Enteric Nervous System Flashcards
What is the enteric nervous system?
•The third division of the autonomic nervous system.
•The intrinsic innervation of the GI tract.
-Intrinsic = does not need external innervation to work.
What are the two major plexuses of the enteric nervous system?
- Submucosal / Meissner’s plexus
* Myenteric / Auerbach’s plexus
What does the enteric nervous system do?
- Controls motility
- Controls secretion
- Controls blood flow
What is the enteric nervous system sometimes known as?
The intramural plexus, esp. when referred to as part of the ANS.
What does the GI tract include?
- From oesophagus to rectum.
- Pancreas.
- Biliary system (gall bladder and liver).
Where is the enteric nervous system?
In the wall of the GI tract.
Where in the GIT is the submucosal plexus found?
In the stomach and intestines only.
Where in the GIT is the myenteric plexus found?
Across the full length of the GIT.
Where is the myenteric plexus histologically?
Between the longitudinal and circular muscle of the wall of the GIT.
Where is the submucosal plexus histologically?
Within the submucosal layer
Which afferent neurones are found in the enteric nervous system?
Mechanoreceptors and chemoreceptors.
Are the efferent neurones of the enteric nervous system excitatory or inhibitory?
Both.
This means many neurotransmitter are used.
Which property of the enteric nervous system makes it able to be independent of external innervation?
It has many short reflex arcs.
What do enteric reflexes do?
Control:
- Motility
- Secretion
- Bloody flow to the gut.
What is an example of a motor reflex in the enteric nervous system?
Peristalsis
On which plexus(es) of the enteric nervous system do the motor reflexes depend?
The myenteric plexus.
In the gut, why is it important that mucosal stimulation and distention of the lumen causes both excitatory and inhibitory stimulation of smooth muscle?
- The muscle behind a bolus must contract to push the bolus along the GIT. Requires excitatory signal.
- As there will be multiple boli in the GIT, the muscle in front of a bolus must relax to ensure there is an open passage through which the bolus can move. Requires inhibitory signal.
On which plexus(es) of the enteric nervous system do the secretory reflexes depend?
The submucosal plexus.
What secretions can result from stimulation of secretory neurones in the GIT?
•Secretion of:
- Mucus
- Enzymes
- Acids
On which plexus(es) of the enteric nervous system do the reflexes concerning blood flow depend?
Both myenteric and submucosal plexuses.
Why is it important that the CNS can influence the GIT?
To allow for conscious control of some functions of the GIT, e.g. distension of the rectum.
Why might age affect function of the GIT?
- Number of neurones in the GIT decreases with age.
- Impaired function of neurones with age.
What is Chaga’s disease?
- Caused by a parasite.
- Produces a toxin that affects neurones, possibly of the ENS.
- Can cause death of neurones of the ENS.
What is achalasia?
- Difficulty swallowing.
- Autoimmune disease of inhibitory neurones of the ENS.
- Hinders peristalsis.
What is Hirschprung’s disease / megacolon?
- Congenital absence of ENS neurones at the colon.
- Section of GIT that has no innervation contracts and cannot perform peristalsis.
- Stasis in faeces movement at that section of GIT.
- Also causes dysfunctional rectoanal reflex.
Why can Hirschprung’s disease cause colitis?
- Slow moving faeces in the GIT create a suitable environment for bacteria.
- Colon inflames in response to large numbers of bacteria (colitis).
What is a treatment for Hirschprung’s disease?
Surgically removing the section of GIT that is not innervated.
How might the enteric nervous system contribute to the development of Parkinson’s disease?
Enteric neurones are a site of entry of ‘pathogen’.
List 3 general neurological conditions that can affect the ENS.
- Parkinson’s disease
- Peripheral neuropathies
- Myasthenia gravis
Which syndrome is a result of the dysfunctional interaction between the CNS and the ENS?
Irritable bowel syndrome.
What receptors in the ENS does loperamide (Imodium) target? What does it do?
Opioid receptors.
Decreases GIT motility by inhibiting the peristaltic motor reflex.
List two drugs (other than loperamide) that target opioid receptors.
Morphine and codeine (both analgesic drugs).
What is a possible side effect of morphine and codeine use? Why?
Constipation.
Act on opioid receptors to decrease GIT motility by inhibiting the peristaltic motor reflex.
