Control of gut nerves

Question 1

Describe the layout of the ANS

Answer 1

• Cell bodies reside in the CNS
• Each pathway has a preganglionic and a postganglionic neurone
• The preganglionic fibres synapse with an autonomic ganglion outside of the CNS.
• Postganglionic fibres synapse on peripheral effector organs.

Question 2

What neurotransmitter is released by preganglionic neurones?

Answer 2

ACh

Question 3

What neurotransmitter is released by postganglionic neurones?

Answer 3

ACh, neuropeptides, or norepinephrine

Question 4

What is the difference in neurone length between the parasympathetic nervous system and the sympathetic nervous system?

Answer 4

• Parasympathetic preganglionic neurones are really long and the postganglionic fibres are really short (found within their target organ).
• Sympathetic preganglionic fibres are relatively short whilst the postganglionic fibres are longer.

Question 5

What is the role of the parasympathetic nervous system in digestion?

Answer 5

• Acts as the ‘on’ switch for the gut
• Postganglionic fibres release ACh, gastrin releasing peptide, vaso-inhibitory peptide
• Preganglionic fibres synapse in the walls of the viscera
• Innervates smooth muscle and endocrine and secretory cells.

Question 6

Through which nerves does the parasympathetic nervous system affect the gut?

Answer 6

• Vagus nerve - this supplies the majority of sympathetic outflow to the gut.
• Pelvic splanchnic nerves (S2-S4)

Question 7

What is the role of the sympathetic nervous system in digestion?

Answer 7

• Acts as the off switch of the gut by reducing blood flow to viscera to reduce their function.
• Mainly innervates blood vessels

Question 8

Through which nerves does the sympathetic nervous system affect the guts?

Answer 8

• T5-L2
• Nerves do not synapse at the sympathetic chain; instead, a group of nerves coalesces to form abdominopelvic presynaptic splanchnic nerves.

Question 9

What are the names of the abdominopelvic presynaptic splanchnic nerves?

Answer 9

• Greater (T5-T9)
• Lesser (T10-T11)
• Least (T12)

Question 10

What do splanchnic nerves of the sympathetic nervous system synapse with?

Answer 10

• Prevertebral ganglia e.g. coeliac, renal, superior mesenteric, inferior mesenteric.

Question 11

Where in the gut does the vagus nerve innervate?

Answer 11

• Anywhere from the oesophagus to the transverse colon

Question 12

Where in the gut does the pelvic nerve innervate?

Answer 12

• Anywhere from transverse colon to the anus.

Question 13

What is the enteric nervous system?

Answer 13

• A division of the nervous system that has extensive connection with the ANS but can also operate completely independently.

Question 14

Where does the enteric nervous system exist?

Answer 14

From the oesophagus to the anus.

Question 15

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

Answer 15

• Submucosal (Meissner’s) found in the submucosa.
• Mainly involved with secretions and blood flow.

-Myenteric (Auerbach’s) found in between circular and longitudinal muscle.
- Mainly involved in gut motility.