The enteric nervous system (ENS) runs throughout the digestive tract and operates largely independently of the rest of the nervous system. Colloquially, it is also referred to as the abdominal brain. Basically, it is responsible for regulating everything that happens throughout the digestive process.
What is the enteric nervous system?
As the name suggests, the enteric nervous system is responsible for the entire digestive tract. It is referred to in English as the second brain or abdominal brain. Along with the sympathetic and parasympathetic nervous systems, it is the third component of the nervous system. As the second brain or abdominal brain, it has a similar structure to the brain and works on the same principle. It has been found to have approximately four to five times more neurons than the spinal cord. In the enteric nervous system, there are complicated circuits that ensure that digestive processes are precisely coordinated with each other. In doing so, it works largely autonomously. The necessary processes within the digestive tract are regulated independently. However, the ENS is also subject to the influences of the sympathetic and parasympathetic nervous systems. Of course, there are also connections to the main brain. Thus, the exchange of information between the enteric nervous system and the main brain is thought to influence intuitive decisions (gut feelings).
Anatomy and structure
The enteric nervous system represents a network of neurons that encompasses the entire digestive tract from the esophagus to the rectum. In this context, the main components of the ENS consist of two plexuses of nerves located within the intestinal wall. These are, on the one hand, the myenteric plexus (Auerbach’s plexus) and, on the other hand, the submucosal plexus (Meissner’s plexus). The myenteric plexus represents a complex of nerve cells in the annular and longitudinal muscle layer of the intestine. The submucosal plexus is integrated into the intestinal mucosa. In addition, other small plexuses are found below the serosa, in the ring muscles, and in the mucosa itself. In addition to the neurons, interstitial cells of Cajal (Cajal’s cells) exist. These are specialized muscle cells that can trigger muscle contractions independently of the neurons and thus represent a kind of pacemaker system similar to the cardiac pacemaker. Although the enteric nervous system works autonomously, it is influenced by the sympathetic and parasympathetic nervous systems. The sympathetic nervous system provides the reduction of motility and secretion within the digestive system. Conversely, the parasympathetic nervous system influences the ENS to increase motility and secretion.
Function and Tasks
The function of the enteric nervous system is to control the digestive process. In doing so, it regulates intestinal motility, ion transport associated with absorption and secretion, immunologic functions of the digestive tract, and gastrointestinal blood flow. The myenteric plexus is responsible for intestinal motility. It controls intestinal peristalsis and at the same time ensures the secretion of enzymes into the intestinal lumen. The myenteric plexus is also supported by the Cajal cells, which start the muscle movements. Although the Cajal cells are not neurons, they are included in the myenteric plexus. The submucosal plexus controls the fine movement of the intestinal mucosa. It is located in the thin layer of smooth muscle that is part of the mucosa. Together with the myenteric plexus, it regulates the peristalsis of the intestine. In addition, it autonomously controls the secretion of the glands of the mucosa. Furthermore, it is also involved in the regulation of immunological processes. The enteric nervous system analyzes food for nutrient composition, water content and salt content and decides on absorption and excretion. Furthermore, it fine-tunes the function of inhibitory and activating neurotransmitters. In this way, intestinal function is adapted to external conditions. For example, during concentration on other activities, there is inhibition of intestinal peristalsis. In other situations, intestinal motility is stimulated again. In this process, the enteric nervous system is constantly in communication with the main brain. However, 90 percent of the information flows from the ENS to the brain and only 10 percent in the reverse direction. This occurs in cases where toxins or pathogens enter the intestine.Then, for example, by sending out messenger substances, the brain orders central measures that lead to the normalization of digestive processes.
Diseases
As a rule, the enteric nervous system can autonomously regulate digestive processes. However, particularly sensitive people often react with gastric or intestinal disorders to stress or everyday problems. In these cases, dysregulation occurs within the ENS. This is referred to as irritable stomach or irritable bowel. The symptoms are non-specific. Nausea, vomiting, stomach pain, abdominal pain, flatulence, diarrhea or constipation may occur. The fine-tuning between inhibitory and activating digestive processes is disturbed. The symptoms are unpleasant, but the disease is not dangerous. Similar processes take place in the enteric and central nervous systems. The function of neurotransmitters is the same. The transmission of stimuli in the nerve cells also proceeds according to the same principle. Thus, it is quite possible that in sensitive people an excess of stimuli leads to an increased flow of information between the main brain and the abdominal brain. Irritable stomach and irritable bowel can be treated well by lifestyle changes, psychotherapeutic measures and medication. However, there are also congenital diseases of the digestive system that are based on the absence of nerve tissue in entire sections of the intestine. An example of such a condition is Hirschsprung’s disease. In this disease, ganglion cells in the submucosal plexus or myenteric plexus are absent in entire intestinal segments of the colon. This leads to increased formation of upstream parasympathetic nerve fibers, which secrete acetylcholine. The resulting permanent stimulation of the ring muscles causes the affected section of the intestine to contract permanently. The result is chronic intestinal obstruction.