The Vagus Nerve: Your Very Own Mind-Body Feedback Loop

I wrote about the importance of gut health and how it relates to the nervous system for Annmarie Skincare a few months ago, but I have been really wanting to expand that article to talk about vagus nerve and the enteric nervous system. It’s all very complex and micro-sized but in a nutshell, your body has a sort of a built in feedback system. It’s the vagus nerve and it touches every major organ in your body.

Researchers have found that up to 90 percent of the signals that this primary nerve sends is from the gut to the brain and 90 percent of the what the brain sends down the body it sends through the vagus nerve. This internal feedback is happening consistently throughout daily life so it’s no wonder that terms like ‘hangry’ and ‘gut instinct’ are such a real part of our lives.

Structure and function

The vagus nerve is a main part the body’s enteric nervous system and though it sounds like one nerve that winds through the body, it is actually a system of nerves that reach out and touch every major organ. The vagus nerve builds the connection between our physical health and our mental well-being by feeding information about the body through the body. It’s like an internal walk-talkie.

Though it touches every organ, researchers think that this special set of nerves exists specifically to function as an extensive digestive system feedback loop. The digestion system is how we fuel our body and it is the main place that we bring external things internally so it makes sense that we would evolve to have a direct line of communication between our stomach and our brain – before supermarkets and big agriculture, eating was a dangerous part of life and it took consistent communication of all of our senses to find safe nutrition (of course eating is still dangerous, but it’s much different now and we’re not doing a great job listening to our guts).

You can look at drawings here to get an idea of how intricately the vagus nerve is connected to our digestive organs (I recommend it, it’s pretty cool). Essentially the nerves start in the brain sort of right where your skull meets the back of your neck. From there, it branches almost immediately and moves into the jaw and around the larynx and pharynx to help the body figure out the right tube for food to enter. There’s another branch for the heart and then the nerves wrap around the esophagus and travel down to the surface of the stomach, which is coated with neurons that independently function as part of the enteric nervous system. It also has smaller branches that reach for the liver, pancreas, gall bladder, large and small intestines, and the spleen. Basically, if it’s part of the digestive system, the vagus nerve has an nerve on it and is reporting to the brain.

It’s important to note here that the vagus nerve (VN) and the enteric nervous system (ENS) are two separate parts of our body, but they are vastly connected. The ENS can continue to function even if the VN connection is severed, that is why the ENS is considered an additional nervous system in our body, but the communication between the stomach and the brain becomes much more difficult.

My first introduction to the vagus nerve, and still the best real-life example I have of how it works, was a couple of years ago when I interviewed a woman who suffers with gastroparesis. This is essentially an illness where the motility of the stomach is absent. Gastroparesis impairs normal digestion because the stomach is unable to breakdown or push food into the small intestine. This can be caused by a lot of things from diabetes to radiation to a neuromuscular disease that shuts down motor function within the smooth muscle.

In her case, she had been dealing with acid reflux for a long time and developed cancerous cells in her esophagus. She had surgery to remove those cells and the doctors accidentally burned a hole in her vagus nerve. She told me that when she ate, it felt like she was being shot in the stomach and sometimes the pain was so bad after she ate that she would pass out. She ended up at the mayo clinic and they found that the vagus nerve had been compromised. She spent a few months there where they helped to heal her ENS and allow her body to accept nutrients again but she still suffers from the occasional pain. She has to be very careful with her diet and she can’t push herself too hard in stressful situations but it didn’t stop her, she’s still Chasing the World.

Endocrine relations

The enteric nervous system is considered the “second brain” because modern science discovered the vagus nerve after it discovered the brain in our heads. In reality, the enteric nervous system most likely evolved as the first brain in animals that were stuck to a rock and waiting for food to come along. As life evolved, animals needed a more complex brain to be able to find a mate and travel to find food. Since eating is still extremely important and also dangerous, animals evolved to have a second brain, that brain is the central nervous system that we know now.

I basically said all that to say that it isn’t the least bit surprising that there are more neurotransmitters in the gut than the spinal cord, something like 100 million neurotransmitters are created and/or stored in the gut, including major transmitters like serotonin, dopamine, glutamate, adrenalin. It also contains endorphins, neuropeptides, and benzodiazepines. The brain in our head uses neurotransmitters and neuropeptides to communicate, endorphins to reduce our perception of pain, and benzodiazepine is created in the body to relieve anxiety. The vagus nerve, being the connection between the gut and the brain, is instrumental in communicating between the body’s brains to keep it healthy and happy.

About 50 percent of dopamine in the body exists in the gut. In the brain, it signals the feelings of pleasure and reward. In the gut it transmits messages between neurons to coordinate muscle contractions like that of the colon – who says pooping isn’t rewarding!

A study on Parkinson’s disease headed by Heiko Braak at the University of Frankfurt, Germany gives evidence that the proteins that destroy the dopamine receptors in the brain are also in concentration in the gut. In fact, there was so much of the dopamine-destroying protein in the gut that Braak’s study pointed to the gut being where the dis-ease actually starts and the vagus nerve transports those proteins to the brain. This study has lead to new schools of thought in the fields of alzheimer’s and autism, searching the gut for answers to what could be happening in the brain.

In addition to 50 percent of the dopamine, 95 percent of the serotonin in the body exists in the gut. Serotonin is our ‘feel good’ molecule. It is involved in helping us sleep, preventing depression, regulating appetite and body temperature. Serotonin produced in the gut goes into the bloodstream and helps to repair damage to the lungs and the liver. It’s also important for the development of the heart and regulating bone density by inhibiting formation.

Serotonin develops very early within the body to act as a growth factor to aid the development of the ENS. If stress is present in the early years of life, it can affect levels of serotonin in the gut and has been linked to the development of irritable bowel syndrome later in life. Thinking about all of these different functions of serotonin, the overuse of SSRIs (serotonin-specific reuptake inhibitors) in the treatment of dis-eases like depression and IBS make sense but increasing the amount of serotonin in the bloodstream often has unintended consequences and the side-effects of this type of drug can be devastating to the body.

Although serotonin and dopamine are only two of neurotransmitters found in the body, their presence is vital in the brain and in the gut. There are many more neurotransmitters that use the gut-brain axis to keep us in our good health and wellbeing. Our brain and our gut are in constant communication and that isn’t just something that’s really, really cool. Knowing that our brain and our stomach are so intricately connected will allow us to be more conscious about how the food we eat directly affects how good we feel and vice versa.

References:

http://emedicine.medscape.com/article/1875813-overview#a1
http://chriskresser.com/the-healthy-skeptic-podcast-episode-9/
http://patients.gi.org/topics/gastroparesis/
http://www.psyking.net/id36.htm
http://www.nytimes.com/1996/01/23/science/complex-and-hidden-brain-in-gut-makes-stomachaches-and-butterflies.html?pagewanted=all
http://www.holistichelp.net/blog/how-to-increase-gaba-and-balance-glutamate/

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