Enteric nervous system Flashcards
What is the Enteric Nervous system?
3rd division of autonomic nervous system
‘Intramural plexus’
Intrinsic innervation of the GI tract, from the oesophagus to the rectum.
Has lots of interaction with the brain.
What does intrinsic innervation mean?
Everything needed to make the gut function is found within the gut itself.
If a portion was removed it could function outside the body.
Where is the ENS?
Clumps of ganglion cells and their fibre bundles in two collections in the depth of the wall of the GI tract - plexuses
Submucosal plexus - stomach and intestines only.
Myenteric plexus - full length of GIT.
Plexuses are extensively interconnected
What are the layers of the wall of the gut?
Longitudinal muscle
(Myenteric plexus)
Circular muscle
(submucosal plexus)
Submucosa
Mucosa
Where is the myenteric plexus?
Nearest to the outside of the wall
Myo = muscle
Myenteric plexus sits in between the two layers of smooth muscle in the GIT.
Where is the submucosal plexus?
Sits internal to smooth muscle layers, around the submucosa.
What are the smooth muscles?
Depends on the orientation of the smooth muscle cells.
Cells can line up around the lumen to form circular muscle, which squeezes the lumen when contracts.
Other cells line up along the tube to form longitudinal muscle which shortens as it contracts.
What are the types of neurones in the ENS?
Sensory/afferent neurones
Interneurones
Efferent/secretomotor neurones.
Effectors
What are afferent neurones?
Sensory neurones - detect the environment, have mechanoreceptors and chemoreceptors
These interact through normal synapses with interneurones, which are excitatory or inhibitory depending on the neurotransmitter.
What are efferent neurones?
Interneurones then interact with efferent neurones - bring about response via effectors.
Can be excitatory or inhibitory, depending on neurotransmitters.
There are many neurotransmitters, includes Ach, various peptides.
Efferent neurones then carry out motor and secretory short reflexes - short as it is entirely within the GIT.
What do enteric reflexes do?
Controls motility, secretion, and blood flow to the gut.
What is a motor reflex of the ENS?
Motor reflex e.g. peristalsis - movement along GIT.
Controlled mainly by the myenteric plexus.
Sensory neurones detect chemicals in the lumen of the gut, and the physical presence of food - expansion of GIT.
Sensory neurones convey information via axons to myenteric plexus.
Efferent neurones then control the effectors, which act through the smooth muscles.
Where does contraction of smooth muscles occur in the GIT?
Bolus rests on wall of GIT.
Neurones detect the presence of food.
Mucosal stimulation leading to distension.
Goes to ENS myenteric plexus, which can influence behind the bolus and in front via the efferents.
What is simultaneous contraction to produce movement?
Can have excitation of efferents behind the bolus.
Contraction of the circular muscle behind will make the lumen smaller and squeeze the bolus forwards.
Myenteric plexus can simultaneously stimulate inhibitory efferents in front of the bolus, which makes the lumen bigger by relaxation, so bolus can go through.
What is the secretory reflex of the ENS?
Secretory reflex - Submucosal plexus.
Submucosal plexus is close to the lumen, connects by synaptic interaction by sensory neurones, and also via myenteric plexus.
Response produces various secretions of gut means there must be signals back to the submucosal plexus.
Only produce appropriate secretions when required.
