ESA consists of braid-like nervous tissue accumulations (plexuses) located in the wall of the oesophagus, stomach and intestinal tubes.
The number of nerve cells involved in the plexus formations has been estimated at over 100 million, which is more than the entire spinal cord contains.
The plexus formations are arranged in two concentric layers:
1/ myentericus plexus (Auerbach's plexus) located in the outer outer stronger smooth muscle layer between the transverse and longitudinal layers, and
2/ plexus submucosus (Meissner's plexus) located just outside the very mucous membrane of the gastrointestinal tract.
The nerve tissue braids consist of:
Enteric sensory neurons (afferent neurons) that collect information about the tension of the gastrointestinal tract wall, as well as various aspects of the composition of the gastrointestinal contents (type: acidity, water content, amount of digestive hormones, etc.),
Enteric motor neurons (efferent neurons) that affect smooth muscle and glandular cells of the wall of the gastrointestinal tract. Some of these correspond to postganglionic parasympathetic neurons.
Enteric interneuron which, in complex networks, coordinates the sensory signal inflow with the motor signal output,
Cajal's enteric interstitial cells (acro: ICC), which here are a kind of mixed form between neuron and glial cell and which direct the peristaltic work of the intestine via enteric motor neurons (to the smooth muscle).
Enteric glial cells which more or less embed the above components. The enteric glial cells are reminiscent of the astroglia in the CNS.
A large number of different neurotransmitters and neuromodulators have been identified in the enteric nervous system, e.g. acetylcholine, noradrenaline, dopamine, serotonin (5-HT).
Especially the rich presence of serotonin in the ESA, about 80% of the body's serotonin content, attracts a lot of interest. A link between disturbances in serotonin metabolism in the ESA and the very common and difficult-to-treat disease Spastic colitis (Colon irritably) is considered very likely.
The enteric nervous system receives pre- and postganglionic nerve fibers of both parasympathetic and sympathetic origin and transmits primary afferent nerve fibers to the CNS, especially via the n. vagus.
These inputs and outgoing connections to the CNS are NOT necessary for the proper functioning of the gastrointestinal tract. Here it turns out (in laboratory animals) that if all the nerve fibre connections of the esophagus and gastrointestinal tract with the brain and spinal cord are cut, the intestines apparently function normally, but with a certain functional impairment in the stomach and esophagus.
The tissue structure and ability of the enteric nervous system (ENS) to function without contact with the CNS has meant that the enteric nervous system is now sometimes counted as one of the three main parts of the nervous system. The other two are the peripheral nervous system (PNS) and the central nervous system (CNS). But so far, ENS is usually included in PNS.