Lecture 2: Control of the gut- Nerves

Question 1

Where do you have conscious control of the gut?

Answer 1

At the entrance and the exit (external anal sphincters)

Question 2

How do we have unconscious control of the gut?

Answer 2

• autonomic nervous system (parasympathetic & sympathetic)
• enteric nervous system

Question 3

What is a ganglion?

Answer 3

Collection of cell bodies exisiting outside the CNS

Question 4

In the parasympathetic NS where does the post-ganglionic neurone lie?

Answer 4

Wall of the organ (viscera)

Question 5

Which branch of the autonomic NS stimulates the gut to start working?

Answer 5

Parasympathetic: often referred to as a cranio-sacral outflow (majority through the vagus nerve)

Question 6

Which branch of the autonomic NS diverts blood flow from the gut?

Answer 6

Sympathetic (T5-L2): thoraco-lumbar, not from the brain (reduces blood flow to the gut e.g. in fight or flight response and diverts it to muscles etc)

Question 7

Do the sympathetic nerves supplying the gut synapse in the sympathetic chain like the rest of the sympathetic nerves supplying the rest of the body?

Answer 7

No, they travel through the sympathetic chain and groups of nerves coalesce to form 3 splanchnic nerves.
They synapse with the prevertebral ganglia

Question 8

What are the names of the 3 splanchnic nerves?

Answer 8

• greater
• lesser
• least

Question 9

Where are the prevertebral ganglia located?

Answer 9

Lie anterior to the spinal chord

Question 10

Can the enteric NS operate on its own?

Answer 10

Yes

Question 11

How does the enteric NS exist?

Answer 11

2 plexuses, which are groupings of neurones which lie in 2 distinct layers

• submucosal plexus (Meissner’s)
• myenteric (Averback’s): b/w circular and longitudinal muscle layers

Question 12

What are the functions of the 2 enteric plexuses?

Answer 12

There is a lot of overlap in function of the 2 plexuses.
Submucosal: secretions and blood flow
Myenteric: gut motility