The Second Brain
Many of us may be familiar with the term “It’s just a gut feeling”, but why has the term evolved?
The gut-brain axis sounds a little like a new sci-fi movie but actually, it’s probably one of the most important aspects of our overall health and staying well. 90% of our brain’s output goes into something called the pontomedullary area, it’s the lower two-thirds of the brain stem, and that goes into the vagus.
The microbiota, the gut, and the brain communicate through the gut-brain axis in a bidirectional way that involves the autonomic nervous system via this nerve called The Vagus. It is the tenth cranial nerve, extending from its origin in the brainstem through the neck and the thorax down to the abdomen. Because of its long path through the human body, it has also been described as the “wanderer nerve”. The autonomic nervous system is a control system that acts (largely unconsciously) and regulates many of our bodily functions such as the heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal and is in itself, subdivided into 2 branches: the sympathetic branch or the parasymathetic branch. These two branches work in a yin- yang way:
The sympathetic nervous system prepares the body for intense physical activity and is often referred to as the fight-or-flight response
The parasympathetic nervous system has almost the exact opposite effect and relaxes the body and inhibits or slows many high energy functions. The effects of the parasympathetic nervous system can be summarised by the phrase 'rest and digest'. Let's look at an example of how these two systems function in response to changes in the environment.
Sympathetic Nervous System
Meet Jim - Jim is hiking in the wilderness all by himself and enjoying the tranquillity of the great outdoors when he turns a corner and finds himself only feet away from a full-grown bear. In a fraction of a second, the brain recognises the animal in front of him as a bear and classifies it as a very big threat. Immediately, the sympathetic nervous system is activated and without any conscious control by Jim at all, several body functions are affected all at once:
Heart rate is increased. Increased heart rate results in an increase in oxygen and nutrients that reach the brain and muscles, preparing them to deal with whatever Jim will have to face.
The liver is stimulated to release glucose into the bloodstream providing more energy that will be ready to power the muscles in case it is needed.
The bronchioles in the lung are dilated to allow more air into the lungs, which will increase oxygenation of the blood and keep up with the increased flow of blood through the lungs due to the increased heart rate.
The pupils of the eyes are dilated. Because the sympathetic nervous system is often activated when people are surprised, pupil dilation is a visual cue that we use to read surprise on people's faces.
The adrenal glands are stimulated to secrete adrenaline and noradrenaline. The adrenal glands are a pair of hormone-producing glands located on top of the kidneys that respond to stress. Together, the adrenaline and noradrenaline secreted by the adrenal glands have the same basic effects as the nerves of the sympathetic nervous system by increasing heart rate, increasing bronchiole dilation, and increasing glucose release from the liver. In addition, noradrenaline is also known to increase alertness. It may seem redundant that these hormones have the same actions as the sympathetic neurons, but hormones have longer lasting effects than nerve impulses, so while the initial fight or flight response is mediated by neurons, these hormones serve to reinforce and help to sustain the response.
Digestive activity is inhibited. In the moment of truth, a person may need every last ounce of energy they can muster. If Jim makes it through this ordeal, then he'll have plenty of time to complete digestion of whatever he ate for breakfast.
The bladder is relaxed. After all, this isn't the time for a person to relieve themselves; there are more pressing matters at hand. In very extreme cases of danger where the chances of survival seem remote, crippling fear often takes over and people can lose bladder and bowel control.
The Parasympathetic Nervous System
By contrast, the parasympathetic nervous system is responsible for the body's rest and digestion response when the body is relaxed, resting, or feeding. It basically undoes the work of sympathetic division after a stressful situation. The parasympathetic nervous system decreases respiration and heart rate and increases digestion. Stimulation of the parasympathetic nervous system results in:
Construction of pupils
Decreased heart rate and blood pressure
Constriction of bronchial muscles
Increase in digestion
Increased production of saliva and mucus
Increase in urine secretion
The enteric nervous system (ENS) is another part of the autonomic nervous system that controls the functioning specifically of the gastrointestinal tract. The ENS is made up of two thin layers with more than 100 million nerve cells in them — more than the spinal cord! These cells line the gastrointestinal tract, controlling blood flow and secretions to help the GI tract digest food. They also help us “feel” what’s happening inside the gut.
As such we see that high levels of cortisol and adrenaline from stress the sympathetic nervous system dominates, inhibits the Vagus Nerve and thus has detrimental effects on the enteric nervous system and gastrointestinal tract overall. Here are some symptoms related to just the gut from the impacts of stress:
Altered motility
Changes in gastrointestinal secretions
Increased intestinal permeability
Decreased blood flow to the gut → impaired digestion and absorption
Decreased regenerative capacity of gut lining
Dysbiosis
Irritated and inflamed gut lining
Another concept to grasp is that “stress” as far as the body is concerned is mental, emotional and physical: be that running late for a meeting, waiting for a cancelled train (Southern Rail!!), having crossed words with our children or partners to fighting an infection, we must evoke a stress response.
The vagus nerve, could be referred to as the captain the the parasympathetic nervous system - it’s activation leads to the release of acetylcholine and stimulates muscle contractions in the parasympathetic nervous system, as such an anti-inflammatory pathway has been described through Vagus Nerve fibres, which is able to dampen peripheral inflammation and to decrease leaky gut, thus very probably modulating microbiota composition.
That Gut Feeling
The most important function of the vagus nerve is afferent, bringing information of the inner organs, such as gut, liver, heart, and lungs to the brain. In this direction - gut to brain: The Vagus Nerve is able to sense the microbiota metabolites through its fibres, to transfer this gut information to the central nervous system where it is integrated in the central autonomic network, and then to generate a response. For instance, fibres sense inflammatory bacterial byproducts, called LPS or endotoxin. LPS activate vagal afferent fibres and have been documented in depression and mood disorders.
In a different study healthy mice chronically treated with the probiotic strain Lactobacillus rhamnosus had reduced stress-induced corticosterone and anxiety - and depression-related behaviour - now that’s a gut feeling if ever I head one!
The other direction of travel (efferent) is brain to gut. Historically, the vagus has been studied as an efferent nerve and as an antagonist of the sympathetic nervous system. In the gastrointestinal tract, the activation of the parasympathetic nervous system increases bowel motility and glandular secretion. In contrast to it, the sympathetic activity leads to a reduction of intestinal activity and a reduction of blood flow to the gut, allowing a higher blood flow to the heart and the muscles, when the individual faces existential stress.
How to work on the Vagus
Working on the Vagus Nerve (VN) which in itself has anti-inflammatory properties, is of key interest to restore homeostasis in the microbiota-gut-brain axis.
You can indirectly stimulate your vagus nerve to relieve keyed up or shut down nervous system states. Remember, your vagus nerve passes through your belly, diaphragm, lungs, throat, inner ear, and facial muscles. Therefore, practices that change or control the actions of these areas of the body can influence the functioning of the vagus nerve through the mind-body feedback loop:
Humming: The vagus nerve passes through by the vocal cords and the inner ear and the vibrations of humming is a free and easy way to influence your nervous system states. Simply pick your favourite tune and you’re ready to go. Or if yoga fits your lifestyle you can “OM” your way to wellbeing.
Conscious Breathing: The breath is one of the fastest ways to influence our nervous system states. The aim is to move the belly and diaphragm with the breath and to slow down your breathing. Vagus nerve stimulation occurs when the breath is slowed from our typical 10-14 breaths per minute to 5-7 breaths per minute. You can achieve this by counting the inhalation to 5, hold briefly, and exhale to a count of 10. You can further stimulate the vagus nerve by creating a slight constriction at the back of the throat and creating an “hhh”. Breathe like you are trying to fog a mirror to create the feeling in the throat but inhale and exhale out of the nose sound (in yoga this is called Ujjayi pranayam, which I am learning to integrate into my life through the wonderful Annelise of Birchwood Yoga) and Heartmath
Valsalva Maneuver: This complicated name refers to a process of attempting to exhale against a closed airway. You can do this by keeping your mouth closed and pinching your nose while trying to breathe out. This increases the pressure inside of your chest cavity increasing vagal tone.
Cold showers: Exposing your body to acute cold conditions, such as taking a cold shower or splashing cold water on your face, increases stimulation of the vagus nerve. While your body adjusts to the cold, sympathetic activity declines, while parasympathetic activity increases
Connection: Laughter, whether this occurs in person, over the phone, or even via texts or social media in our modern world, can initiate regulation of our body and mind. Surround yourself with positive relationships and get rid of toxic ones my friends :)
Use Adaptogen Herbs and medicinal mushrooms
Adaptogen herbs help naturally lower high cortisol levels in several key ways. They help balance hormones; reduce inflammation due to their strong antioxidant, antiviral and antibacterial effects; have natural antidepressant effects; lower fatigue; and help balance blood sugar levels. Following are some of my favourite adaptogenic herbs that can help lower cortisol, including:
Ashwagandha
licorice root
holy basil
medicinal mushrooms, including reishi, Turkey tail and cordyceps
Rhodiola
I hope this blog, albeit a little long has been interesting for you.
In health, Tanya x