The enteric nervous system, also known as the "mini brain" of the gut, helps control gastrointestinal functions. It contains neurons that use various neurotransmitters to regulate motor neurons that control secretion and movement. There are two main types of enteric neurons - AH and S-type. The enteric nervous system receives parasympathetic innervation from the vagus nerve and sympathetic innervation from the spinal cord. It contains various sensory receptors and uses synaptic transmission including slow and fast EPSPs and IPSPs. Disorders can occur if this system is disrupted, affecting digestion, absorption, and elimination.

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

3. 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

9. T5
L2

10. 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

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. -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.

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

15. 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-α2 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.

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