induce parasympathetic effects is not a novel concept. For generations, professional Chinese ear-pickers have used pressure, tuning forks, and ear-tickling procedures to perfect a peaceful national pastime that is fading away.

Vagus Nerve Damage

Due to the fact that the vagus nerve is a long nerve which branches out to different parts of the body, It may cause a variety of symptoms. The Latin term ‘vagus’ indicates’ wandering, ‘therefore this name describes the many routes of the vagus nerve.

Injuries to the cranial segment of the vagus nerve may be caused by head trauma, infection (encephalitis), ageing conditions, or continuous inflammation. The major function of the vagus nerve in the brain is to convey sensory innervation towards the skin of the back of the outer ear and also the membranes of the ear canal. Tinnitus and other hearing issues are not the result of CN X, although they do tend to improve when the nerve is activated. Due to their proximity to the vagus nerve, sinus infections and dental treatments may cause ear discomfort.

Pain referred from delayed throat cancer, for instance, may cause ear discomfort due to nerve injury farther down the body. Lyme neuroborreliosis and tick-borne encephalitis are caused by tick bites. Tick bites damage the peripheral nerves, including the cranial nerves, and may cause acute or chronic forms of brain infection in a small number of patients.

Trauma to the segment of this nerve that travels through the neck, such as during surgery, might cause it to be injured. It traverses the internal jugular vein and the carotid artery before dividing into the right and left coronary arteries shortly before the aortic arch, making it fairly visible. The vagus nerve serves both sensory and motor functions in the neck area between its outflow from the skull and this right-left divide.

If CN X is damaged, it might cause a weakened gag reflex, hoarseness or loss of voice, difficulty with articulation and speech, poor swallowing, and – as previously indicated – referred ear discomfort.

Vagus nerve injury may also be caused by chronic inflammation, degeneration, or autoimmunity. Longer parts of the stomach are generally affected, resulting in indications like reduced gastric acid secretion, irregular heartbeat and hypertension, vomiting and nausea, abdominal pain, and delayed gastric emptying (gastroparesis).

Vagus Nerve Disorders

Vagus nerve problems are mainly caused by lesions or illness, and vagus nerve conditions are significantly less prevalent. Tests for vagal injury vary from measuring the swallowing reflex to using computed tomography (a CT scan) to look at stomach emptying. An endocrinologist could examine glandular dysfunction linked to vagus nerve injury more carefully, and an ear, nose, and throat specialist might search for infections or tumours.

Nerve illnesses may be inherited or autoimmune in nature. Nerves degrade with time as well, particularly when combined with a poor diet and harmful lifestyle behaviours like smoking and heavy alcohol use. A shortage of blood flow may harm any of the cranial nerves, much like the rest of the body. Abnormalities of the vagus nerve are associated with metabolic disorders such as diabetes and autoimmune disorders such as multiple sclerosis; viruses and bacteria may also kill nerve tissue.

Recently, it has been suggested that viral diseases of the tenth cranial nerve are to blame for conditions such as chronic fatigue syndrome, post-traumatic stress disorder, as well as focus deficit hyperactivity disorder; nevertheless, there are numerous hypotheses circulating on the Internet, and scientific proof suggests that there is no single factor.

References

• Kenny B J, Bordoni B. (Updated 2019).  “Neuroanatomy, Cranial Nerve 10 (Vagus Nerve)”. Treasure Island (FL): StatPearls Publishing. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK537171/
• Langmore S E. (2001) “Endoscopic Evaluation and Treatment of Swallowing Disorders”. New York, Thieme Medical Publishers.
• Bretherton B, Atkinson L, et al. (July 2019) “Effects of Transcutaneous Vagus Nerve Stimulation in Individuals Aged 55 Years or Above: Potential Benefits of Daily Stimulation.” Aging. DOI 10.18632/aging.102074