Enteric Nervous System

Question 1

Where does the ENS run from?

Answer 1

Runs from oesophagus to rectum

Question 2

What does intrinsic innervation of the GIT mean?

Answer 2

All essential components are in the GIT, dont need connection elsewhere

Question 3

What are Nuclei in the GIT

Answer 3

Neurones axons clumped together

Question 4

Why is ENS known as a little brain?

Answer 4

Has network of neurones (80-100 million)

Question 5

What are the 2 major plexuses?

Answer 5

1. Submucosal (Meissners) plexus
2. Myenteric (Auerbachs) plexus

Question 6

Location of submucosal plexus

Answer 6

Stomach and intestine only

Question 7

Location of myenteric plexus

Answer 7

Full length of GIT

Question 8

Myenteric is sandwiched between two …… layers

Answer 8

Muscle

Longitudinal muscle
Circular muscle

Question 9

Submucosal plexuses between

Answer 9

Circular muscle
Submucosa

Question 10

Types of neurones found in the plexuses

Answer 10

Afferent (sensory) neurones
Interneurones
Efferent (secretomotor) neurones

Effectors

Question 11

What receptors are associated with afferent neurones

Answer 11

Sensory
Mechano
Chemo

Question 12

What are is the function of interneurones?

Answer 12

Coordinate input and output
Excitatory + inhibitory

Question 13

What effectors do efferent neurones?

Answer 13

Smooth muscle
Secretory glands

Question 14

What NTs does the efferent neurones use

Answer 14

ACh
Various peptides

Question 15

What do enteric reflexes do?

Answer 15

Control:
Motility
Secretion
Blood flow

Question 16

What plexus does the motor reflex involve?

Answer 16

Myenteric plexus

Question 17

What do mechanoreceptors detect?

Answer 17

Detect physical presence of food in GIT

Question 18

What do chemoreceptors detect?

Answer 18

Detect sensory chemicals released by food

Question 19

What is an example of a motor reflex

Answer 19

Peristalsis
Movement of food in a rhythmic Ashton along GIT

Question 20

How is bolus (food) pushed along the GIT via sensory info

Answer 20

1. Sensory receptors (mechano/ chemo) detect contents of lumen
2. Info from receptors transported into myenteric plexus
3. Info distributed via interneurones to alter impact of efferent neurones that interact with muscle layers

Question 21

Mechanism used to push food down GIT

Answer 21

1. Bolus stimulates mucosal sensory receptors
2. Infro to Myenteric plexus
3. Excitatory interneurones prod effect
4. Effect = smooth musce contraction, decreases size of lumen, pushes bolus forward
5. In front of bolus inhibitory interneurones = smooth muscles relax
6. Occurs simultaneously so smooth movement

Question 22

What is secretory reflex?

Answer 22

Food stimulates sensory receptors
Bring info to submucosal plexus
Interneurones - efferent fibres - secretory cells
Secrete into lumen helping digestion and lubrication
(Enzymes, mucus, acid)

Question 23

Is blood flow to gut adjusted by the ENS

Answer 23

Yes involves both plexuses
Blood flow matches to activity of the gut

Question 24

How is the CNS integrated with the ENS

Answer 24

Symp/ parasymp is an intermediate
Brain can override the ENS

Question 25

How does CNS influence vary along GIT

Answer 25

Once food swallowed ENS cant stop food travelling CNS controls sphincters so can control faeces

Question 26

What causes dysfunction in the GIT (associated with ENS)

Answer 26

- Age - Congenital absence of ENS neurones (genetic) - peristalsis stopped - Abolition of rectoanalreflex

Question 27

What range of diseases can affect ENS

Answer 27

Specific diseases General disease

Question 28

Specific Diseases associated with ENS:

Answer 28

1. Changas disease 2. Achalasia 3. Hirschprungs disease

Question 29

What is Changas disease?

Answer 29

Endemic in South America Parasite transferred into blood via insect bite Toxins prod that kills ENS neurones ENS shutdown so cant eliminate toxin

Question 30

What is Achalasia disease?

Answer 30

Affects oesophagus and oral cavity - hard to swallow Nutritional status decreased More common in elderly bc loss of inhibitory neurones in Myenteric plexus in - sphincter at opening of stomach - oesophagus

Question 31

General neurological conditions that affect ens

Answer 31

- Parkinson’s disease - Peripheral neuropathies - Myasthenia Gravis

Question 32

How is irritable bowel syndrome caused?

Answer 32

Dysfunctional interaction between brain and ENS

Question 33

Are there opioid receptors in ENS?

Answer 33

Yes bcs ENS releases opoid NT Target opoid receptors to change function of ENS and so GIT

Question 34

What is the active ingredient in anti- diarrhoeal agents and how they work

Answer 34

Loperamide that act at opioid receptors to reduce gut motility

Question 35

How do some pain meds (morphine/ codeine) cause constipation as a side effect

Answer 35

They are also opioids so thy can act on opioid receptors in the gut and reduce gut activity

Question 36

What are the 4 layers of small intestine superficial to deep

Answer 36

Serosa Longitudinal muscle Circular muscle Submucosa Mucosa

Question 37

Function of myenteric plexus

Answer 37

Increase tone of the gut Control velocity and strength of gut contractions via inhibitory and excitatory interneurones Controls GIT motility

Question 38

Function of submucosal plexus

Answer 38

Controls secretions Controls local muscles Controls absorption

Question 39

What are the two ways ENS works?

Answer 39

- Autonomously (reflexes) - Via para/ symp NS

Question 40

What are the causes of the symp ns overriding the ENS

Answer 40

- fight or flight - inhibits both plexuses - causes decrease in peristalsis, blood flow, absorption, secretion

Question 41

What are the causes of para NS overriding ENS

Answer 41

- rest and digest - stimulates both plexuses - causes increase in peristalsis, blood flow, absorption, secretion

Question 42

Difference between short and long reflex of ENS

Answer 42

Short more common, can act fast and only involve neurones of GIT Long uses integration of CNS

Question 43

Examples of long and short reflexes

Answer 43

Inhibition of stomach secretions and motility is an example of short reflexes, while the internal digestion of food and chemical secretions stimulation by senses are example of long reflexes.

Question 44

Other causes of dysfunction of ENS

Answer 44

Congenital absence of ENS neurones - genetic mutation Peristaltic wave halts at section missing ENS neurones - faeces cant pass and builds up, (distending colon) breeding ground for infection Abolition of rectoanalreflex - affects defection, manifests after birth