Lecture 12: Enteric Nervous System 1 Flashcards
What can the ENS produce?
complex behaviours without input from the brain
Where are most neurotransmitters and their receptors found?
in the ENS
What is the ENS?
network of neuron cell bodies, processes and axons in wall of gastrointestinal tract
largest part of the ANS
The axons and terminals of which neurons are found in the ENS?
visceral sensory neurons, sympathetic neurons and parasympathetic neurons
What does the ENS innervate?
all layers of GI tract including smooth muscle, mucosal epithelium and endocrine cells
Where does the ENS run?
the entire length of the GI tract from back of mouth to anus
What are the two ganglionated plexuses of the ENS?
myenteric plexus and submucosal plexus
Where is the submucosal plexus? Where is the submucosal plexus ganglionated?
present in stomach, but not ganglionated
ganglionated submucosal plexus begins at pylorus
Where does ganglionated myenteric plexus begin?
at upper esophageal sphincter
What is the extrinsic nerve supply of the ENS?
sympathetic nerves innervate whole length of GI tract
parasympathetic nerves primarily innervate upper and lower GI tract (less prominent in jejunum and ileum)
What do extrinsic sensory neurons (visceral primary afferents) innervate?
the full length
Where are extrinsic primary afferents that supply the upper GI tract? What proportion of vagal axons are primary afferents?
in the vagus nerve
90%
Where do dorsal root ganglion cells (spinal) afferents run?
in splanchnic and pelvic nerves
often thought to be nociceptive
What is different about vagal afferents and dorsal root afferents?
functions and central terminations
What are functions of the ENS?
controls movement of intestinal content
regulation of water and electrolyte transport across the mucosa
contributes to control of acid secretion in stomach, mucus secretion along length and bicarbonate secretion in duodenum
What do contractions of intestinal smooth muscle depend on?
the brain or spinal cord
What does the jejunum contain?
entire circuit for generation of a complex behaviour
circuit involves two types of cholinergic neurons
What are neurons that must be in the ENS?
intrinsic sensory neurons, excitatory motor neurons, inhibitory motor neurons, interneurons, secretomotor neurons, vasodilator neurons, intestinofugal neurons and interplexus neurons
How many different neuron subtypes may each ganglion contain?
20+ different neuron subtypes
How can functionally distinct enteric neurons be identified and put into circuits mediating behaviour?
top down approach -> define the properties specific neurons must have to produce an identified behaviour e.g. a neuron that has terminals in the muscle is likely to be a motor neuron
What is the Law of the Intestine?
a “physiological” stimulus applied to the intestinal wall will cause a contraction above the stimulus and a relaxation below
if a neuron sends an axon orally, then it is likely to be in an excitatory pathway, if its axon has terminals in the muscle then it may be an excitatory motor neuron
if a neuron sends an axon anally, then it is likely to be in an inhibitory pathway and if it has terminals in the muscle it may be an inhibitory motor neuron
What excites intestinal smooth muscle?
acetylcholine and substance P
What mediates inhibition in the muscle?
nitric oxide (NO) and a purine released by the same nerve terminals
What is immunofluorescence used to identify?
neurochemical codes of 2-3 antigens for many neuron subtypes
What does assigning function depend on?
projections and physiology
