If you want to know what the vagus nerve is and what are the manifestations of increased stimulation of this nerve, we recommend that you read the following article. You will read more about increasing the irritability of the vagus nerve.
When the vagus nerve is overstimulated, in short, a series of processes and reactions occur in the body, for example, the arteries of the body dilate. Also, the heart rate decreases spontaneously and the heart’s contractile power decreases. Due to the above processes, the amount of oxygen uptake in the brain also decreases. Following this set, a person who is overstimulated by the vagus nerve will feel confused.
What is the vagus nerve?
Doctors say that the longest nerve pair in the brain that extends from the brainstem to the abdominal organs is the tenth pair of cranial or vagus nerves, with a total of twelve pairs of nerves coming out of both sides of the skull, with the vagus nerve being the tenth pair. Most people will not notice the function of their right and left vagus nerves, which are part of the autonomic nervous system.
But when you notice nerve function when nerve activity has stopped or increased due to injury or disease, the vagus nerve is one of the most vital nerves that keeps the body functioning normally. If the vagus nerve does not work normally, we will not be able to speak, breathe, eat, and our heart will move and beat very irregularly.
A wide range of messages must travel from the brain to the internal organs. These messages are transmitted from the brain to the organs via the vagus nerve. Conversely, sensory messages are received from these organs and travel to the brain. These messages are responsible for your body’s involuntary response.
The vagus is said to be derived from the Latin word meaning to wander. In other words, a precise description of this nerve can be found in its name because this nerve protrudes from the back of the skull, travels a long way in the neck, chest and abdomen, and its many branches reach the lungs, heart, larynx, stomach and corners. This nerve is sometimes called the pneumogastric nerve because, as we said, it innervates the stomach and lungs.
The vagus nerve carries information received from the organs to the brain and provides the necessary information about what the body needs to do, and ultimately transmits information that will be a group of neural reflex responses.
Sensory information is said to enter this nerve from the outer ear and the ear canal, throat, and upper larynx. The long branches of the vagus nerve travel to the organs inside the chest and abdomen, and are responsible for innervating the lungs, heart, gastrointestinal tract, esophagus, and part of the large intestine. The messages received from these nerve fibers will cause nerve reflexes.
Most of these reflexes originate in the brainstem. These are reactions and responses of the autonomic nervous system that manifest as motor responses and reflexes. For example, if irritants are present in the airways and stimulate the sensory nerve endings of the vagus nerve, you will experience a cough reflex. Also, the amount of air in the lungs can change the pattern of breathing that is commanded by the brainstem, the dilation of the stomach leads to nerve reflections that cause the wall to relax.
What are the functions of the vagus nerve?
Numerous tasks such as:
- Adjust heart rate
- Adjust gastrointestinal movements
- Adjusting the muscular movements of the mouth, including talking and keeping the larynx open while breathing
The vagus nerve sends afferent fibers to the external ear canal and part of the lining of the brain or meninges, which is why you may cough if you manipulate the inside of the ear, such as using a cleanser to clean your ear canal. In short, it provides innervation to all internal organs from the neck to the large intestine, except for the adrenal glands. The vagus nerve also innervates several skeletal muscles due to its important branching, including the laryngeal muscles.
Increased vagal irritability
The most important part of the autonomic nervous system is the parasympathetic part. The parasympathetic part works against the sympathetic part. The effects of the two parts will be opposite. If the sympathetic system is stimulated, it speeds up the heartbeat, while stimulating the parasympathetic nervous system, or in other words, overstimulation of the vagus nerve, will reduce the heart rate.
If the nerve is stimulated, the heart rate decreases. As the nerve is stimulated or the vagus nerve becomes overstimulated, the heart rate and heart activity may be slowed to such an extent that the person experiences cardiac arrest.
It is said that in 1921, a person named Otto Levy shows that in a laboratory frog, the stimulation of the vagus nerve releases a substance, which can reduce the heart rate of another frog that was only connected to the first frog through fluid transfer, and this unknown factor is called Vagusstoff.
It is now known what this substance is. The vagus nerve terminals release a chemical mediator called acetylcholine at the site of the heartbeat node in the right atrium. Acetylcholine slows the heart rate. We all have this constant heart rate regulation so that the sympathetic nervous system’s effect on the heart is balanced.
Vagus nerve fibers in the lungs:
The smooth muscles of the airways are also stimulated by the vagus nerve, so the irritability of the vagus nerve increases resistance to airflow or airway contraction.
The vagus nerve fibers, if stimulated, stimulate the smooth muscles of the stomach and intestinal wall to move more.
However, overstimulation of the vagus nerve affects the sphincter valve of the gastric outlet and relaxes it. Nerve fibers also stimulate the secretion of gastric acid and digestive enzymes that are released from the intestinal and gastric walls. Also, bile outflow from the gallbladder is increased by stimulating the vagus nerve.
What are the side effects of severe vagal nerve stimulation?
The most common side effects of vagal nerve stimulation in VNS include hoarseness, coughing, tingling in the neck, and swallowing problems. These only occur when the VNS is in operation. These side effects that are usually not severe, are controlled, and will improve over time relative to the patient’s tolerance.
Also, if the nerve is over-stimulated and stays stimulated for a long time, the following factors occur:
- Decreased heart rate
- Bradycardia and even cardiac arrest
- Low blood pressure
These factors, (bradycardia and hypertension) occur simultaneously.
Vagus hyperstimulation may be due to inflammatory diseases such as acute viral inflammation of the gastrointestinal tract or acute gallbladder inflammation, or in response to stimuli such as Carotid sinus massage, resulting in shortness of breath and straining. Also severe pain, for example, following blood sampling or injection of Botox or gel in rejuvenation.
If the irritation of the nerve is too severe, especially if the person is dehydrated, he will faint. A condition in which a person is dehydrated, causing the effects of vagal nerve stimulation to become more pronounced and causing the person to faint, is called vasovagal syncope.
In cases where a person has severe emotional arousal and extreme anxiety, the sympathetic nervous system becomes highly active. In these cases, the parasympathetic nervous system is sometimes activated compensatory to modulate the sympathetic nerve activity. This parasympathetic compensatory activation is accompanied by increased vagal nerve stimulation, causes a sudden drop in blood pressure and impaired speed and heart rate, and can lead to fainting.
Perhaps one of the reasons that a person faints in the face of extreme stress and emotional arousal is the above process. Also, due to excessive stimulation of the vagus nerve in this condition, the person may temporarily lose control of his urine in the moment of fear.
But doctors benefit from selective stimulation of the vagus nerve. This selective stimulation is used as a treatment that seems to be very useful for people with depression, and sometimes vagal nerve stimulation is also used to treat seizures.
What is VNS?
Vagus nerve stimulation or VNS is a technique for treating seizures and is a semi-invasive measure to control seizures. It is said that this process may be associated with improved seizure control in the long run, making seizure treatment shorter and more efficient, and reducing the need for medication. Also, due to this stimulation, some people may get rid of seizures completely.
How is VNS done?
The patient is placed under general anesthesia. The stimulus, which is the size of a coin, is placed under the skin in the upper part of the chest. A wire is removed from the device and travels under the skin to reach the vagus nerve and attach an electrode to the nerve. The vagus nerve will be accessed by making a small incision, usually in the neck. After the implantation of the device, the device sends electrical pulses at a certain distance by a computer according to the patient’s tolerance. Usually every five minutes a person is exposed to thirty seconds of electrical stimulation. The settings of this device will definitely be changeable.
When is VNS used?
Brain cells communicate with each other by sending electrical signals. When a person has a seizure, these patterns are disrupted, causing an uncontrolled electrical current in the brain cells.
These stimuli are due to the large amount of electrical stimulation in the brain that causes seizures. Most patients with seizures can control their seizures with medication. Thirty percent of patients do not recover from medication, and surgery may be performed to remove parts of the brain that have abnormal waves.
In patients who are not able to tolerate the side effects of drugs, they may go to the doctor for surgery, but in people for whom surgery is not possible for any reason and seizures with uncontrolled medication, VNS is a good treatment option.
What are the benefits of VNS?
VNS is not a definitive treatment and will not completely eliminate seizures. Therefore, reducing the number of seizures by more than fifty percent and reducing the severity of seizures and reducing the need for medication in the person, which improves the quality of life.