Vagus Nerve Function: Your Body’s Master Regulator

The vagus nerve, or the ‘wandering nerve,’ is the tenth cranial nerve (X). It originates in the medulla oblongata, the lower part of the brainstem, and travels down through the neck and spine. From there, it branches out to connect with vital organs throughout the body.

Vagus nerve branches influence most vital functions and act as communication bridges between the brain and the organs, ensuring the body maintains balance, calm, and resilience despite environmental challenges. But how exactly does the vagus nerve function?

In this article, you will find an in-depth explanation of the vagus nerve function, what happens if it is not working correctly, and ways to promote relaxation.

The autonomic balance: sympathetic vs. parasympathetic function

The autonomic nervous system (ANS) regulates involuntary physiological responses such as heart rate, blood pressure, respiration rate, and digestion. The ANS is divided into the sympathetic (fight or flight) and parasympathetic (rest and digest) nervous systems. Think of them like the gas and brake pedals. Both have opposite yet complementary and essential roles.

The vagus nerve is the cornerstone of the parasympathetic system, responsible for about 75% of the drive. Efferent (motor) fibers carry information from the central nervous system (CNS) to the organs, while afferent (sensory) fibers carry feedback information from the organs back to the CNS.

This creates a feedback loop that enables the vagus nerve to adjust bodily functions, such as heart and breathing rates, in response to environmental challenges. This helps to maintain balance once the perceived threat or exercise is over. Each branch is responsible for different organs, but they all work in unison.

Here is a quick overview of the two arms of the ANS:

I hope this side-by-side comparison helps you understand how the vagus nerve maintains equilibrium and contributes to stress resilience and overall health.

Core functions of the vagus nerve

The vagus nerve's main role is to help the body respond and adapt to the environment by sending signals back and forth between the organs and the central nervous system. To explain in more detail, we have to look at the anatomy and physiology of each system. I will only focus on the more complicated and systemic processes, oversimplified in the table above.

Cardiovascular regulation

Signals from the sympathetic and parasympathetic nervous systems carefully regulate heart rate, rhythm, strength of contraction, and blood pressure. As previously mentioned, the vagus nerve is responsible for the parasympathetic side. It sends electrical impulses from the brain to the heart and sensory feedback back to the brain, continuously from heartbeat to heartbeat.

Hence, this nerve is essential for maintaining balance in the cardiovascular system.

Baroreceptor reflex

Baroreceptors in the aortic arch are specialized to sense changes in arterial pressure and connect to the brain via the vagus nerve. When blood pressure increases, the baroreceptors stretch. This stretch triggers increased signaling, to which the brain responds by decreasing sympathetic and increasing parasympathetic signaling. Increased vagus nerve activity slows the heart rate, reduces how much blood the heart pumps, and causes blood vessels to widen. The combined result is reduced blood pressure, which brings it down to normal values.

In the opposite scenario, when blood pressure decreases, baroreceptors are less stretched and send fewer signals or none at all. This leads to a decrease in vagal activity and an increase in sympathetic signaling.

This reflex works beat-to-beat to maintain blood pressure and heart rate within the normal range despite environmental challenges. Returning to our car analogy, this is like driving in traffic. You constantly watch what is happening around you and make minor, quick adjustments to the gas and brake pedals to stay in control. In the same way, the body produces tiny, ongoing changes to remain balanced.

Bainbridge reflex

Bainbridge, also known as the atrial reflex, monitors the return of blood to the heart and helps respond accordingly. Low-pressure stretch receptors detect increased pressure in the atria due to extra blood volume and send signals to the brain via the vagus nerve. In response, the brain reduces vagus nerve activity and increases sympathetic signaling, which increases the heart rate.

It is somewhat similar to your windshield wipers speeding up when the rain gets heavier. They adjust automatically to keep up with the increased flow, just as your heart does unless there are problems in any part of the system.

Respiratory regulation

The vagus nerve also plays an important role in regulating breathing by connecting the lungs and airways to the brain.

First, the sensory fibers send continuous updates and feedback from the lungs to the central nervous system. This lets the brain monitor the respiratory system and make any required adjustments.

Second, as you probably have experienced, during exercise or a stressful situation, your breathing becomes more shallow and rapid — this is driven by the sympathetic nervous system. Once the stress or strenuous activity is over, the vagus nerve helps shift things back into a more relaxed state. Its motor fibers mildly constrict the airways to take deeper breaths, returning the respiratory rate to normal.

Interestingly, this can also work in reverse, where deeper breaths may promote vagus nerve activity and help the body relax. I like to incorporate deep breathing exercises after my workouts to let my body know that the intense part is done and to promote recovery and relaxation.

Digestive system control

The parasympathetic nervous system stimulates digestion, hence the name ‘rest and digest.’

The vagus nerve communicates continuously with the digestive system through steady (tonic) signaling. These signals control the release of gastric juices and gut movements when needed. Other cranial nerves detect the sight, smell, and taste of food and send this information to the brain. In response, the brain activates the vagus nerve, which sends signals to the stomach. The release of the neurotransmitter acetylcholine onto the stomach lining activates parietal cells to secrete acid and chief cells to release pepsinogen, an inactive form of the enzyme pepsin, which breaks down protein.

The vagus nerve also sends feedback back to the brain. For example, if the stomach contents are not acidic enough, signals are sent via the vagus nerve to increase acid secretion and fine-tune enzyme release.

Furthermore, the vagus nerve also coordinates digestive movements, especially in the upper tract: the lower esophagus and the stomach. Vagal signals trigger smooth muscle to move food along. They also stimulate the release of relaxing factors like vasoactive intestinal polypeptide (VIP) or nitric oxide. These compounds relax parts of the digestive tract to help time the contractions.

As digestion moves down the tract, the vagus nerve’s role decreases, and the enteric nervous system (ENS) takes over. ENS is sometimes called the second brain, and it refers to the complex neural network in the gut that can function independently from the brain but is in close communication via the vagus nerve.

Besides its role in the digestive tract, the vagus nerve is also critical in linking the brain and the gut — the gut-brain axis. This connection goes beyond physiological function and may influence mental well-being, mood regulation, cognition, and various disorders. Despite more studies on the gut-brain axis and its influences, the science behind ‘gut feelings’ is still inconclusive.

Immunoregulation

The vagus nerve also controls inflammation through the inflammatory reflex. This reflex regulates the innate immune response to infection or injury.

Vagal sensory fibers detect signals from the immune system, such as inflammatory molecules or pathogen products. This information is then sent to the brain, which processes the body's immune status and sends signals back via the vagus nerve. This results in a suppressed release of pro-inflammatory cytokines — key drivers of inflammation.

If this reflex is disrupted, the immune system may become overactive, resulting in excessive inflammation and even cytokine toxicity. On the other hand, boosting this pathway via vagus nerve stimulation or with chemical compounds is being studied as a potential treatment for autoimmune conditions, obesity-related inflammation, and insulin resistance in animals. However, such methods require further research and human clinical trials before being used in a clinical setting.

Understanding and measuring vagal tone

Vagal tone is a scientific term that describes how effectively the vagus nerve maintains and restores parasympathetic activity after stress. It reflects both the strength and the adaptability of vagus nerve signaling.

During high-stress situations, the sympathetic nervous system takes over: heart rate increases, breathing quickens, digestion slows, and basically, your body prepares to fight or to run. After the ‘danger’ ends, the vagus nerve signaling brings the body back to a calm and balanced state. The quicker and more efficiently this happens, the higher the vagal tone. High vagal tone is associated with better health and resilience.

On the other hand, low vagal tone means slower recovery from stress. People with low vagal tone may get stressed more easily and stay in fight-or-flight mode for longer. This may contribute to anxiety, poor digestion, bloating, increased inflammation, or a persistently elevated heart rate.

When vagus nerve function is disrupted: symptoms and conditions

Vagus nerve dysfunction is not an official medical diagnosis. There is a lack of scientific consensus on whether certain symptoms derive from vagus nerve function or other physiological changes. However, some believe that impaired vagus nerve function can cause:

• Impaired heart rate control
• Digestive issues
• Poor resilience to stress

That being said, vagus nerve dysfunction has been trending on social media, with creators attributing everything under the sun to vagus nerve and parasympathetic dysfunction.

However, just because you are experiencing an issue with something that is under vagal control, it does not automatically mean your vagus nerve is impaired. Furthermore, despite the vagus nerve's critical role in numerous physiological functions, it is always a part of the puzzle in intricately connected neural systems and physiological processes.

Supporting healthy vagus nerve function: practical approaches

Several strategies have become popular in social media as a way to improve your vagus nerve function:

• Breathing techniques
• Meditation and mindfulness practices
• Physical activity
• Brief cold exposure techniques
• Social connection and positive interactions

As you may have noticed, these techniques align with general health advice and ways to manage stress. While they may increase vagal nerve function by promoting relaxation, there is a lack of research on their effectiveness. I would suggest aiming to manage stress, working out regularly, eating well, and not forgetting to socialize, rest, and have some fun rather than self-diagnosing vagus nerve dysfunction on TikTok and looking for ways to reverse it.

Medical interventions: vagus nerve stimulation

Vagus nerve stimulation (VNS) is also possible through specialized devices that target the left vagus nerve.

Invasive VNS (iVNS) involves surgical implantation of the device and has been approved by the FDA for drug-resistant epilepsy and treatment-resistant depression. Due to surgery-associated risks, this approach is like a last resort for treatment.

Transcutaneous VNS (tVNS) devices are also available. They are noninvasive and use attachable electrodes on the neck or ear. Despite at-home tVNS devices gaining popularity, these are regarded more as general wellness devices and currently have no defined guidelines on the most effective location, frequency, current intensity, or duration to achieve therapeutic effects. If you want to learn more about the science behind VNS, you may want to check my other article on the vagus nerve.

Final word: embracing vagus nerve health for overall well-being

The vagus nerve is a major regulator of bodily functions, responsible for maintaining homeostasis in response to environmental challenges. It regulates most organ systems and facilitates communication between the brain and the target organs. It is also believed to have a role in mental health through the gut-brain axis, but more research is needed.

Most people do not need to concern themselves with ways to improve vagal nerve function, and vagus nerve dysfunction is not an official medical diagnosis. However, incorporating stress-management practices like breathing exercises and meditation would benefit most. If you have nerve damage, it will manifest as serious symptoms requiring medical attention, and you will be given treatment and guidance on it.

Surgical implantation of vagus nerve stimulators has been approved for treatment-resistant epilepsy and depression but carries surgery-associated risks. Topical devices are also available, but their benefits are less defined due to differences in design and protocols.