Neurotransmitters of the ANS - Online Tutor, Practice Problems & Exam Prep

The autonomic nervous system (ANS) utilizes three key neurotransmitters: acetylcholine, norepinephrine, and epinephrine. Preganglionic fibers in both sympathetic and parasympathetic divisions release acetylcholine, while sympathetic postganglionic fibers primarily release norepinephrine. Cholinergic receptors, including nicotinic and muscarinic types, respond to acetylcholine, while adrenergic receptors bind norepinephrine and epinephrine. Understanding these neurotransmitters and their receptors is crucial for grasping the physiological responses of the body, particularly in stress and relaxation scenarios.

Neurotransmitters of the ANS

Hey, everyone. So, now we're going to dive into the neurotransmitters of our autonomic nervous system. Our ANS uses three neurotransmitters: acetylcholine, norepinephrine, and epinephrine. You can see we have this table here, organized by division as well as pre and postganglionic, so you can see what type of neurotransmitter each of these fibers will be releasing.

So, if we start with the sympathetic division, you can see that our preganglionic fibers will be releasing acetylcholine, and then our postganglionic fibers will be mostly releasing norepinephrine, also known as noradrenaline. When I say 'mostly', I mean about 80% of these fibers release this neurotransmitter, so this really is like the main neurotransmitter of this division. However, some of these fibers do release epinephrine, also known as adrenaline, and a few release acetylcholine, although that is fairly rare, so just keep that in mind. Norepinephrine is really kind of the big one.

And then in our parasympathetic division, this one's kind of easy because both the pre and postganglionic fibers just release acetylcholine. So, when we're talking about these fibers, we're going to be referring to them as cholinergic and adrenergic. A cholinergic fiber is a fiber that releases acetylcholine, which, as I'm sure you can see based on our table, the majority of our fibers are going to be cholinergic fibers. Cholinergic fibers include our sympathetic preganglionic fibers, they include our parasympathetic preganglionic fibers, as well as our parasympathetic postganglionic fibers.

I want to draw your attention to two things here. The first is that the entire parasympathetic division is represented here. So, all parasympathetic fibers are cholinergic fibers. They all release acetylcholine. And also worth noting is that all of our preganglionic fibers are represented here. Within our autonomic nervous system, all preganglionic fibers are cholinergic. They all release acetylcholine. You can kind of think of cholinergic fibers as being kind of like the default fiber of our ANS.

Then there's this one kind of pesky exception to that, which are these adrenergic fibers, which release norepinephrine and epinephrine. These are going to be our sympathetic postganglionic fibers. Cholinergic is kind of our default, and then adrenergic is kind of the exception. So, if we look at our image here, we have our sympathetic nervous system over here and our parasympathetic nervous system here with the yellow. And you can see, like we talked about, the majority of these fibers are red. They are mostly cholinergic. That's our default fiber. So you can see our entire parasympathetic division is represented here. Both the pre and postganglionic fibers here are all going to be cholinergic, and then you can see over on our sympathetic side all of those preganglionic fibers are cholinergic as well.

Then we have this exception here, these blue fibers, these adrenergic fibers. This exception is actually fairly intuitive when you think about it, as these are the fibers that are directly connecting our sympathetic division to our organs. So, it makes sense for them to be dumping adrenaline and noradrenaline onto those organs because that is what is going to create that fight or flight response. And so, you can see why we would want these blue fibers over here on the sympathetic side, getting that fight or flight response going, and we would not want any blue fibers anywhere else. We want to contain that epinephrine and norepinephrine and only use it when it's necessary. So, that is why we have those blue fibers there on our sympathetic side.

Alright. So that is our intro to neurotransmitters, and I will see you guys in our next video. Bye-bye.

Neurotransmitters of the ANS Example 1

Okay. So for this one, we have this lovely depiction of dual innervation of the heart and we're going to be going through and labeling if these fibers are cholinergic, releasing acetylcholine, or adrenergic releasing norepinephrine or epinephrine. So, starting here in our sympathetic division with this preganglionic fiber, remember all preganglionic fibers in our entire autonomic nervous system are always going to be cholinergic, so it has to be a cholinergic fiber. And then you know what? While we're at it, let's go ahead and label this preganglionic fiber here on the parasympathetic side as well because it also has to be cholinergic. Alright.

So now jumping over here to the postganglionic fiber on the sympathetic side. This is going to be the fiber that is directly communicating with the effector organs. And to get that sympathetic activation, that fight or flight response going, we want to be putting some adrenaline into our system. So, this is going to be an adrenergic fiber. Then, scooching over here to the postganglionic fiber on our parasympathetic side now, this is our rest and digest. Right? So this does not want to be pumping any adrenaline into our body. This is going to be a cholinergic fiber as well. And you can see on our parasympathetic side both of our fibers are going to be cholinergic. So, it's pretty easy to remember that. So, really, just the one that's different is going to be that postganglionic sympathetic fiber, and that's going to be an adrenergic fiber.

Alright. So, there you have it, and I'll see you in the next one. Bye-bye.

___________ and ___________ are the major neurotransmitters released by autonomic nervous system neurons.

• A. Nicotine; muscarine.
• B. Acetylcholine; norepinephrine.
• C. Acetylcholine; serotonin.
• D. Noradrenaline; adenosine.

The neurotransmitter released at all synapses in the parasympathetic division is:

• A. Serotonin.
• B. Norepinephrine.
• C. Epinephrine.
• D. Acetylcholine.

Neurotransmitter Receptors

Alright. So now we're going to dive into neurotransmitter receptors. So neurotransmitter receptors are just membrane receptors that are activated by neurotransmitters, and we can classify these receptors based on the neurotransmitter that they bind to. And within our ANS, there are two main types of neurotransmitter receptors. We have adrenergic receptors, which bind to norepinephrine and epinephrine, and we have cholinergic receptors, which bind to acetylcholine. Now, one very important subtype of cholinergic receptor is a nicotinic receptor. So, again, this is a subtype of cholinergic receptor; it's going to be responding to acetylcholine, and these are highly abundant within our ANS. In fact, these are located at every synapse between pre- and postganglionic fibers within the entire autonomic nervous system. Notably, these are also located in the adrenal medulla, which you guys remember is that sympathetic structure located within the adrenal gland, and this structure is responsible for releasing epinephrine and norepinephrine. So, if we look down at our image here, just to kind of orient you, we have our sympathetic division here on the left and our parasympathetic division here on the right. And you can see we have these little colored circles on each of our receptor sites. And you can see how some of them are grayed out, no spoilers; those are for a future video, but then looking here at all the ones in green, those are all going to be our nicotinic receptors. So you can see how we have these nicotinic receptors present again at literally every single preganglionic postganglionic synapse within our entire ANS. And that makes sense. Right? Because remember, these receptors respond to acetylcholine, and all of our preganglionic fibers, again sympathetic and parasympathetic, all those preganglionic fibers are all cholinergic, so they're all going to be releasing acetylcholine. So we have to have that receptor site that can, of course, bind to acetylcholine. So those are our nicotinic receptors, one of the most abundant types of neurotransmitter receptors within our entire ANS. And I will see you guys in our next video to finish up talking about neurotransmitters. Bye bye.

Neurotransmitters of the ANS Example 2

Alright. So this one asks where you would find a cholinergic nicotinic receptor? As a reminder, cholinergic receptors respond to acetylcholine, which is released by all preganglionic fibers in the entire autonomic nervous system. So, we're going to have those nicotinic receptors at the synapse between all preganglionic and postganglionic fibers, again, in the entire ANS, both sympathetic and parasympathetic. So based on that, our answer here is going to be d.

Looking quickly at a through c, so a reads at a parasympathetic effector, and those are going to have cholinergic receptors, but they're not going to be nicotinic. We're actually going to have a video on that coming up, so stay tuned for that. Alright, and then c reads at a sympathetic effector, but those are going to be working with epinephrine and norepinephrine, so those need adrenergic receptors, right?

And then b) it's kind of a trick question because we don't have synapses between two preganglionic fibers, right? We synapse between a preganglionic and a postganglionic fiber. So our answer here is d, and there you go.

Receptors at Target Organs

Going to finish up this section by talking about a few more types of neurotransmitter receptors. So we're going to begin with muscarinic receptors. Now these are another type of cholinergic receptors so they respond to acetylcholine and these can be found at all parasympathetic target organs. And these are also present in the sympathetic system, but they're really only present at sweat glands. So they're not particularly prominent in that sympathetic division. They are really prominent in that parasympathetic system. And then we have our adrenergic receptors that respond, of course, to norepinephrine and epinephrine. And these will be very commonly found at sympathetic target organs and we'll see that in the image in just one second.

Now there are two subtypes of adrenergic receptors. We have alpha receptors and beta receptors and there are subtypes of alpha and beta receptors as well. We're not going to cover that in detail in this video but do make sure that you are aware of what your professor wants you to know.

So, scooching down to our image, you can see we have all of these receptor sites. All these synapses now have highlights. We still have all of those green highlights; those are our nicotinic receptors. You can see that those are present at all the synapses between pre and postganglionic neurons there. And we're going to start over here on the parasympathetic side looking at all of these yellow highlighted receptor sites and those are going to be where our muscarinic receptors are present. So remember, those are a type of cholinergic receptor; they're going to be responding to acetylcholine and of course that makes sense because we have all of these little postganglionic cholinergic fibers there that will be releasing acetylcholine into those synapses. So you can see all of our target organs on that parasympathetic side have those muscarinic receptors there in yellow.

Looking at our sympathetic side, you can see we have these pinkish purple highlights on most of our sympathetic target organs and those are going to be our adrenergic receptors. And you can see we do have a couple of exceptions here. You can see on the skin we have that muscarinic receptor and then down here on the adrenal medulla we have that nicotinic receptor like we talked about last time. You can see how the majority of these are going to be adrenergic and, of course, that makes sense because all of these adrenergic fibers, all these postganglionic adrenergic fibers, are going to be releasing norepinephrine and epinephrine, so those target organs have to have receptors that can bind to those neurotransmitters.

Alright. So that is our section on neurotransmitters and I will see you guys in our next video. Bye bye.

Neurotransmitters of the ANS Example 3

Okay. It looks like for this one we're going to be filling in the blanks using the terms cholinergic, adrenergic, nicotinic, muscarinic, beta, increased, and decreased. So let's start here with our sympathetic activity up top. So first, we have our preganglionic fiber and that is going to be a cholinergic fiber, right? All of our preganglionic fibers in the entire autonomic nervous system are cholinergic. They all release acetylcholine. So that's going to be a cholinergic fiber. And we can see that it is indeed releasing acetylcholine there, and then we're going to have our receptor right here. Remember, all of the receptors between our preganglionic and postganglionic fibers in the entire autonomic nervous system are nicotinic, so that has to be a nicotinic receptor. That's a subtype of a cholinergic receptor. So that is our nicotinic receptor. Alright, and then we have our postganglionic fiber. Now in our sympathetic division, remember, we want to be getting those organs some adrenaline, right? Adrenaline or noradrenaline, and we can see that this one here is indeed releasing norepinephrine or noradrenaline so this has to be an adrenergic fiber. Okay. So that's our adrenergic fiber. It's releasing some noradrenaline, and then we have this receptor here, and in this case, this receptor is going to be a beta receptor. Remember, that is a subtype of adrenergic receptor, and we see those on our sympathetic target organs. So we're going to put beta here and here we are innervating the heart, it looks like, and so with our sympathetic activity, we're going to have an increased heart rate. Alright, so let's scooch down to our parasympathetic activity and we'll do the same thing. So like we said, all of our preganglionic fibers in the entire ANS are cholinergic and this one is no exception. We can see it releasing acetylcholine there. So that is a cholinergic fiber. Alright. And then we have that nicotinic receptor. Same thing, right? All of our synapses between pre and postganglionic fibers always have those nicotinic receptors. Alright. And then in our parasympathetic division, that postganglionic fiber is also going to be cholinergic. We can see it releasing acetylcholine here. That is a cholinergic fiber. Remember, we would not want to be releasing any adrenaline or noradrenaline in this parasympathetic division, right? That would be very counterproductive. And then we have this receptor here, and that is going to be a type of cholinergic receptor. This is going to be our muscarinic receptor. Remember, these muscarinic receptors are found at all of our parasympathetic target organs. And so here, with our parasympathetic activity, we're going to have a decreased heart rate. Alright, so there you go. That is kind of a nice run-through of how we would label all of these fibers and all of these receptors, and I will see you guys in our next video. Bye bye.

What are the two types of receptors found in the parasympathetic system?

• A. Cholinergic and adrenergic.
• B. Nicotinic and muscarinic.
• C. Nicotinic and alpha receptors.
• D. Muscarinic and beta receptors.

Here’s what students ask on this topic:

What are the main neurotransmitters of the autonomic nervous system (ANS)?

The autonomic nervous system (ANS) primarily uses three neurotransmitters: acetylcholine, norepinephrine, and epinephrine. Preganglionic fibers in both the sympathetic and parasympathetic divisions release acetylcholine. Sympathetic postganglionic fibers mainly release norepinephrine, with some also releasing epinephrine. Acetylcholine is the neurotransmitter for all parasympathetic postganglionic fibers. Understanding these neurotransmitters is crucial for grasping how the ANS regulates bodily functions, particularly in stress (sympathetic) and relaxation (parasympathetic) scenarios.

What are cholinergic and adrenergic fibers in the ANS?

Cholinergic fibers in the ANS release acetylcholine. These include all preganglionic fibers (both sympathetic and parasympathetic) and parasympathetic postganglionic fibers. Adrenergic fibers release norepinephrine and epinephrine and are primarily found in sympathetic postganglionic fibers. Cholinergic fibers are the default in the ANS, while adrenergic fibers are specialized for the sympathetic division, particularly in initiating the fight-or-flight response.

What are the types of cholinergic receptors in the ANS?

Cholinergic receptors in the ANS are classified into two main types: nicotinic and muscarinic receptors. Nicotinic receptors are found at all synapses between preganglionic and postganglionic fibers in both the sympathetic and parasympathetic divisions. Muscarinic receptors are located at all parasympathetic target organs and at sweat glands in the sympathetic division. Both types respond to acetylcholine, but they are distributed differently within the ANS.

What are adrenergic receptors and where are they found in the ANS?

Adrenergic receptors in the ANS respond to norepinephrine and epinephrine. They are primarily found at sympathetic target organs. There are two main subtypes of adrenergic receptors: alpha and beta receptors, each with further subtypes. These receptors are crucial for mediating the effects of the sympathetic nervous system, such as increasing heart rate and dilating airways during the fight-or-flight response.

How do nicotinic receptors function in the ANS?

Nicotinic receptors are a subtype of cholinergic receptors that respond to acetylcholine. They are located at every synapse between preganglionic and postganglionic fibers in both the sympathetic and parasympathetic divisions of the ANS. These receptors are also found in the adrenal medulla, which releases epinephrine and norepinephrine. Nicotinic receptors play a crucial role in transmitting signals within the ANS, ensuring proper communication between neurons.