Nicotinic and Muscarinic receptors, agonists and antagonists?

Question

Im having a bit of trouble getting my head around this for exams...

So nicotinic and muscarinic receptors are both cholinergic receptors? Does this mean Ach is the part that binds to the receptors, and if yes does it bind to both the nicotinic and the muscarinic, or are there different ones?

And...a muscarinic agonist is something (substance/toxin) that causes the muscarinic receptor to be over-stimulated, so does this mean that whatever this substance may be, it binds to the receptor even tho its not Ach, therefore causing all of the side effects of over stimulation, eg emesis, GIT motility, salivation...

And a muscarinic ANTagonist is something that slows down the 'receptibility' of the receptors, so if someone was exposed to a muscarinic agonist, could an antagonist be given to reverse the effects?

And what would happen if the body was only exposed to a muscarinic antagonist?

And would an inhibited nicotinic receptor cause paralysis?

Thankyou so much in advance!

Answer 1

Tried to answer the specific questions you asked.

1) Yes they both bind to acetylcholine but work in two different ways (one is an ligand-gated ion channel, the other is a 7 domain g-coupled protein receptor with a secondary messenger system).

2) Yes it does bind to both of these receptors (but they are not found together- one is post synaptic the other is on the effector organ/tissue)

3) An agonist just stimulates the receptor (this doesn't mean that it must over-stimulate the receptor), an antagonist prevents receptor stimulation. Some agonists are only partial agonists and do not produce a "good" response.

4) Many toxins work by "blocking" or antagonising the muscarinic receptor and cause paralysis. So yes depending on what drug you inject the result will be stimulation or inhibition.

5) Antagonists do not give the reverse effect they just do not produce a response. They have receptor affinity but can not cause activation and produce a reaction.

6) Like toxins a muscarinic antagonist would most likely cause paralysis.

7) inhibiting just one receptor won't do anything but mass inhibition will.

Hope this helps

Answer 2

nicotinic and muscarinic receptors are both found in the parasympathetic nervous system.here the nicotinic receptor is the preganglionic receptor and the muscarinic receptor is the post ganglionic receptor.in the parasympathetic NS the neurotransmitter is acetylcholine(Ach).

A muscarinic agonist would work similarily to Ach eg.s are muscarine and carbachol. and yes they would cause parasympathetic actions such as increased salivation,decreased heart rate etc.

muscarinic antagonist works oppositely to Ach..eg.

is  atropine.antagonists would reverse the actions such as decrease salivation and increase heart rate but this would be indirectly because the parasympathetic system isn't functioning therefore the sympathetic would!

if the body was exposed to antagonists only..then you would have increased heart rate causing hypertension,decreased salivation cauisng dry mouth inability to pass urine etc.

regarding the inhibited nicotinic receptors...it depends on where they are found.eg if they are found in the skeletal muscles they would cause paralysis ,if they are found in the preganglionic receptor they will affect smooth muscles and sweat glands.