Enteric Nervous System: parts and functions

This network of nerve cells associated with the digestive system are an essential component of the body.

The enteric nervous system is the part of the autonomic nervous system system in charge of regulating vital gastrointestinal functions. Among these functions is the regulation of esophageal, stomach and colorectal functions, which in turn involves the absorption and digestion of nutrients, as well as the maintenance of protective mucous membranes. The functioning of this system is the most complex of all the elements that make up the autonomic nervous system.

Below we will see in more detail what the enteric nervous system is and what are some of its main functions and characteristics.

What is the enteric nervous system?

The enteric nervous system is the cellular structure responsible for controlling our gastrointestinal functions. This includes motility, secretion motility, secretion, local immunity and inflammation of the organs that make up the digestive system..

In other words, the enteric nervous system is responsible for regulating functions important for the ingestion, absorption, metabolism and digestion of food. It is also responsible for preventing diseases related to these activities.

The enteric nervous system originates in the cells of the neural crest (a structure generated during embryonic development), which, in turn, divides into two large intertwined branches of nerve cells. These branches are called "Meissner's submucosal" and "Auerbach's myenteric", and form the two main components of the enteric nervous system.

This system is recognized as the most complex part of the peripheral nervous system and is composed of a high concentration of neurons and glial cells. is composed of a high concentration of neurons and glial cells.. In fact, it contains the largest collection of neurons found outside the brain.

Origins and development of this system

The enteric nervous system is formed from embryonic development, from two main processes: cell proliferation and its differentiation with the great variety of glial cells and neuronal variants that make up the organism.

From the fourth week of gestation, part of the neural crest cells, which give rise to most of the enteric nervous system, migrate through the entire digestive tract..

The other part of the same cells, which contribute to a lesser extent to the formation of the ENS, migrate from the cranial region to the caudal region (i.e., from the head to the opposite end). The latter spread gradually through the gastrointestinal tract of the embryo in all its components:

• Anterior intestinewhich later forms the esophagus, the stomach and the duodenum (connecting structure of the stomach with the one in charge of regulating the absorption of substances: the jejunum).
• Middle intestinewhich will give origin to the small intestine, including its first proposition called "cecum"; the ascending colon, the appendix and a part of the transverse colon, called "proximal segment".
• Posterior intestinewhich makes up a part of the transverse colon called the "distal portion", as well as its descending part, the sigmoids (the "S" shaped parts of the colon) and the rectum.

Components of the ENS

As we saw before, the enteric nervous system is divided into two main segments that arise from the neural crest. Each of them contains a great variety of glial and nerve cells, and together they are responsible for regulating the ingestion, absorption and metabolism of everything we ingest. These segments, according to Oswaldo, et al. (2012), are as follows:

Meissner's submucosal plexus.

It develops in the small intestine and colon mainly, and is responsible for regulating digestion and absorption in the music and Blood vessels..

Auerbach's myenteric plexus

It is found throughout the digestive tract, and is responsible for coordinating the activity of the coordinating the activity of the muscular layers of the digestive tract..

4 types of neurons that conform it

The large number of enteric neurons in the healthy adult small intestine remains constant throughout most of adult life, which appears to be the result of a process of continuous renewal of neurons in the gut (Kulkarni, S. et al, 2017).

The neurons that are part of the enteric nervous system, and are therefore responsible for regulating our gastrointestinal activity are the following (Oswaldo, et al, 2012):

1. primary intrinsic afferent afferent neurons.

Being afferent, these are neurons that transport nerve impulses from the organs to the central nervous system. However, being primary neurons, they do not conduct sensory information directly, but do so through other cells located in the enteric epithelium (the cellular tissue that lines the enteric nervous system). In other words, their activity is mainly that of sensory transducers. and thus regulate physiological functions of the gastrointestinal tract.

2. Motor neurons

As their name implies, they are responsible for activating the muscular layers that make up the digestive tract, blood vessels and some glands. They are further divided into excitatory motor neurons (for example, acetylcholine), or inhibitory motor neurons (such as nitric oxide or GABA). The latter, inhibitory neurons, are responsible for regulating water secretion, blood flow and electrolyte release.

3. Interneurons

These are the nerve cells responsible for connecting primary intrinsic afferent neurons with motor neurons. They can be ascending or descendingdepending on whether they act from the head to the opposite end, or in the opposite direction.

5. Intestinofugal neurons

Its extensions are located outside the digestive tract and connect with the nerve ganglia to form a new ganglion called "prevertebral". Their main function is to warn about changes in the activity of the intestine, so they are mechanoreceptors. it is mechanoreceptors (secondary neurons (secondary neurons that fire action potentials in response to mechanical stimuli).

Main functions of the ENS and associated pathologies

According to Furness, 2012, the main functions performed by the enteric nervous system as a whole are as follows:

• Determine the movement patterns of the gastrointestinal tract.
• Control gastric acid secretion.
• Regulating the movement and fluids crossing the epithelium.
• Modify blood flow at the local level.
• Modify and regulate nutrient absorption.
• *Interact with the intestinal endocrine system and also with the immune system.
• Maintain the integrity of the epithelial barrier that divides the cells of the intestine.

Inadequate functioning of this system affects the functions described above. For the most part, the inadequate functioning of the ENS is related to neuropathies that hinder the control of muscle activity and mucosal fluid movement.. This is reflected in various conditions of the colon and digestive tract.

In addition, the inadequate functioning of the ENS can be congenital in origin or acquired during postnatal development. Generally, the latter occurs due to a secondary medical condition that significantly impairs the functioning of the ENS, although it can also occur due to an iatrogenic effect of a drug, or drug-induced neuropathology.