The vagus nerve, also known as the “wanderer,” is an amazing structure. It is the 10th cranial nerve emerging from the brainstem at the base of the skull, coursing down the neck, to connect with structures in the mouth and throat. Continuing into the chest and abdomen, it connects with organs and tissues like the heart, digestive tract, liver, kidneys, spleen, and adrenal glands to become the longest nerve in the body. The vagus nerve has direct influence on these and other body tissues; it forms a direct connection to the brain and impacts on the immune system, modulates inflammation and affects the intestinal wall integrity. Some estimate that the vagus nerve alone is 75% of the parasympathetic nervous system, PNS. Eighty percent of the vagus nerve conveys sensory information and 20% signals a response reaction.

It is important to note that the PNS is part of the autonomic nervous system, or ANS. The ANS regulates involuntary processes like heart rate, blood pressure, and digestion. There are three commonly recognized parts of the ANS, the parasympathetic, sympathetic, and enteric.

The sympathetic nervous system, SNS, is the fight-or-flight part of the ANS. This means it prepares the body to respond to an emergency or urgent situation. Heart rate goes up, blood flow increases to muscles and the brain, and digestion is slowed. If appropriate to the urgency, the gut will be emptied by vomiting or defecation. Digestion is not important in a fight-or-flight situation. With these body responses in mind, think about the impact that chronic stress can have when the SNS is continually activated. In contrast to the SNS, the PNS is the calming part of the ANS. It promotes digestion, relaxation, and acts as the balance to the SNS. The third part of the ANS is the enteric nervous system which has been referred to as the second brain. This is because, like the brain, it has an extensive network of nerves, over 100 million neurons, and uses the same chemicals and cells as the brain. It helps regulate the gut with and without input from the central nervous. One important function is that it alerts the brain when there are problems.

Even though the vagus nerve has been viewed as acting as the balance for the SNS, research is showing an interesting range of functions and influences that can have significant impacts on the quality of health. The vagus nerve is part of the two way communication between the brain, gut, and microbiota, or gut flora. It is able to sense the gut flora metabolites and send that information to the central nervous system and then generate a response based on that information. Interestingly, the vagus nerve is able to affect permeability of the intestinal wall and effect changes in the gut flora. The vagus nerve has functions that reduce and manage inflammation.

With these valuable functions in mind, it is important to consider what can go wrong with the vagus nerve and how does dysfunction affect quality of health. Stress is a common negative impact on vagus nerve PNS function. Chronic stress increases the SNS and reduces the function of the vagus nerve. Misalignment issues of the cranium and first vertebra of the neck can also potentially reduce vagus nerve function. There are also reports of inflammatory conditions affecting the vagus nerve contributing to reduced function.

While inflammation is an important part of health when in the proper amount, problems arise when inflammation is excessive. Increased SNS associated with chronic stress contributes to increased inflammation. The associated reduction in the PNS means that there is a lower ability to respond and control the level of inflammation. This situation has been associated with inflammatory bowel issues and other immune dysfunction diseases. Reduced vagus nerve function has also been associated with increased levels of anxiety and a lack of mental focus. Vagus nerve dysfunction in our pets can appear in a variety of ways including as chronic digestive disorders, immune imbalance, increased allergy related itching, difficulty with training and mental focus, and discomfort in the upper neck.

Evaluation for vagus nerve dysfunction can be a valuable part of managing these chronic disorders along with the other indicated treatments. Therapy for a vagus nerve issue depends on the cause of the problem and may include stress reduction and osteopathic manipulations of the neck.

If you have questions about the vagus nerve, contact your veterinarian.Ron Carsten, DVM, PhD, CVA, CCRT was one of the first veterinarians in Colorado to use the integrative approach, has lectured widely to veterinarians, and has been a pioneer in the therapeutic use of food concentrates to manage clinical problems. He is also the founder of Colorado Animal Rescue, CARE. In addition to his Doctor of Veterinary Medicine, he holds a PhD in Cell and Molecular Biology and is a Certified Veterinary Acupuncturist and Certified Canine Rehabilitation Therapist. He practices integrative veterinary medicine in Glenwood Springs. Dr. Carsten is the 2022 Colorado Veterinary Medical Association Distinguished Service Award recipient.