Cholinergic system - parasympathetic nervous system

Question 1

What happens if you stimulate and inhibit the cholinergic system?

Answer 1

If you stimulate the cholinergic system it mediates the effect the parasympathetic nervous system and if you inhibit the cholinergic system you inhibit the effects of the parasympathetic nervous system

Question 2

Give an overview of the parasympathetic nervous system

Answer 2

• The pre-ganglionic neurones are found in the brainstem cranial nerves and in the sacral area.
• They have long pre-ganglionic fibres (lie very close to the end organs). You get the release of acetylcholine which bind to nicotinic acetylcholine receptors.
• There are short post-ganglionic fibres causing the release of acetylcholine release binding to muscarinic receptors.
• Cholinergic transmission mediate effects of parasympathetic nervous system

Question 3

What happens at a cholinergic synapse e.g between the postganglionic fibre and organ

Answer 3

• Acetylcholine is made from choline and acetyl CoA in the pre-synaptic neurone.
• Then it is transported into a vesicle, which gets released.
• The action potential passes down the axon which causes a depolarisation and an influx of calcium which causes the release of the neurotransmitter.
• This acetylcholine will act upon nicotinic acetylcholine receptors or muscarinic receptors (there are two types of muscarinic receptors – M2 and M3).
• The acetylcholine is then broken down by cholinesterase, forming choline which is recycled.
• Stimulating these receptors induces a biological response

Question 4

Describe direct and indirect regulation of the cholinergic system

Answer 4

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Question 5

How and where is acetylcholine made?

Answer 5

• Occurs in NMJ, ganglia, parasympathetic post-ganglionic fibres, CNS
• Choline: From diet (liver, fish)
• Taken up by choline carriers at pre-synaptic terminal
• Acetyl CoA: Produced by cellular respiration
• ChaT inhibitors (e.g. fa64a) are potentially dangerous
• Biological weapons
• Changes in choline levels and acetyl CoA production will both alter Ach levels/cholinergic transmission
• Link Ach synthesis to metabolic activity
• Inhibition can cause less stimulation of skeletal muscles

Question 6

Describe cholinergic transmission - release (Botox), what are the effects?

Answer 6

• Botulinum toxin (Botox) – causes the breakdown of the vesicles containing the acetylcholine, so it is not released.
• Acetylcholine cannot bind to the receptors.

Question 7

Describe cholinergic transmission - termination inhibition, what is the effect of acetylcholinesterase?

Answer 7

• Acetylcholinesterase breaks down acetylcholine forming choline which is taken back up, or Acetyl CoA is taken away.
• If we inhibit this breakdown – by using a cholinesterase inhibitor.
• These block the breakdown, so when acetylcholine is released it activates the receptors but does not get terminated as acetylcholinesterase is being inhibited, so you get increased stimulation of these receptors.
• Leads to a variety of responses (shown in diagram). Twitching and paralysis.

Question 8

Describe cholinergic receptor pharmacology

Answer 8

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