Your stomach really does have a mind of its own

The “little brain” in your gut and its fascinating connection to mental wellbeing

Everyone knows that the brain and the spinal cord, or the central nervous system (CNS) are pretty important. However, you probably haven’t heard of what is called “the little brain” in your gut, or even thought about how it could influence your mood.

Gut, brain, what!? How can this be?

Its official name is the enteric nervous system (ENS) and it is a densely packed collection of nerves which span your entire digestive tract. This system contains some 100 million neurons; roughly equivalent to the amount in the human spinal cord.

The enteric nervous system in all its glory. Image sourced from Stowers Institute for Medical Research (press release), Credit: Naomi Tjaden.
The enteric nervous system in all its glory. Image sourced from Stowers Institute for Medical Research (press release), Credit: Naomi Tjaden.

 

The enteric nervous system is involved in a large range of activities, including fluid exchange and local blood flow in the gut, regulation of stomach and pancreatic secretions, keeping hormone levels right, defence against nasty things you might ingest by vomiting or diarrhoea, and motility of food through the system.

If we take a look at motility in this diagram of the digestive tract, we can see that there are two distinct clusters of nerves, called plexuses (highlighted in blue).

Layers of the gastro-intestinal tract. Image by Goran tek-en sourced via Wikimedia commons CC BY 3.0
Layers of the gastro-intestinal tract. Image by Goran tek-en sourced via Wikimedia commons CC BY 3.0

The submucosal plexus is closest to the inside of the digestive tube and it makes sure that all these small flaps of tissue inside the intestine called ‘villi’ are moving around to absorb nutrients from the food that comes past.

Villi in the intestinal tract. Image from the Journal of Cell Biology, via Flickr CC BY 2.0
Villi in the intestinal tract. Image from the Journal of Cell Biology, via Flickr CC BY 2.0

The myenteric plexus is closer to the outside where it is imbedded in the muscles of the digestive tube. This means that it helps with all the mixing of contents and the ‘toothpaste tube’ squeezing (called peristalsis) of nutrients down the digestive tract.

Peristalsis helps move a ‘bolus’ of food down the intestine. Image from Auawise via Wikimedia Commons CC BY 3.0
Peristalsis helps move a ‘bolus’ of food down the intestine. Image from Auawise via Wikimedia Commons CC BY 3.0

So, now that we know a bit about what the enteric nervous system does you might be thinking “well that’s great, but there are neurons everywhere in the body, that doesn’t make them a second brain.” The reason this system is considered to be special is because it is capable of operating completely autonomously from the central nervous system.

There are other similarities to its big brother which led to this nickname the “little brain.” The ENS is made up of a range of different neurons, as well as support cells called glia, and it produces around 40 neurotransmitters (chemical messengers that transmit messages between neurons) of the same classes that are found in the brain (ie. serotonin and dopamine). To keep its environment stable the ENS has even created its own version of the blood-brain barrier to stop anything it doesn’t like from coming into its system.

 

Zombie gut

Once we realise that the gut is capable of acting independently of the brain we arrive at the horrifying and yet also fascinating possibility of a zombie gut.

Essentially, if you take a section of gut out of an animal (in this case a guinea pig) and place it in a petri dish, it will just keep on going about its everyday business – the mixing and peristalsis we discussed before.

Please see the video here (unfortunately could not imbed):

Zombie gut Just check out that peristalsis. Video courtesy of Ellis M and Bornstein JC (unpublished, used with permission), Department of Physiology, The University of Melbourne.

 

Those gut feelings: mental wellbeing and your gut

Image by Hey Paul Studios via Flickr CC BY 2.0
Image by Hey Paul Studios via Flickr CC BY 2.0

The enteric nervous system is capable of complete autonomy from the CNS, however, there is normally a connection between the gut and the brain in the form of the vagus nerve. In fact, scientists were amazed to discover that around 90 per cent of the signals passing along the vagus nerve come not from the brain above, but from the ENS.

Your gut is constantly communicating what’s going on to the brain, and it turns out, that when things aren’t going so well in the gut, this may also have an influence on your mental health.

Psychiatrists have long noticed that gastrointestinal problems are a common complaint of people who suffer from mental illness and recent research shows that there could indeed be connection.

Studies demonstrate that people with digestive system disorders such as Crohn’s disease, coeliac disease and irritable bowel syndrome are far more likely to suffer from mental health problems such as depression and anxiety than the general populace.

Given that all of the nutrition we require to function properly is obtained from food and fluids it does make sense that if our digestive system is not working properly due to nutrient deficiencies and inflammatory and immune responses then this distress could be communicated to the brain.

Interestingly, a relatively new therapy called vagal stimulation therapy has shown some success in individuals with ‘treatment resistant depression.’ This therapy involves stimulating the vagus nerve that leads up to the brain and has demonstrated that the gut could be much more important to our mood than was previously thought.

Whilst, we don’t often think about digestion as being of much importance I hope this has shown that it is not only overseen by a remarkably complex nervous system but could indeed influence your mood and mental health on daily basis.

The gut doesn’t have a very good name in today’s society, but I hope this article will encourage you to give some credit where credit is due.

 

 

 

 

To find out more, hit up these resources:

A really interesting video about how the gut microbiome could also be involved in mental health by its interaction with the vagus nerve through the ENS: https://www.youtube.com/watch?v=FWT_BLVOASI

http://www.theverge.com/2013/8/21/4595712/gut-feelings-the-future-of-psychiatry-may-be-inside-your-stomach

http://www.apa.org/monitor/2012/09/gut-feeling.aspx

http://berkeleysciencereview.com/the-second-brain-the-science-of-the-gut-continues-to-make-good-on-its-promise-to-aid-in-the-understanding-and-treatment-of-mental-disorders-and-beyond/

http://www.scientificamerican.com/article/gut-second-brain/

http://neurosciencestuff.tumblr.com/post/38271759345/gut-instincts-the-secrets-of-your-second-brain

 


2 Responses to “Your stomach really does have a mind of its own”

  1. ebyers says:

    Haha, isn’t it Ruth! I was so freaked out when I first saw it in my physiology lecture!

    It is possible for a psychological feeling such as nervousness to influence digestion – for example when you’re stressed the butterflies you feel in your stomach are from the “fight or flight” response your brain activates which diverts blood away from the digestive system to focus on more important things to get you through that situation. However, since only 10% of signals along the vagus nerve are going down there is a lot less of an influence in the opposite direction – especially since the vast majority of the signals going down from the brain are saying “yo, digestive system, theres some food comin’ your way, get ready.”

  2. Ruth de Jager says:

    Oh gosh, Zombie gut is terrifying!! Makes me think of weird sentience scenarios. Amazing that digestion could influence your psychological wellbeing. Does it go the other way too? Can psychological affect influence digestion? Great post! 🙂