7. The classification of enteric neurons according to
their morphological characteristics
1. DOGIEL TYPE – 1 NEURONS :
uniaxonal and have several short dendrites
2. DOGIEL TYPE – 2 NEURONS :
have smooth cell bodies and multiple axons
Brehmer, A., Schrödl, F., and Neuhuber, W. (1999). Morphological classifications of enteric neurons -
100 years after Dogiel. Anat. Embryol. (Berl). 200: 125–135.
8. TYPES NUMBER OF
PROCESSES
DENDRITES EXAMPLES FUNCTION
DOGIEL TYPE 1
NEURONS
4-20 DENDRITES
1 Axon
Short, thick
,flat
1. Ascending interneurons
2. Descending interneurons
3. Longitudinal muscle motor
neurons
4. Excitatory circular muscle
motor neurons
5. Inhibitory circular muscle
motor neurons
Motor
DOGIEL TYPE 2
NEURONS
1-16 Dendrites
1-4 Axon
Long , thin .
Much longer
than type 1
dendrites
Primary afferent neurons
(PANs) or
Enteric primary afferent
neurons (EPANs) or
Intrinsic primary afferent
neurons (IPANs)
Sensor
(Secretomotor)
9. ENTERIC NEURONS
S.n
o
CELLS AND NEURONS NEUROTRANSMITT
ERS
FUNCTION
1. Enterochromaffin cell Serotonin Activates the IPANS via 5-HT3 receptors
2. IPAN’S Ach Initiates PERISTALIC and SECRETOMOTOR
REFLUX
3. Ascending myenteric
interneurons
Ach , Sub P Activates ascending interneurons
4. Descending myenteric
interneurons
Ach , Serotonin ,
ATP
Activates descending interneurons
5. Ascending EXCITATORY
interneurons
Ach , Sub P Elicits contraction of smooth muscle via M3
& NK1 receptors
6. Descending INHIBITORY
interneurons
VIP , NO ,NPY ,ATP Elicits relaxation of smooth muscles
7. Secretomotor and
Vasomotor neurons
Ach , VIP Elicits Vasodilation & Glandular secretion
10. S.no NEURONS NEUROTRANSMITT
ERS
FUNCTION
8. Modulatory myenteric
neurons
Serotonin Elicits presynaptic activation of Ach
release via 5-HT4 receptors
9. Modulatory myenteric
neurons
dopamine Elicits presynaptic inhibition of Ach
release by activation of D2 receptor
10. Vagal preganglionic
neuron
( from CNS )
Ach Activates MYENTERIC and
SUBMUCOSAL ganglionic neurons via
NICOTINIC receptors
11. Sympathetic prevertebral
neuron
Nor-Adrenaline Inhibits secretion and
vasoconstriction
Benarroch, E.E. (2007). Enteric nervous system: Functional organization and
neurologic implications. Neurology 69: 1953–1957
11. Primary afferent neurons / enteric primary afferent neurons
(EPANs)
Present in submucosal ganglia and myenteric ganglia
These neurons responds to
luminal chemical stimuli
Mechanical deformation of the mucosa
---microbes &inflammation causes mucosal
damage /injury
Muscle tension ---- condition in which muscles of the
body remain semi-contraction for an extended period
12. LUMINAL CHEMICAL STIMULI( cholera toxin , heat liable enterotoxin( E.Coli ) .
MECHANICAL DEFORMATION OF MUCOSA
MUSCLE TENSION
• ACTIVATES
• ENTERIC CHROMAFFIN CELL
RELEASE
SEROTONIN
STIMULATES
5-HT RECEPTORS IN SUBMUCOSAL IPANS
LEADS TO INITIATION OF
PERISTALIC AND SECRETORIC REFLEXS
13. Serotonin
5-HT is a key mediator of sensory and motor function in the GI
tract
> 95% 5- HT in the body is contained within enteric nervous system
PERISTALIC REFLUX
PROXIMAL CONTRACTION 5-HT DISTAL RELAXATION
Stimulation of 5-HT4 receptor Stimulation of 5-HT 3 receptor
on IPANS on IPANS
Activation of interneurons Activation of interneurons containing
containing Ach &CGRP NO & VIP
Increased contractility decreased contractility
17. SECRETORY
REFLUX
Physio of Gastric & Intestinal Secretions ,
memorang
Secretomotor neurons
activated by Ach
released by the IPAN’s
and also activated by
Ach released from the
parasympathetic
(vagus neuron/ Cranial
nerve X ) neuron
causes the activation
of secretomotor
neuron releases the
Ach and VIP which act
on secretory glands
causes secretion
18. ENTERO TOXINS: Cholera toxin
(CT) is produced by vibrio cholerae and
is responsible for cholera, which is a
serious
epidemic disease characterized by
severe diarrhoea and dehydration
CT-induced intestinal secretion is
mediated by 5-HT release from
enterochromaffin cells .
Released 5-HT induces water and
electrolyte
secretion via stimulation of 5-HT2
receptors on enterocytes.
5-HT activates afferent sensory nerves
mainly through stimulation of 5-HT3
and 5-HT4 receptors.
They project to the myenteric plexus
and are also directly connected to
secretomotor neurons.
CT-induced secretion can be blocked by
Popoff, M.R., and Poulain, B. (2010). Bacterial
toxins and the nervous system: Neurotoxins and
multipotential toxins interacting with neuronal
cells. Toxins (Basel). 2: 683–737.
19. ENS : is refered as SECOND BRAIN of our
boby
GUT contain 100 - 300 million neurons
Because has its own peristalic and secretory
reflexes, independent of the brain and
spinal cord
The enteric nervous system includes efferent neurons ,
afferent neurons, and interneurons, which make the enteric
nervous system capable of carrying reflexes and acting
an integrating center in the absence of CNS input.
20. REFERENCE
1. BENARROCH, E.E. (2007). ENTERIC NERVOUS SYSTEM: FUNCTIONAL ORGANIZATION AND
NEUROLOGIC IMPLICATIONS. NEUROLOGY 69: 1953–1957.
2. GWYNNE, R.M., AND BORNSTEIN, J.C. (2007). SYNAPTIC TRANSMISSION AT
FUNCTIONALLY IDENTIFIED SYNAPSES IN THE ENTERIC NERVOUS SYSTEM: ROLES FOR BOTH
IONOTROPIC AND METABOTROPIC RECEPTORS. CURR. NEUROPHARMACOL. 5: 1–17.
3. POPOFF, M.R., AND POULAIN, B. (2010). BACTERIAL TOXINS AND THE NERVOUS SYSTEM:
NEUROTOXINS AND MULTIPOTENTIAL TOXINS INTERACTING WITH NEURONAL CELLS. TOXINS
(BASEL). 2: 683–737.
4. COSTA, M. (2000). ANATOMY AND PHYSIOLOGY OF THE ENTERIC NERVOUS SYSTEM. GUT
47: 15IV–19.
5. BREHMER, A., SCHRÖDL, F., AND NEUHUBER, W. (1999). MORPHOLOGICAL
CLASSIFICATIONS OF ENTERIC NEURONS - 100 YEARS AFTER DOGIEL. ANAT. EMBRYOL.
(BERL). 200: 125–135.
