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Enteric Nervous System : structure of the internal nervous system


 What is an Enteric Nervous System?

Enteric nervous system refers to the nervous system of the gastrointestinal tract. It is responsible for the coordination and regulation of many digestive processes. The enteric nervous system is composed of two main types of neurons: intrinsic neurons and extrinsic neurons. intrinsic neurons are neurons that are located within the gastrointestinal tract.

The enteric nervous system (ENS) is one of the main divisions of the autonomic nervous system. The ENS is composed of a mesh-like network of neurons that extends from the esophagus to the rectum. The ENS is responsible for the control of gastrointestinal motility and secretions. The ENS is sometimes referred to as the “brain in the gut” because of its complexity and the number of functions it controls.

What is an Enteric Nervous System
Enteric Nervous System

The Enteric nervous system (ENS) is a complex network of nerves that directly controls the gastrointestinal system. It is sometimes referred to as the brain of the gut, and is composed of two main plexuses: the myenteric plexus and the submucosal plexus. Both of these plexuses are interconnected and work together to control peristalsis, secretion, and motility. Although the ENS is able to operate independently of the central nervous system (CNS), the two systems are interconnected and communicate with each other.

Nervous system

  1. Nervous system
  1. Brain

  2. Cerebral hemispheres

  3. Diencephalon or interbrain

  4. Thalamus

  5. Hypothalamus

  6. Midbrain

  7. Cerebellum

  8. Pons

  9. Medulla oblongata

  10. The spinal cord

  11. The ventricular system

  12. Choroid plexus

List of nerves of the human body

The human nervous system is an amazingly complex network of nerve cells (neurons) that carry messages back and forth between the brain and spinal cord and the rest of the body. The nervous system is made up of the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which includes all the nerves that branch out from the brain and spinal cord.  The autonomic nervous system (ANS) is a part of the PNS that controls the body's involuntary functions, such as heart rate, blood pressure, digestion, and respiration.


  • Structure of the nervous system

  • Development of the nervous system

  • The spinal cord or medulla spinalis

  • The brain or encephalon

  • The hindbrain or rhombencephalon

  • The midbrain or mesencephalon

  • The forebrain or prosencephalon

  • Composition and central connections of the spinal nerves

  • Pathways from the brain to the spinal cord

  • The meninges of the brain and medulla spinalis

  • The cerebrospinal fluid

  • The cranial nerves

  • The olfactory nerves

  • The optic nerve

  • The oculomotor nerve

  • The trochlear nerve

  • The trigeminal nerve

  • The abducens nerve

  • The facial nerve

  • The vestibulocochlear nerve

  • The glossopharyngeal nerve

  • The vagus nerve

  • The accessory nerve

  • The hypoglossal nerve

  • The spinal nerves

  • The posterior divisions

  • The anterior divisions

  • The thoracic nerves

  • The lumbosacral plexus

  • The sacral and coccygeal nerves

  • The sympathetic nerves

  • The cephalic portion of the sympathetic system

  • The cervical portion of the sympathetic system

  • The thoracic portion of the sympathetic system

  • The abdominal portion of the sympathetic system

  • The pelvic portion of the sympathetic system

  • The great plexuses of the sympathetic system

The structure of the internal nervous system in the human body

The enteric apprehensive system in humans consists of a few 500 million neurons(inclusive of the numerous varieties of Dogiel cells),0.Five% of the number of neurons within the brain, 5 times as many as the one hundred million neurons within the human spinal wire, and approximately 2⁄three as many as inside the entire frightened system of a cat. The enteric fearful system is embedded within the lining of the gastrointestinal gadget, starting inside the esophagus and lengthening all the way down to the anus.

The neurons of the ENS are collected into two sorts of ganglia: myenteric (Auerbach's) and submucosal (Meissner's) plexuses. Myenteric plexuses are located between the inner and outer layers of the muscularis externa, whilst submucosal plexuses are located within the submucosa.

The ENS is a division of the autonomic anxious gadget, the opposite divisions being the sympathetic and parasympathetic, with which it has full-size connections.

Types of enteric neurons in the human body

  • Enteric neurons, also known as intrinsic primary afferent neurons, are sensory neurons located in the gastrointestinal tract. These neurons are responsible for relaying information about the gastrointestinal tract to the central nervous system. There are three types of enteric neurons: extrinsic primary afferent neurons, intrinsic primary afferent neurons, and enteric motor neurons. Extrinsic primary afferent neurons are located in the dorsal root ganglia and vagus nerve and send information about the gastrointestinal tract to the central nervous system.

  • There are two main types of enteric neurons in the human body: myenteric plexus neurons and submucosal plexus neurons. Myenteric plexus neurons are found in the myenteric plexus, which is located between the inner and outer layers of the muscularis externa. The submucosal plexus is located in the submucosa, which is the layer of the digestive tract below the mucosa. Both types of enteric neurons are responsible for the peristaltic movement of food through the digestive tract and for the secretion of digestive enzymes.

  • Approximately 20 forms of enteric neurons may be described by using their features (Brookes and Costa 2002; Furness 2006). Combinations of functions (morphology, neurochemical residences, cell physiology and projections to targets) help to outline every type. Amongst the 20 sorts, three training may be recognized, intrinsic number one afferent neurons (IPANs, additionally referred to as intrinsic sensory neurons), interneurons and motor neurons. IPANs stumble on the physical nation of the organs (as an instance, anxiety in the gut wall) and chemical features of the luminal contents (Furness et al. 2004). They react to these signals to provoke appropriate reflex control of motility, secretion and blood go with the flow. IPANs connect to each other, with interneurons and at once with motor neurons. Interneurons hook up with different interneurons and with motor neurons. Amongst the motor neurons are muscle motor neurons, secretomotor neurons, secretomotor/ vasodilator neurons and vasodilator neurons.

What is the role of the internal nervous system in the human body?

  • The internal nervous system (INS) is responsible for the coordination and control of the body's involuntary activity, such as the regulation of heart rate, respiration, digestion, and metabolism. It is also responsible for processing sensory information from the external environment and relaying it to the brain and spinal cord. The INS consists of the autonomic nervous system (ANS) and the enteric nervous system (ENS). The ANS is further divided into the sympathetic and parasympathetic divisions.

  • The internal nervous system is responsible for conveying information between the central nervous system and the organs of the body. The internal nervous system is made up of the autonomic nervous system and the enteric nervous system. The autonomic nervous system controls the body's involuntary functions, such as heart rate, blood pressure, and digestion. The enteric nervous system controls the function of the digestive system.

Control of Motility

  1. The gastrointestinal tract has an external muscle coat whose functions are to mix the meals so that it's miles uncovered to digestive enzymes and to the absorptive lining of the gut, and to propel the contents of the digestive tube. The muscle additionally relaxes to deal with improved bulk of contents, drastically in the belly. In humans, specifically, the colon also has an important reservoir function to keep the feces till defecation. The enteric reflex circuits adjust motion by means of controlling the pastime of both excitatory and inhibitory neurons that innervate the muscle. These neurons have co-transmitters, for the excitatory neurons, acetylcholine and tachykinins, and for the inhibitory neurons nitric oxide, vasoactive intestinal peptide (VIP) and ATP. There is likewise evidence that pituitary adenylate cyclase activating peptide (PACAP) and carbon monoxide (CO) make contributions to inhibitory transmission.

  2. The instances for passage of the contents thru the gastrointestinal tract vary relying on the character of the food, which include its quantity and nutrient content. The peristaltic interest of the esophagus takes meals from the mouth to stomach in about 10 seconds, in which the food is mixed with digestive juices. Gastric emptying proceeds over intervals of approximately 1-2 hours after a meal, the liquefied contents being propelled by means of gastric peristaltic waves as small aspirates into the jejunum at some stage in this time. The fluid from the belly is blended with pancreatic and biliary secretions to form the liquid content of the small intestine, called chyme. Chyme is blended and moves slowly alongside the gut, under the manage of mixing and propulsive movements orchestrated by means of the ENS, whilst digestion and absorption of vitamins takes place. The average transit time via the human small intestine is three-four hours. Colonic transit in healthy people takes 1-2 days.

  3. Intrinsic reflexes of the enteric fearful device are critical to the technology of the patterns of motility of the small and huge intestines. The major muscle movements inside the small gut are: mixing activity; propulsive reflexes that travel for only small distances; the migrating myoelectric complicated; peristaltic rushes; and retropulsion associated with vomiting. The enteric anxious machine is programmed to supply those exclusive outcomes. In evaluation to the gut, peristalsis in the stomach is an outcome of carried out electric events (sluggish waves) which might be generated in the muscle. The depth of gastric contraction is decided by way of the moves of the vagus nerves, which shape connections with enteric neurons inside the myenteric ganglia. The proximal belly relaxes to deal with the advent of food. This rest is likewise mediated through vagus nerve connections with enteric neurons. Thus, the primary integrative centers for manipulation of gastric motility are in the brainstem, while the ones for managing the small and massive intestines are inside the enteric anxious system. In most mammals, the contractile tissue of the outside wall of the esophagus is striated muscle, and in others, consisting of human beings, the proximal half or greater is striated muscle. The striated muscle part of the esophagus is controlled, through the vagus, via an integrative circuitry within the brainstem. Thus, although the myenteric ganglia are distinguished in the striated muscle part of the esophagus, they may be modifiers, now not essential to manage centers, for esophageal peristalsis.

  4. The clean muscle sphincters restrict and adjust the passage of the luminal contents between regions. In widespread, reflexes which might be initiated proximal to the sphincters relax the sphincter muscle and facilitate the passage of the contents, whereas reflexes which might be initiated distally limit retrograde passage of contents into extra proximal elements of the digestive tract.

  5. The development of the contents in an oral to anal path is inhibited when sympathetic nerve activity will increase. To gain this, transmission from enteric excitatory reflexes to the muscle is inhibited and the sphincters are contracted. The put up-ganglionic sympathetic neurons utilize noradrenaline as the primary transmitter. Under resting situations, the sympathetic pathways exert little impact on motility. They come into action while protecting reflexes are activated.

Regulation of fluid alternate and nearby blood float

  1. The enteric frightened machine regulates the movement of water and electrolytes between the intestine lumen and tissue fluid compartments. It does this through directing the activity of secretomotor neurons that innervate the mucosa within the small and massive intestines and manage its permeability to ions. Neurotransmitters of secretomotor neurons are vasoactive intestinal peptide (VIP) and acetylcholine. Secretion is included with vasodilatation, which gives a number of the fluid that is secreted. Most secretomotor neurons have cells in our bodies in submucosal ganglia.

  2. Fluxes of fluid, extra than the whole blood extent of the frame, go to the epithelial surfaces of the gastrointestinal tract every day. Control of this fluid movement via the enteric worried system is of prime importance for the maintenance of whole-body fluid and electrolyte balance. The biggest fluxes are throughout the epithelium of the small gut, with significant fluid motion also going on in the big intestine, belly, pancreas and gall-bladder. Water moves among the lumens of digestive organs and body fluid compartments in reaction to switch of osmotically energetic molecules. The greatest absorption of water, eight-9 liters according to day, accompanies inward flux of nutrient molecules and Na+ thru the activation of nutrient co-transporters, and the greatest secretion accompanies outward fluxes of Cl¯ and HCO3¯ within the small and large gut, gall-bladder and pancreas. In each of these organs, fluid secretion is managed by using enteric reflexes. In the small intestine and most of the colon the reflexes circuits are intrinsic, inside the enteric apprehensive system. They stabilize secretion with absorptive fluxes, and draw water from the absorbed fluid and from the circulation. The pastime of the secretomotor reflexes is beneath a physiologically critical control from inhibitory sympathetic nerve pathways that respond to adjustments in blood stress and blood volume via vital reflex centers.

  3. Local blood glide to the mucosa is regulated thru enteric vasodilator neurons so that the mucosal blood go with the flow is appropriate to balance the nutritive needs of the mucosa and to deal with the fluid trade among the vasculature, interstitial fluid and intestine lumen. There aren't any intrinsic vasoconstrictor neurons. Overall blood float to the intestine is regulated from the CNS, via sympathetic vasoconstrictor neurons. The sympathetic vasoconstrictor neurons act in concert with the autonomic control of other vascular beds, to distribute cardiac output with regards to the relative desires of all organs. Thus in times of need, even for the duration of digestion, the sympathetic can divert blood float faraway from the gastrointestinal tract.

Regulation of gastric and pancreatic secretion

  1. Gastric acid secretion is regulated each through neurons and by hormones. Neural law is through cholinergic neurons with cell bodies within the wall of the stomach. These get hold of excitatory inputs both from enteric assets and from the vagus nerves.

  2. Gastric secretion of HCl and pepsinogen within the belly, and secretion of pancreatic enzymes, is essentially dependent on vago-vagal reflexes. Enteric motor neurons are the final common pathway, however the roles of intrinsic reflexes are minor. Pancreatic secretion of bicarbonate, to neutralize the duodenal contents, is managed secretin, a hormone launched from the duodenum, in synergy with activity of cholinergic and non-cholinergic enteric neurons. Secretion into the gall-bladder and bicarbonate secretion in the distal belly also are nerve controlled.

Regulation of gastrointestinal endocrine cells

  1. Nerve fibers run near endocrine cells of the mucosa of the gastro-intestinal tract, a number that are underneath neural control. For instance, gastrin cells within the antrum of the belly are innervated by way of excitatory neurons that make use of gastrin liberating peptides as the number one neurotransmitter. Conversely, hormones launched through gastrointestinal endocrine cells have an effect on the endings of enteric neurons. In an experiment, the endocrine cells act like taste cells, that pattern the luminal environment, and release messenger molecules into the tissue of the mucosa, in which the nerve endings are determined. This is essential communication, because the nerve endings are separated from the lumen by way of the mucosal epithelium. A crucial communication is with serotonin (5-hydroxytryptamine, 5-HT) containing endocrine cells which set off motility reflexes. Excessive launch of serotonin can cause nausea and vomiting, and antagonists of the 5-HT3 receptor are anti-nauseants.

Defense reactions

  1. Enteric neurons are concerned in a number of protection reactions of the gut. Defense reactions encompass diarrhea to dilute and dispose of pollutants, exaggerated colonic propulsive pastime that takes place while there are pathogens in the intestine, and vomiting.

  2. Fluid secretion is provoked by using noxious stimuli, specifically with the aid of the intraluminal presence of certain viruses, bacteria and bacterial pollutants. This secretion is due in big part to the stimulation of enteric secretomotor reflexes. The physiological purpose is absolutely to rid the frame of pathogens and their products. However, if the pathogens weigh down the firm's ability to cope, the loss of fluid (diarrhea) can end up a critical threat to the organism.

Entero-enteric reflexes

  1. Signals between intestine areas are carried each by way of hormones (together with cholecystokinin, gastrin and secretin) and by way of nerve circuits. Entero-enteric reflexes adjust one location in terms of others. For instance, when vitamins input the small intestine, secretion of digestive enzymes from the pancreas happens. A collection of nerve circuits that convey alerts from one location of the gut, to sympathetic ganglia, and again to the intestine wall provide a regulatory gadget that is precise to the gastrointestinal tract. Neurons with cell bodies in enteric ganglia and terminals in prevertebral sympathetic ganglia shape the afferent limbs of those reflexes. These are known as intestinal fungal afferent neurons (IFANs) (Szurszewski et al. 2002).

ENS-CNS interactions

  1. The gastrointestinal tract is in a manner of verbal exchange with the CNS. Afferent neurons bring records about the country of the gastrointestinal tract. Some of this reaches awareness, which include pain and soreness from the gut and the conscious feelings of hunger and satiety, that are incorporated perceptions derived from the gastrointestinal tract and different alerts (blood glucose, as an instance). Other afferent indicators, regarding, for instance, the nutrient load in the small intestine, or the acidity of the stomach, do no longer usually reach attention. In turn, the CNS provides signals to govern the intestine, which can be, in most cases, relayed via the ENS. For example, the sight and smell of meals elicits preparatory activities inside the gastro-intestinal tract, inclusive of salivation and gastric acid secretion. This is called the cephalic segment of digestion. Swallowed food stimulates the pharynx and upper esophagus, eliciting afferent alerts which might be incorporated within the brainstem, and in the end offer efferent alerts to enteric neurons within the belly that cause acid secretion and elevated gastric quantity, in guidance for the advent of the food. At the opposite give up of the intestine, indicators from the colon and rectum are relayed to defecation centres inside the spinal twine, from which a programmed set of alerts is conveyed to the colon, rectum and anal sphincter to reason defecation. The defecation centers are underneath inhibitory control from better CNS regions, and inhibition that may be launched when it's miles chosen to defecate. The different vital influences are via sympathetic pathways, that have been discussed underneath the sections on manipulation of motility and law of fluid exchange and local blood float, above.

Maintaining the health of the internal nervous system in the human body

  • In order to maintain the health of the internal nervous system in the human body, it is important to understand the function of the nervous system and how it affects the body. The nervous system is responsible for transmitting information throughout the body, and it is composed of two main parts: the central nervous system and the peripheral nervous system. The central nervous system is made up of the brain and the spinal cord, and the peripheral nervous system is made up of the nerves that branch off from the spinal cord. The nervous system is responsible for transmitting information throughout the body via electrical impulses.

  • The serious consequences of not maintaining the health of the internal nervous system in the human body are becoming increasingly apparent. As our understanding of the nervous system improves, we are discovering just how important it is to keep this system functioning properly. A variety of diseases and disorders can arise when the nervous system is not functioning properly, ranging from relatively minor problems to life-threatening conditions. In order to maintain the health of the internal nervous system, it is important to understand how this system works and what can be done to keep it functioning properly.

Enteric Nervous System : structure of the internal nervous system

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