The enteric nervous system, or ENS, is a network of nerve cells embedded in the walls of the gastrointestinal tract. It helps the gut sense its contents, organise movement, regulate secretions, and adjust local blood flow. Because many of these activities can be coordinated locally, the ENS is sometimes described as the gut’s “second brain”.
That phrase does not mean the ENS thinks or makes decisions like the brain. It highlights its size, organisation, and ability to manage many digestive processes without requiring a separate instruction for every local response. The central nervous system can still influence the gut through autonomic pathways.
Anatomy of the enteric nervous system
The gastrointestinal wall contains several layers with different jobs. The mucosa faces the gut’s contents and participates in secretion, absorption, and local sensing. Beneath it, the submucosa contains connective tissue, blood vessels, and the submucosal nerve network. Smooth muscle layers form the muscular wall that mixes and propels material through the tract.
The myenteric plexus, also called Auerbach’s plexus, lies between the circular and longitudinal muscle layers. It is especially important for coordinating contractions and relaxations. The submucosal plexus, also called Meissner’s plexus, lies closer to the mucosa and is closely involved in secretion, absorption, and local blood flow.
These plexuses are not isolated cables. They contain sensory neurons, interneurons, and motor neurons linked into circuits. Together they can detect stretch or chemical changes, process local information, and produce an appropriate response.
Enteric neurons
Enteric neurons are commonly grouped by what they detect, how they connect, and the response they help produce. Their names can be technical, but the overall pattern is straightforward: sense a change, process the information, and coordinate a response.
Primary afferent neurons
Primary afferent neurons detect conditions inside the gut. They can respond to stretching of the wall, changes near the mucosa, and chemical signals in the gut’s contents. Their information enters local enteric circuits and can also contribute to signals sent towards the central nervous system.
Motor neurons for circular and longitudinal muscle
Excitatory motor neurons help contract smooth muscle, while inhibitory motor neurons help it relax. Working in sequence, these signals allow one region to contract while the next region relaxes, supporting mixing and forward movement. Other motor neurons influence the longitudinal muscle layer and help shape the movement of the gut wall.
Ascending and descending interneurons
Interneurons connect sensory cells with motor cells and with other parts of the enteric network. Ascending pathways generally help coordinate activity towards the mouth, while descending pathways help organise activity towards the anus. These labels describe direction along the gut rather than the direction of a nerve impulse in every situation.
Secretomotor and vasomotor neurons
Secretomotor neurons influence glands and epithelial cells, helping adjust the movement of fluid and electrolytes into or out of the gut. Vasomotor pathways influence local blood vessels so that the active intestinal wall and mucosa can receive an appropriate blood supply.
Intestinofugal neurons
Some enteric neurons send information from the gut to autonomic ganglia outside the intestinal wall. These connections provide another route through which activity in one region can influence wider autonomic responses.
For a broader introduction to related automatic body functions, see the autonomic nervous system guide.
Neurotransmitters of the enteric nervous system
Enteric neurons communicate using chemical messengers. Acetylcholine commonly supports contraction and secretion, while nitric oxide and vasoactive intestinal peptide can contribute to relaxation and secretory responses. Serotonin, tachykinins, purines, and opioid peptides also participate in sensory signalling and local digestive circuits.
The effect of a messenger depends on the receptor receiving it, the cell involved, and the surrounding circuit. For that reason, one chemical messenger may have different effects in different parts of the gut. The ENS is best understood as a coordinated network rather than a list of isolated chemicals.
Functions of the enteric nervous system
Control of motility
The ENS coordinates contractions that mix food with digestive secretions and move contents along the tract. A typical peristaltic pattern combines contraction behind a bolus with relaxation ahead of it. Local reflexes help organise this pattern, while the brain and autonomic nerves can modify it.
Different regions have different timing and movement patterns. The stomach stores and mixes material, the small intestine mixes contents and supports absorption, and the colon moves and stores waste. The ENS contributes to each pattern without making every region behave identically.
Local blood flow and fluid exchange
Enteric circuits influence blood flow near the mucosa and help coordinate movement of fluid and electrolytes across the intestinal lining. Sympathetic pathways from outside the ENS can alter vascular tone, particularly when the body is responding to wider demands.
Regulation of gastrointestinal secretions
Secretions from the stomach, pancreas, intestinal glands, and mucosal cells are influenced by local neural circuits as well as hormones. This coordination helps match digestive fluids with the presence and composition of food.
Protective responses
Changes in motility and secretion can help the gut respond to irritation or unwanted substances. Protective reflexes may increase movement or fluid secretion, but persistent symptoms or substantial fluid loss require appropriate medical assessment.
Enteric–brain interactions
The ENS and central nervous system communicate in both directions. Signals from the gut can contribute to sensations such as fullness, discomfort, and nausea, while signals from the brain can alter motility, secretion, and sensitivity. The vagus nerve and spinal autonomic pathways are important routes in this communication.
Seeing, smelling, or anticipating food can begin digestive preparation before food reaches the stomach. Later, signals from the stomach and intestines help shape appetite and satiety. These examples show that digestion is managed by local gut circuits working alongside hormonal and brain-based control.
Summary
The enteric nervous system is an organised network within the gastrointestinal tract. Its myenteric plexus is closely associated with movement, while its submucosal plexus is closely associated with secretion, absorption, and local blood flow. Sensory neurons, interneurons, and motor neurons form local reflexes that coordinate digestion.
The ENS can operate with considerable independence, but it remains connected to the central nervous system. Together, these systems help the gut respond to its contents, maintain coordinated movement, and adapt digestion to the body’s changing needs.