From Brain to Bowels-The Vagus Nerve_Final

>> Hi. Here's a question for you. Can you name the nerve that connects the brain to the gut and many other important organs? Here's a hint. It's the longest nerve in the autonomic nervous system. If you said the vagus nerve, you are correct. This cranial nerve extends all the way from the brain to the intestines. Along the way, it branches out making connections with many of the major organs in the chest and abdomen. You can think of it like a tree with a network of branches that extend out from its trunk. The vagus nerve is sometimes referred to as the wandering nerve. It shares the same Latin root as vagabond and wanderer. It got this nickname for the way it wanders all the way from the brainstem down to the visceral organs extending out along the way. The vagus nerve is like the captain of your nervous system. It starts in the brain and passes through the throat, esophagus, lungs, heart, diaphragm, and intestines. It has a role to play with all of these organs, helping them communicate with one another and carry out important functions. Specifically, the vagus nerve is intimately involved with carrying out functions of the parasympathetic nervous system. Recall that this is the part of the nervous system that regulates rest and digest. So as you can imagine, it has an important role to play in relation to digestive health. Let's take a look at some of the ways that it does this. The vagus nerve is an important information highway from the brain to the gut and back again. Think back to the gut-brain connection. This highway communicates taste and feelings, and it's along this nerve that the gut sends signals to the brain, what we know as our gut instincts. It's the link between our microbiome and our emotions. In addition to our gut instincts, this highway carries lots of different signals from the gut to the brain and vice versa in the form of neurotransmitters. The most important ones in the gut are acetylcholine an excitatory neurotransmitter and GABA an inhibitory neurotransmitter. So how does this work in the gut? Well, acetylcholine excites or activates the nervous in the gut to start digesting by activating the parasympathetic nervous system. This causes the intestines to start moving and digesting. It also turns off the sympathetic responses, slowing down the heart rate and increasing blood flow to the gut. The instruction to release this neurotransmitter comes from up above, the brain. GABA is an inhibitory neurotransmitter, which means it inhibits the sympathetic response in the brain and modulates gut motility and secretion. A healthy vagus nerve also helps regulate inflammation. The vagus nerve can stimulate the parasympathetic nervous system and activate what's known as an inflammatory reflex. When the vagus nerve sees certain stress hormones like cortisol, it talks to the immune system in the gut instructing it to release histamine which will cause an inflammatory reaction. This inflammation prepares the gut for potential pathogens. The body does this because it knows the immune system is suppressed in times of stress. Inflammation is the secondary line of defense. Therefore, when the stress is over and the immune system returns to normal, the body no longer needs to respond with inflammation. As long as the immune system doesn't detect any pathogens or infection, the brain will then send a signal to the gut with GABA, our main inhibitory neurotransmitter, decreasing the release of proinflammatory cytokines and inflammation. And acetylcholine will be released to stimulate parasympathetic activities. All this communication occurs via the vagus nerve. Unless a true infection exists that needs to be addressed, it is important that the vagus nerve releases neurotransmitters that trigger an anti-inflammatory response. Without it, inflammation can become chronic. Chronic inflammation is associated with conditions like inflammatory bowel disease where the gut lining is chronically inflamed. Studies have found that when the vagus nerve is cut, symptoms of gut conditions increase, thus poor vagal tone may play a role in these conditions. But let's back off for just a second. Vagal tone? Vagal tone refers to the activity of an individual's vagus nerve. The best way of assessing vagal tone is by measuring heart rate and heart rate variability. Lower heart rate and greater variability mean increased vagal activity. As part of the parasympathetic nervous system, the vagus nerve plays a significant part in stress regulation. It directly sends signals back and forth from many organs including the GI tract, informing the body how to respond to stress. It's a major factor in the body's ability to transition back and forth between sympathetic and parasympathetic states. In other words, it helps your body properly transition back and forth from fight or flight to rest and digest. As you know, eating while in fight or flight mode can negatively affect digestion. The connection between a low vagal tone and chronic inflammation could also explain why many gut conditions are often coupled with depression, anxiety, and other mood disturbances. The vagus nerve and the gut-brain don't only use the acetylcholine and GABA to communicate, they also use serotonin, dopamine, and norepinephrine to name a few. If vagal tone is low, inflammation can remain high with distress signals excessively sent from the gut to the brain via the vagus nerve. It's often found, for example, the depression and colitis encourage the development of one another. Studies have shown that when the vagus nerve is no longer connected, antidepressants lose their efficacy and neurotransmitter levels in the brain begin to normalize without medication. It's like an emergency telephone line. A healthy vagal tone has many advantages. Let's take a look at some more features of a healthy vagus nerve. First, it supports healthy motility or the movement of contents through and out of the GI tract. Recall that the sympathetic nervous system helps regulate motility, since having to go to the bathroom is not convenient when you're in the middle of escaping danger. It does this by sending a signal from the brain down to the stomach and the bowels when it's time for fight or flight. Further evidence that the vagus nerve is the telephone line between the gut and the brain, and that line works both ways. The stomach also tells the brain via the vagus nerve when stress is happening. The messages are sent using neurotransmitters or chemical signals like acetylcholine that are produced in the gut. Many chiropractors think that GI issues might be related to improper positioning of the spine which may affect how the gut sends signals along the vagus nerve. A connection here is plausible, considering that this nerve informs digestion. In fact, the upper GI tract in stomach are the organs in the GI tract with the most nerves. Therefore, they are more effected by the parasympathetic influence of the vagus nerve. The sympathetic nervous system can influence the GI muscle to speed up or slow down depending on stressors. As a result, the vagus nerve directly influences peristalsis which is the muscular relax that pushes food forward through the GI tract. An underactive vagus nerve delays emptying, slowing down digestion. The vagus nerve can also be a factor in the development or worsening of heartburn and other GI issues. The vagus nerve also helps regulate appetite by telling the brain when we're full. Distension of the stomach activates receptors which send signals back up to the brain. There are also chemical signals sent along the nerve via neurotransmitters, triggered by changes in pH and gastric juices. The vagus nerve also regulates insulin and glucose, and it's the main pathway that ghrelin, the hunger hormone, uses to communicate with the brain. All this in addition to the inflammatory reflex suggests that the vagus nerve may play a role in obesity. In studies on animals where the vagus nerve is cut, ghrelin no longer tells the brain they're hungry. Since the migrating motor complex is also governed by ghrelin, this too can be influenced by the vagus nerve. Let's talk about another way the vagus nerve influences health through our GI tract. The vagus nerve directly affects our B12 intake. The nerve stimulates the parietal cells in the stomach that secrete acid and intrinsic factor which the body needs to absorb B12. Studies show that when the vagus nerve is cut, B12 absorption is slightly impaired until the body can adjust. Because it's connected to digestive system, the vagus nerve has the ability to regulate nutrient absorption. It can trigger the pancreas to secrete insulin, and when the vagus nerve isn't activated, glucose levels are typically higher and insulin is lower pointing to a direct role in blood-sugar modulation. Now that we've talked about all the great things the vagus nerve can do, let's talk about its health. A person's vagal tone is an indicator of how well their vagus nerve is functioning. When a person is said to have high vagal tone, we're referring to the strength of their vagus nerve. High vagal tone implies that a person can easily transition between the sympathetic and the parasympathetic nervous systems, and is generally well equipped to deal with stress. A person with low vagal tone is less able to transition smoothly between sympathetic and the parasympathetic states, and is less able to cope with stress. Signs of healthy or high vagal tone are resilience to stress, good heart rate and heart rate variability, general sense of well-being, a healthy appetite, and healthy bowel movements. Signs of low vagal tone include inflammation, loneliness, depression, anxiety, elevated heart rate and blood pressure, heart attacks, and stroke. The key point to remember here is that those with the low vagal tone are more susceptible to chronic inflammation and have less of an ability to modulate the autonomic nervous system. Stimulating the vagus nerve can create a healthy response, but the key is to create balance. When the vagus nerve is over stimulated, it can cause reflux, loose stools, hiccups, bloating, and shortness of breath. We've talked about the importance of having a strong vagus nerve. So now let's take a look at common ways it can malfunction or become irritated. Irritation of the nerve can be triggered by excess consumption of spicy foods or alcohol. Stress releases hormones that override the parasympathetic nervous system. In these situations, the body knows that it has more pressing issues than to relax, and suppresses the functions of the vagus nerve. A high-fat diet reduces the parasympathetic response which can lower vagal tone. As you can see, a healthy diet and a lifestyle that includes effective stress management are important for maintaining the health of your vagus nerve. We'll talk about ways that you can strengthen the vagus nerve later on in this module. For now, let's recap. In this lecture, we went over various ways that the vagus nerve is involved with digestion and, therefore, can influence gut health. This mighty nerve also known as the wandering nerve extends all the way from the brain to the bowels, branching out to connect with the major organs through a network of nerve endings. The vagus nerve is like an information superhighway, it serves as a great example of how the body operates as an interconnected system. Were you aware of this incredible nerve before today? Share what you know, and what you were most surprised to learn in the Facebook group. Your moderators are there to support you and answer your questions. Thank you for joining me today. Good bye for now.