Vagus Nerve?

[FL_Medic]

The question of how does the atropine have an effect, has been answered. It works to counteract the ACh at the muscarinic receptor site.

The connection of the vagus nerve in the atrial/junctional tissue is the dendrite. The synapse is the space between the dendrite and the effector organ/tissue. In this case the SA/AV nodal tissue.

Atropine does not work directly on the vagus nerve. Insert "what happens in vagus, stays in vagus" here. The atropine is working on the muscarinic receptor site, where the ACh is taking effect. Similar to how Narcan competes with opioids at specific narcotic receptors. The blood is providing a mechanism for the drug to be circulated to the receptor sites. It will not have a direct effect on the vagus nerve.

For illustration purposes only:

Some patients with seizure disorders have a device implanted that will stimulate the vagus nerve prior to a seizure. This action increases the activity of the parasympathetic nervous system, slowing the generation of impulses in the CNS.

These patients will still respond to atropine, because the drug is going to blunt some of the actions of the PNS.

The patient that has had a heart transplant, on the other hand, won't respond well, if at all, to atropine because the vagus nerve no longer has direct effects on the heart. Atropine can work on the other organ systems that the vagus nerve innervates above the level of the transection.

Is that a better answer?

No I was just asking where my props were... I enjoyed your answer and understood it. Thanks though.

[fiznat]

Just to clean up things a bit. Acetylcholine (Ach) is released by the presynaptic neuron into the synaptic cleft. Once in the cleft the Ach binds with Ach receptors on the post-synaptic target (the SA node in this case). Acetylcholinesterase is the enzyme that breaks down Ach once it is released from the presynaptic neuron. This limits the action of the Ach. Atropine competes with the Ach to bind with the postsynaptic receptors. The difference is that atropine does not cause any postsynaptic events. It does not actually do anything to the Ach. In organophosphate(OP) poisoning, the OP binds with the Acetylcholinesterase, preventing it from breaking down Ach. This allows the Ach to exert its affects without being inhibited. Atropine is used so that the Ach cannot bind to the postsynaptic receptor in OP poisoning.

Ahhh I say tomato....

haha thanks for the clarification ER Doc.

[OzMedic]

Ahhh I say tomato....

haha thanks for the clarification ER Doc.

The distinction that ER Doc made is very important in the context of OP or nerve agent poisoning. As already mentioned Atropine blocks muscarinic receptors sites only! It is a very simple drug when learned in that context. Organophosphates/nerve agents work by binding, and in turn inactivating acetylcholinesterase. The flow-on effect is over-stimulation of muscarinic receptors by acetylcholine for which atropine helps by it's aforementioned action. This does nothing to help the actual problem of the inactivated acetylcholinesterase. Pralidoxime is the agent we use to reverse this inactivation by OP/nerve agents. The problem is that in a matter of hours the bond between OP's and acetylcholinesterase becomes what is called "aged" which means it is irreversible even after the administration of pralidoxime. This is not such a problem when farmer joe gets exposed to organophosphate and is transported to hospital in a timely manner with atropine to reduce the symptoms and gets the pralidoxime within a few hours. The ageing process in the case of weapons grade nerve agents such as sarin and VX takes milliseconds to minutes and all the pralidoxime in the world won't help! Atropine may help reduce the symptoms but also will not solve the problem. Do you think they tell the guys in the military this stuff when they issue them their atropine/pralidoxime autoinjectors and say "there you go son, you will be ok now"? :wink:

[ffmedic9588]

Wow great discussion. Excellent answers all around. We had to do a project in school on 4 drugs and atropine was one of mine and probably my favorite. I really enjoyed reading and watching this thread. Keep up the great work guys.

PS I hope someday I will be able to know and retain as much as you guys have in this thread.

[OVeractiveBrain]

Dendrites carry afferent signals to teh soma most often, axons carry efferent signals from the soma to targets. UNless the vagus nerve has some reverse conduction, action potentials targeting efferents (the SA and AV node primarily in terms of our discussion) are carried along AXONS not DENDRITES. Just an FYI aside.

OveractiveBrain

[AnthonyM83]

Do you think they tell the guys in the military this stuff when they issue them their atropine/pralidoxime autoinjectors and say "there you go son, you will be ok now"? :wink:

At the PD they tell you it'll give you maybe 15 minutes...but you still need to get yourself some medical help...but what I'm reading here is that it won't help at all, rather it will only slow down the progression of it? Or perhaps if you inject it prior to exposure, you'll get 15 minutes of "immunity"? I quite like this topic, btw...

[ERDoc]

Dendrites carry afferent signals to teh soma most often, axons carry efferent signals from the soma to targets. UNless the vagus nerve has some reverse conduction, action potentials targeting efferents (the SA and AV node primarily in terms of our discussion) are carried along AXONS not DENDRITES. Just an FYI aside.

OveractiveBrain

Incorrect. Neurons are either afferent or efferent. If they carry information to the CNS they are considered afferent and if they take information from the CNS to the periphery they are efferent. The signals enter the neuron through the dendrite (at least in those neurons that have them) and they travel down the neuron to the the axons which form the synapse with whatever they synapse on. Your use of the terms afferent and efferent are incorrect. 10 points for anyone that can say which neurons do not have dendrites.

[FL_Medic]

hippocampal? unipolar?

[DwayneEMTP]

"Unipolar cells have one primary process that give rise to several branches. One of these is the axon and the rest serve as dendritic receiving structures. Unipolar cells have no dendrites arising directly from the cell's soma. These cells occur in certain ganglia of the autonomic nervous system of vertebrates."

Found this online...though it doesn't seem right, or at least complete somehow....

Got me Doc. It seems like I was told, but I can't remember now....

Dwayne

[AnthonyM83]

10 points for anyone that can say which neurons do not have dendrites.

Will you take: What is heart muscle? Heard it compared to neurons in its electrical conduction abilities