From Brain to Bowels-The Vagus Nerve_Final
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>> 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.