We know that the brain is the main element in charge of controlling and managing the set of processes that take place in our body. But the truth is that the rest of the systems are also very important for the maintenance of the body and have the potential to influence its activity.

An example of this is the digestive system, thanks to which we can obtain the necessary nutrients to stay alive. Brain and stomach are related and communicate through nerve impulses and the transmission of chemicals.

Functional divisions of the nervous system

When we speak of the nervous system, we generally divide it into the central nervous system , in which we mainly find the brain and spinal cord , and the peripheral or autonomic nervous system, which corresponds to the set of nodes and nerves that innervate the different organs and cause the information from the organs to pass to the brain and vice versa.

Within the autonomic nervous system, we usually identify two basic subsystems, the sympathetic and the parasympathetic , which are in charge of managing the set of activities that the organism carries out in a way that is alien to our consciousness and of preparing our body to face dangerous situations (or to diminish the activation once the situation has passed).

However, there is a third subsystem of the autonomic nervous system, little studied and often ignored despite its tremendous importance for survival. It is the enteric nervous system, a part of our bodies related to the fascinating phenomenon of the dialogue between viscera and brain.

The Enteric Nervous System

The enteric nervous system is of paramount importance to the survival of the organism. It is the set of nerve fibres that innervate and control the functioning of the digestive system . It controls aspects such as the movement of the muscles of the digestive tract that allow food to reach the stomach, the secretion of acids and enzymes that dissolve food, the absorption of nutrients and the expulsion of waste.

This system is made up of millions of neurons (in a quantity similar to that of the spinal cord) distributed throughout the entire digestive tract. Although it is influenced by the sympathetic and parasympathetic systems, it is controlled by the enteric ganglia in a partially independent manner, acting in a reflex manner. It is not in vain that the digestive system has sometimes been called the second brain.

In this system also can be found a large number of hormones and neurotransmitters (particles that act as messengers between neurons), such as serotonin (of which most of what we have in our body is found and synthesized in this system, although it is also produced by the brain), dopamine, substance P or GABA among many others.

These neurotransmitters are regulated by the enteric system itself, although there is an influence on this system by those of the central system.

Stomach-Brain Nerve Communication

Although it has some independence, the enteric system and the central nervous system are linked and some central nervous system nerves connect to different organs in the digestive tract.

The vagus nerve is the main means of nerve communication between the brain and the digestive system. This nerve has great importance in different body systems; in the case of the stomach, it has been found that a two-way communication is established in which in fact the amount of information going from stomach to brain is greater than that going from brain to stomach.

That there is a greater transmission of information from the stomach to the brain than vice versa is due to the need to control intake . Feeding behaviour is governed by the brain, which causes the need for the brain to receive information on the good or bad functioning of the digestive system or whether consumption is harmful or beneficial, as well as whether the level of consumption is being excessive (feelings of satiety and hunger).

Despite this, the bum helps to control the activity of the intestine especially when the organism is in a situation of stress or danger. In that situation the sympathetic system contributes to stopping the functioning of the digestive system. When the dangerous situation passes, it is the vagus nerve that is mainly responsible for reactivating its functioning by acting on the parasympathetic level. It also participates in the emission of bile.

In addition, while the enteric system is capable of synthesizing and managing neurotransmitters, it is also affected by the functioning of the brain. Situations that generate stress or anxiety affect the enteric nervous system and its motility, as well as neurochemical imbalances such as those that occur during depression. Some of the hormones involved in this brain-digestive tube relationship are serotonin, noradrenaline and dopamine. Also acetylcholine, which is important for example in the functioning of the vagus nerve.

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The role of intestinal flora in communication

In addition to the role of nerve conduction and neurotransmitters, the intestinal flora also has an effect on the communication between the enteric nervous system and the central nervous system.

The microorganisms that populate our digestive tract have an influence on the enteric system’s ability to inform the brain of the good or bad condition of the system by modifying the secretion of neurotransmitters. Likewise, affects the functioning of the immune system , which in turn generates an indirect effect on behaviour and health status.

Various investigations with rodents also reflect that the functioning of the digestive system and the intestinal flora and fauna may even have an effect on behaviour through variations in the structure and functioning of the brain, altering the responses to certain neurotransmitters.

Effects of communication between brain and digestive system

The fact that the brain and the digestive system are connected is of great importance and has very relevant implications.The fact is that there is an influence by the digestive system on the functioning of the brain, and vice versa.

The presence of intestinal disorders can be linked to aspects such as anxiety , and it has been shown that the presence of anxious or depressive disorders can lead to the worsening or even appearance of digestive problems such as peptic ulcer or irritable colon.

It has even been detected that some of the microorganisms that cover our digestive system can generate antioxidant and anti-inflammatory substances that can positively affect our brain, stimulating protective cells called astrocytes and can delay neurodegeneration. This may make further research into these effects interesting.

But even today it is common that among the various guidelines recommended for some mental disorders there are mentions of dietary and eating aspects such as a lower consumption of certain substances or the following of specific diets (for example, increasing the level of tryptophan consumed, which in turn is related to the secretion of neurotransmitters).

Bibliographic references:

  • Guyton, A.C. (2001). Treatise on Medical Physiology. (10th ed.), McGraw-Hill Interamericana.
  • Look, J.C. (2012). The importance of the second brain. Discovery Health, 147.
  • Rothhammer, V. et al. (2016). Type I interferons and microbial metabolites of tryptophan modulate astrocyte activity and central nervous system inflammation via the aryl hydrocarbon receptor. Nature Medicine, 22; 586-597.