Innervation of gastro intestinal tract

enteric nervous system

1. INNERVATION OF GASTRO-INTESTINAL TRACT

2. DIVISIONS OF ANS . ENTERIC NERVOUS SYSTEM- [ MINI BRAIN OF GUT] . PARA SYMPATHETIC NERVOUS SYSTEM . SYMPATHETIC NERVOUS SYSTEM

3. 1.SUBMUCOSAL/ MEISSNER’S PLEXUS 2.MYENTERIC/ AUERBACH’S PLEXUS ENTERIC NERVOUS SYSTEM

4. ENTERIC NERVOUS SYSTEM

5. NEUROTRANSMITTERS Excitatory motor neurons -ACH -Substance P Secreto motor neurons -ACH -VIP -Histamine Inhibitory motor neurons -ATP -Nitric oxide -VIP Others - Norepinephrine - Seratonin -GABA -Dopamine - Somatostatin - Leu-enkephaline -Met- enkephaline - Bombesin

6. TYPES OF ENTERIC NEURONS AH-TYPE S-TYPE - Multiple long processes -long lasting hyper polarizing potential -largest population of neurons in Myenteric Plexus - Single long axon with multiple short dendrites -Exhibit nicotinic fast EPSPs -Low RM Conductance and greater excitability -Max in Submucosal Plexus Application of TETRODOTOXIN abolishes APs in S-type but not in AH-type

7. PARASYMPATHETIC INNERVATION S2, S3, S4

8. DORSAL VAGAL COMPLEX OF MEDULLA

9. SYMPATHETIC INNERVATION T5 L2

10. SENSORY AFFERENTS SPLANCHNIC NERVES VAGAL FIBERS - Mixed nerves -Sensory a fferents from gut to spinal cord -Sympathetic efferents to gut -Cell bodies of sensory afferents are in dorsal root spinal ganglia -80% of vagal fibres are sensory afferents -transmit information from gut to CNS for processing

11. SENSORY RECEPTORS 1.Mechano Receptors 2.Chemo Receptors 3.Pain Receptors/ Nociceptors 4.Mesenteric Receptors 5.Thermoreceptors

12. SYNAPTIC TRANSMISSION IN ENS 1.Slow EPSPs 2.Fast EPSPs 3.Slow IPSPs 4.Presynaptic Inhibition 5.Presynaptic Facilitation

13. SLOW EPSPs -In AH-type neurons receptor is Adenylyl Cyclase & 2 nd messenger is cAMP . -In S-type neurons receptor is Phospholipase C & 2 nd messenger is free intra-neuronal Calcium . Significance- Long-lasting responses of the gut effectors during physiological stimuli.

14. FAST EPSPs Mediated by Acetylcholine acting on ionotropic nicotinic receptors Significance- rapid transfer of information between elements of enteric microcircuits.

15. SLOW IPSPs Eukephalins , Dymorphine and Morphine are slow IPSP mimetics NE-alpha 2 adrenoreceptor , Galanine , Adenosine, ATP Significance- shunting of blood by symp . stimulation during exercise

16. PRESYNAPTIC INHIBITION -Mechanism for selective shutdown of a microcircuit -Release of Histamine in response to food allergens & infectious agents NE- α 2 adrenoreceptor - supress fast & slow EPSPs Seratonin supresses both fast & slow EPSPs Opiates supress some fast EPSPs ACH supresses some fast EPSPs

17. PRESYNAPTIC FACILITATION -Action of CCK on Gall Bladder -Mechanism of action of Prokinetic drugs like TEGASEROID & CISAPRIDE

18. NEURO-MUSCULAR JUNCTION IN GIT -Site where NTs released from axons of motor neurons act on smooth muscle fibres & interstitial cells of Cajal . -Simpler structers than the motor end plates of Skeletal muscles. -NTs are released from multiple varicosities of motor axons which spread out along the axon. -This structural organization is an adaptation for simultaneous application of a chemical NT to a large number of muscle fibers from a small number of motor axons.

19. HIERARCHY OF NEURAL REGULATION

20. GASTRO INTESTINAL REFLEXES 1.Local Reflexes -control much of GI secretion, peristalisis , mixing contractions and local inhibitory effects. 2.Short Reflexes -Gastro-colic reflex - Entero -gastric reflex - Colono-ileal reflex - Ileo -gastric reflex - Intestino -intestinal reflex 3.Long Reflexes - Vago-vagal reflex -Swallowing reflex -Pain reflexes -Vomiting reflex -Chewing reflex -Defecation reflex

21. APPLIED ASPECTS 1.Hirschprung disease/ congenital megacolon / congenital aganglionosis 2.Cardiac Achalasia 3.Abolition of Deglutition reflex 4.Dumping syndrome after vagotomy & gastric antrectomy for peptic ulcer 5.Idiopathic gastric stasis 6.Paralytic Ileus 7.Incontinence 8.Dysphagia- Nut cracker’s oesophagus 9.Emesis/ Vomiting

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