Select Page

046 How Adrenaline and Acetylcholine Affect Heart Rate

In this episode, Leslie discusses the effect of adrenaline and acetylcholine on heart rate. These two modifies the conductance of the ions across the membranes of the cells of the SA node causing either an increase or a decrease in heart rate.

Watch and learn how it all works.


Transcript of Today’s Episode

Hello and welcome to another episode of Interactive Biology TV where we’re making Biology fun. My name is Leslie Samuel and in this episode, Episode 46, I’m going to talk about how adrenaline and acetylcholine affect heart rate. So, let’s get right into it.

In the last episode, Episode 45, we looked at this slide where I showed that in the SA node, we have a pacemaker potential that results in a spontaneous signal so that we have the heart beating in response to these action potentials that are automatically generated in the SA node.

If you haven’t looked at Episode 45, I would recommend for you to pause this right now and go and watch Episode 45 so that you’re going to get a full understanding of what we’re going to be talking about.

Let’s go to the next slide. I’m sure you’ve all been in situations where, let’s say you’re doing something and someone jumps up behind you and scares you. What happens? Your heart starts beating faster. The reason it starts beating faster is because adrenaline is released from the adrenal gland that’s located above the kidneys. When that adrenaline is released, that causes the conductance in the pacemaker cells to change. As you can see here, we have an increased conductance for sodium and calcium ions. That is going to cause those to rush into the cell much faster.

It’s going to look a little different than what we looked at before because the membrane potential is going to increase significantly faster so that we’re going to get a faster action potential. So, it might look something like this. As you can see, the signal happens much faster. Forgive my sloppy drawing here. So, we have signals being produced much faster and the heart rate increases. If you remember from the last one that I showed, I was able to show two action potentials on this. But, because sodium and calcium ions are rushing in much faster, the signals are going to be generated much faster because it’s going to reach the threshold much faster and we get an increased heart rate. So, that’s adrenaline.

Now, there’s an opposite effect where instead of adrenaline being released, we have acetylcholine being released. I didn’t plan for the acetylcholine to come in as a flame but, it did for some reason.

What happens when acetylcholine is released? As you can see up here, the conductance for potassium is going to increase significantly. You should know that potassium wants to leave the cell. So, this is going to increase hyperpolarization and is going to slow down depolarization.

What’s going to happen is, instead of this rapid depolarization, we’re going to get a significantly slower depolarization so that, it takes much longer to reach the threshold. When it reaches the threshold, the usual process happens: voltage-gated calcium channels open and calcium rushes in to the cell. Then, we have our depolarization. Then, this process continues.

But, as you can see here, depolarization is much slower than over here. Here, depolarization is sped up because sodium and calcium are rushing into the cell much faster in response to adrenaline. Here, it’s going to be much slower because more potassium is leaving the cell causing depolarization to slow down and we get a slower heart rate.

Faster heart rate in response to adrenaline; slower heart rate in response to acetylcholine.

That’s pretty much it for this video. As usual, you can visit the website at for more Biology videos and all of the other resources we’re putting together over there. This is Leslie Samuel. That’s it for this video and I’ll see you on the next one.

About The Author

Leslie Samuel

Leslie Samuel is the creator of Interactive Biology. His mission is to use this site to Make Biology fun for people all over the world.