Physiology III Enteric Nervous System (ENS)

  1. Roles of the ENS in gut function
    • 1. control gut motility
    • 2. control of transmucosal fluid exchange
    • 3. digestion & absorption of food stuff
    • 4. control gastric acid secretion
    • 5. regulate local blood flow
    • 6. interact with immune and endocrine cells of the gut
    • 7. maintain functional epithelial barrier between body tissue and gut lumen
  2. Intrinsic nervous system of the gut
    Enteric nervous system
  3. Extrinsic nervous system of the gut
    sympathetic and parasympathetic divisions of the autonomic nervous system
  4. ENS location of nerve cell bodies
    • Myenteric plexus ( Auerbach's)
    • Submucosal plexus (Meissner's)
  5. Parasympathetic nervous system fibers
    • Vagus nerves & Pelvic nerves with preganglionic fibers into enteric nervous system.
    • As you move down digestive tract, vagus innervation decreases.
  6. Sympathetic Nervous System Fibers
    Central nervous system----preganglionic fibers into sympathetic ganglion----postganglionic fibers into enteric nervous system or blood vessels
  7. Enteric motor neuron
    An efferent fiber that conveys excitatory information from the myenteric or submucosal plexus to smooth muscle or glands of the digestive tube
  8. Muscle motor neuron
    Can be excitatory or inhibitory motor neuron
  9. Secretomotor neurons
    Only excitatory in that they promote glandular secretion
  10. Excitatory motor neurons secrete
    • Neurotransmitters that increase contractile tone in the target muscle.
    • Example: ACh and Substance P
  11. Inhibitory motor neurons secrete
    • Neurotransmitters that induce relatation of the target muscle.
    • Examples: NO, VIP, ATP
  12. Major function of the digestive tube
    Motility, secretions, digestion, and absorption
  13. Vagus nerves innervate
    Motility of the esophagus, stomach, small intestine, proximal regions of the hindgut (cecum, ascending and proximal transverse colon) along with secretions of the gastric glands, pancreatic glands, and gallbladder
  14. Pelvic nerve innervates
    Distal transverse colon, descending colon, retal bulb and anal sphincter
  15. Sympathetic Nervous System neurotransmitters
    • Preganglionic nerve endings secrete ACh
    • Postganglionic nerve terminals secrete NE
  16. Parasympathetic Nervous System neurotransmitters
    Preganglionic nerve endings secrete ACh Postganglionic nerve terminals secrete ACh
  17. Acetylcholine binds to and activates what in the digestive tube
    Metabotropic muscarinic type 3 (Gq) and 2 (Gi) metabotropic receptors
  18. Vagal Sensory Neurons cell body location and signal flow
    • Cell bodies in nodose ganglion
    • Sensory endings embedded within the mucosa and muscular layers of the gut wall. Vagal afferents connect with interneurons in the nucleus tractus solitarius and the dorsal motor nucleus of the vagus.  Activates vagal preganglionic efferent fibers that exit the dorsal motor nucleus and relay info to gut. Vago-vagal reflex
  19. Vagal mechaonosensitive afferent nerves
    Low threshold tension detectors activated at physiological levels of distension
  20. Vagal chemosensitive afferent nerves
    Relay information on luminal pH, osmolality, and nutrient concentration. Receptor endings do not sample lumen composition directly but instead process responds to local release of serotonin from gut enterochromaffin cells or gut hormones
  21. Vago-vagal Reflex
    Regulates moment-to-moment adjustments in motility of the distal esophagus, stomach, and small intestine as well as secretions of the gastric glands and intestinal crypts
  22. Spinal Sensory Neurons
    Called general visceral afferent fibers and have their cells bodies in the spinal ganglion. Use sympathetic pathway to make spinal sympathetic reflex.  They are the afferent limbs of inhibitory intestino-spinal reflexes
  23. Extrinsic Sensory Neurons and Relfexes
    Vagal sensory neurons, spinal sensory neurons, and intestinofugal neurons
  24. Intestinofugal neurons
    Subset of myenteric ganglion neurons which relay mechanosensory information directly to sympathetic prevetebral ganglion neurons. Respond to circular muscle stretch rather than tension.  Volume detector. Major function is to exert inhibitory feedback on motility of upstream gut segments.  Nerve cells bodies in myenteric plexus and project their efferent endings to prevertebral ganglia
  25. Intrinsic Sensory Neurons
    Cell wall bodies embedded within the myenteric and submucosal plexues.  Project multiple axonal processes that conduct action potentials to their synapses with interneurons and motor neurons of the ENS.  Respond to chemistry of luminal fluid and mechanical distortion of the mucosa.  Absent in esophagus, few in stomach and abundant in small and large instestine
  26. Luminal contents activate 4 major effectors
    the enteroendocrine system, the nervous system, the gut immune system (GALT), and the nonimmune defense system of the gut
  27. Intestino-intestinal reflexs
    bypass the CNS and are apart of the intestinofugal neurons
  28. Enteroendocrine cells (EEC)
    sense luminal chemicals and release hormones that act via blood or locally on nerve cells, epithelial cells and immune cells
  29. Post Operative Ileus (POI)
    After surgery the digestive tract does not work properly due to the inhibitory input of the drugs used in surgery.  Want to get the gut working as fast of possible therefore need to eat something because not using the digestive tract is bad for it
  30. VIP
    Vasoactive intestinal polypeptide
  31. Norepinephrine (NE)
    Acts directly on α1-adrenergic receptors
  32. Intestinal paralysis
    sustained sympathetic input to the gut with reduced blood flow and closed sphincters
  33. Physiological ilues
    Transiently (brief) absence of gut contractions
  34. Paralytic ileus
    absence of gut contractions for several days or more, as is commonly seen after abdominal surgery and other surgeries.
  35. Ileus
    A disruption of the normal propulsive activity of the gastrointestinal tract
  36. Colic
    pain in the abdomen or pain in the belly region of the animal
Card Set
Physiology III Enteric Nervous System (ENS)
Enteric nervous system