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INNERVATION OF GASTRO-
INTESTINAL TRACT
DIVISIONS OF ANS
. ENTERIC NERVOUS SYSTEM- [MINI BRAIN OF GUT]
. PARA SYMPATHETIC NERVOUS SYSTEM
. SYMPATHETIC NERVOUS SYSTEM
1.SUBMUCOSAL/ MEISSNER’S PLEXUS
2.MYENTERIC/ AUERBACH’S PLEXUS
ENTERIC NERVOUS SYSTEM
ENTERIC NERVOUS SYSTEM
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
TYPES OF ENTERIC NEURONSAH-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
PARASYMPATHETIC INNERVATION
S2, S3, S4
DORSAL VAGAL COMPLEX OF MEDULLA
SYMPATHETIC INNERVATION
T5
L2
SENSORY AFFERENTS SPLANCHNIC NERVES VAGAL FIBERS
-Mixed nerves-Sensory afferents 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
SENSORY RECEPTORS
1.Mechano Receptors
2.Chemo Receptors
3.Pain Receptors/ Nociceptors
4.Mesenteric Receptors
5.Thermoreceptors
SYNAPTIC TRANSMISSION IN ENS
1.Slow EPSPs
2.Fast EPSPs
3.Slow IPSPs
4.Presynaptic Inhibition
5.Presynaptic Facilitation
SLOW EPSPs
-In AH-type neurons receptor is Adenylyl Cyclase & 2nd messenger is cAMP.
-In S-type neurons receptor is Phospholipase C & 2nd messenger is free intra-neuronal Calcium.
Significance- Long-lasting responses of the gut effectors during physiological stimuli.
FAST EPSPs
Mediated by Acetylcholine acting on ionotropic nicotinic receptors
Significance- rapid transfer of information between elements of enteric microcircuits.
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
PRESYNAPTIC INHIBITION
-Mechanism for selective shutdown of a microcircuit
-Release of Histamine in response to food allergens & infectious agents
NE-α2 adrenoreceptor- supress fast & slow EPSPs
Seratonin supresses both fast & slow EPSPs
Opiates supress some fast EPSPs
ACH supresses some fast EPSPs
PRESYNAPTIC FACILITATION
-Action of CCK on Gall Bladder
-Mechanism of action of Prokinetic drugs like TEGASEROID & CISAPRIDE
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.
HIERARCHY OF NEURAL REGULATION
GASTRO INTESTINAL REFLEXES1.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 reflex3.Long Reflexes -Vago-vagal reflex -Swallowing reflex -Pain reflexes -Vomiting reflex -Chewing reflex -Defecation reflex
APPLIED ASPECTS1.Hirschprung disease/ congenital megacolon/ congenital aganglionosis2.Cardiac Achalasia3.Abolition of Deglutition reflex4.Dumping syndrome after vagotomy & gastric antrectomy for peptic ulcer5.Idiopathic gastric stasis6.Paralytic Ileus7.Incontinence8.Dysphagia- Nut cracker’s oesophagus9.Emesis/ Vomiting
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