Enteric Nervous System (ENS)
The enteric nervous system (ENS) controls the digestive system, connecting through the central nervous system (CNS) and sympathetic nervous system. It has a web of sensory neurons, motor neurons, and interneurons embedded in the wall of the gastrointesinal system, stretching from the lower third of the esophagus right through to the rectum. The neurons of the ENS are arranged in two layers, the submucosal and myenteric plexuses of the gut wall. Image 1:The ENS is embedded in the lining of the gastrointestinal system.
- It has been estimated that the ENS actually contains more neurons than the whole of the spinal cord.
- The ENS processes a range of sensations, such as the nature of gut contents and gut distension, and integrates this information with input from the autonomic nervous system. In this way the ENS can guide and optimise the muscular and secretory activity of the gastrointestinal tract.
- Many of the ENS effector neurons are also innervated by parasympathetic motor neurons, so they act as effector neurons of the parasympathetic nervous system. For this reason the ENS is regarded as an integral part of the parasympathetic nervous system, but its specialized sensory neurons and independent processing make it rather more complex than a simple parasympathetic ganglion.
- The ENS displays sophisticated coordination and exhibits plasticity and learning in response to changing dietary habits or disruptions to the gut.
Structure and Function
The enteric nervous system contains between 200 and 600 million neurons and 20 different types of neurons. With such complexity, the enteric nervous system is sometimes referred as the "second brain" or "the brain in the gut".
Its neurons are grouped in thousands of ganglia which are either:
- Myenteric: organised in a network around the gut, which spans the length between the upper oesophagus and the internal anal sphincter and contains mostly motor neurons.
- Submucosal: localised in the small and large intestine with most of the primary afferent sensory neurons. ie conveying information to the brain..
Mammalia organisms form intimate interfaces with commensal and pathogenic gut microorganisms. Increasing evidence suggests a close interaction between gut microorganisms and the enteric nervous system (ENS), as the first interface to the central nervous system. Accumulating evidence suggests that the development and homeostasis of the ENS are mediated by luminal (the inner open space of the gut) microbial factors. In particular, pathogens may take advantage of ENS neurotransmitters to potentiate their action or even create an intestinal microenvironment suitable for their reproduction. In addition, the ENS may represent the first interface between the intestinal content and the CNS, thus explaining the intricate relationships behind intestinal microbes and their effects on CNS inflammation, behavior, and even actions.
- The enteric nervous system is capable of working independently of the central nervous system. The intestine is the only organ in the body that can function autonomously.
- When it needs to communicate with the brain it communicates through the vagus nerve and the Gut Brain Axis
- Like the nervous system itself, the enteric nervous system synthesizes serotonin, dopamine, opioids for pain, etc.
- It monitors acidity, promotes bowel movement, and monitors our defense levels.
- There’s evidence that it’s able to detect if there are any bacteria in the food we’ve eaten. If so, it will induce processes such as vomiting or diarrhea.
- Enteric neurons can regulate the vomiting reflex, which is particularly critical in those cases in which vomiting arises as a side-effect of medical treatments, including chemotherapies.
- Watson C, Kirkcaldie M, Paxinos G. The brain: an introduction to functional neuroanatomy. Academic Press; 2010 Sep 20.Available from: https://www.sciencedirect.com/topics/neuroscience/enteric-nervous-system(accessed 3.2.2021)
- Giuffrè M, Moretti R, Campisciano G, da Silveira AB, Monda VM, Comar M, Di Bella S, Antonello RM, Luzzati R, Crocè LS. You Talking to Me? Says the Enteric Nervous System (ENS) to the Microbe. How Intestinal Microbes Interact with the ENS. Journal of Clinical Medicine. 2020 Nov;9(11):3705.Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7699249/(accessed 3.2.2021)
- QBI ENS Available from:https://qbi.uq.edu.au/brain/brain-anatomy/peripheral-nervous-system/enteric-nervous-system (accessed 3.2.2021)