Enteric Nervous System

Question 1

What is the enteric nervous system?

Answer 1

•The third division of the autonomic nervous system.

•The intrinsic innervation of the GI tract.
-Intrinsic = does not need external innervation to work.

Question 2

What are the two major plexuses of the enteric nervous system?

Answer 2

• Submucosal / Meissner’s plexus

* Myenteric / Auerbach’s plexus

Question 3

What does the enteric nervous system do?

Answer 3

• Controls motility
• Controls secretion
• Controls blood flow

Question 4

What is the enteric nervous system sometimes known as?

Answer 4

The intramural plexus, esp. when referred to as part of the ANS.

Question 5

What does the GI tract include?

Answer 5

• From oesophagus to rectum.
• Pancreas.
• Biliary system (gall bladder and liver).

Question 6

Where is the enteric nervous system?

Answer 6

In the wall of the GI tract.

Question 7

Where in the GIT is the submucosal plexus found?

Answer 7

In the stomach and intestines only.

Question 8

Where in the GIT is the myenteric plexus found?

Answer 8

Across the full length of the GIT.

Question 9

Where is the myenteric plexus histologically?

Answer 9

Between the longitudinal and circular muscle of the wall of the GIT.

Question 10

Where is the submucosal plexus histologically?

Answer 10

Within the submucosal layer

Question 11

Which afferent neurones are found in the enteric nervous system?

Answer 11

Mechanoreceptors and chemoreceptors.

Question 12

Are the efferent neurones of the enteric nervous system excitatory or inhibitory?

Answer 12

Both.

This means many neurotransmitter are used.

Question 13

Which property of the enteric nervous system makes it able to be independent of external innervation?

Answer 13

It has many short reflex arcs.

Question 14

What do enteric reflexes do?

Answer 14

Control:

• Motility
• Secretion
• Bloody flow to the gut.

Question 15

What is an example of a motor reflex in the enteric nervous system?

Answer 15

Peristalsis

Question 16

On which plexus(es) of the enteric nervous system do the motor reflexes depend?

Answer 16

The myenteric plexus.

Question 17

In the gut, why is it important that mucosal stimulation and distention of the lumen causes both excitatory and inhibitory stimulation of smooth muscle?

Answer 17

• 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.

Question 18

On which plexus(es) of the enteric nervous system do the secretory reflexes depend?

Answer 18

The submucosal plexus.

Question 19

What secretions can result from stimulation of secretory neurones in the GIT?

Answer 19

•Secretion of:

• Mucus
• Enzymes
• Acids

Question 20

On which plexus(es) of the enteric nervous system do the reflexes concerning blood flow depend?

Answer 20

Both myenteric and submucosal plexuses.

Question 21

Why is it important that the CNS can influence the GIT?

Answer 21

To allow for conscious control of some functions of the GIT, e.g. distension of the rectum.

Question 22

Why might age affect function of the GIT?

Answer 22

• Number of neurones in the GIT decreases with age.

- Impaired function of neurones with age.

Question 23

What is Chaga’s disease?

Answer 23

• Caused by a parasite.
• Produces a toxin that affects neurones, possibly of the ENS.
• Can cause death of neurones of the ENS.

Question 24

What is achalasia?

Answer 24

• Difficulty swallowing.
• Autoimmune disease of inhibitory neurones of the ENS.
• Hinders peristalsis.

Question 25

What is Hirschprung’s disease / megacolon?

Answer 25

• 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.

Question 26

Why can Hirschprung’s disease cause colitis?

Answer 26

• Slow moving faeces in the GIT create a suitable environment for bacteria.
• Colon inflames in response to large numbers of bacteria (colitis).

Question 27

What is a treatment for Hirschprung’s disease?

Answer 27

Surgically removing the section of GIT that is not innervated.

Question 28

How might the enteric nervous system contribute to the development of Parkinson’s disease?

Answer 28

Enteric neurones are a site of entry of ‘pathogen’.

Question 29

List 3 general neurological conditions that can affect the ENS.

Answer 29

• Parkinson’s disease
• Peripheral neuropathies
• Myasthenia gravis

Question 30

Which syndrome is a result of the dysfunctional interaction between the CNS and the ENS?

Answer 30

Irritable bowel syndrome.

Question 31

What receptors in the ENS does loperamide (Imodium) target? What does it do?

Answer 31

Opioid receptors.

Decreases GIT motility by inhibiting the peristaltic motor reflex.

Question 32

List two drugs (other than loperamide) that target opioid receptors.

Answer 32

Morphine and codeine (both analgesic drugs).

Question 33

What is a possible side effect of morphine and codeine use? Why?

Answer 33

Constipation.

Act on opioid receptors to decrease GIT motility by inhibiting the peristaltic motor reflex.