In this episode, Leslie talks about how a pacemaker potential can cause a heart to beat automatically. Details about how it is generated is discussed in this video. Just how does this happen, our heart beating again and again?
Watch to learn more. Have fun and enjoy!
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 45, I’m going to be talking about the pacemaker potential of the S.A. node and the A.V. node. We’re basically going to look at how this results in the heart beating automatically. So, let’s get right into it.
Let’s first talk about the S.A. node. The S.A. node stands for the sinoatrial node and you can see it in this figure over here, it is number one. That’s this cluster of cells. It is basically a specialized group of cardiac muscle cells that don’t contract which is kind of strange. They’re muscle cells and they don’t actually contract.
But, what’s special about these cells is that they are adapted to automatically generate impulses. So, it can automatically cause signals that can spread throughout the heart, causing the heart to beat. The S.A. node functions as the pacemaker of the heart. Yes, we have the A.V. node and some other stuff that we are going to talk about but, these generates signals faster than any of the others so, it sets the pace for the heartbeat.
As you can see, it is located in the right atrium. So, now let’s talk about the A.V. node.
The A.V. node is number two. So, it’s this cluster of cells here and it stands for the atrioventricular node. It is similar in function to the S.A. node in that it automatically generates impulses and it is located between the atria and the ventricles hence the name, atrioventricular node. Let’s go back to the S.A. node and see how this results in the pacemaker potential.
Before we look at that, I just want to point out that we have, in addition to the S.A. node and the A.V. node, we have some fibers that extend from the A.V. node and spread throughout the ventricle and those fibers are called Purkinje fibers. These are also very important in that they spread that signal throughout the rest of the ventricle. Let’s talk about the S.A node.
We said that that functions as a pacemaker. So, we are going to look at the pacemaker cells that we have in the S.A. node. What is special about these cells is that normally, there’s a significantly higher conductance for sodium than there is for potassium. Now, if you go back to Episode 006, I talk about Donnan equilibrium and driving force and I show how there’s normally a driving force for sodium to rush into the cell. I also show that potassium wants to leave the cell.
Because the cell is much more permeable to sodium, we’re going to have a situation where there’s much more sodium coming in than potassium leaving. Because we have more positives going in than leaving, what we’re going to get is a pacemaker potential where the cell normally depolarizes. Then, when it reaches the threshold, something interesting happens. Yes, we have the sodium rushing in and some potassium leaving but, now that we’ve reached the threshold, voltage-gated calcium channels open and calcium is going to rush into the cell.
So, we’re going to get this rapid depolarization. In other words, we’re going to get an action potential. At the peak, we’re going to get a different situation where, yes, we have sodium coming in and potassium leaving but, voltage-gated potassium channels are going to open so that the conductance for potassium increases significantly and potassium is going to rush out of the cell repolarizing the membrane.
At that point, we still have the sodium that’s coming in and the voltage-gated potassium channels close so, we have the initial situation where sodium is rushing into the cell, causing this depolarization then, the same thing happens. It reaches the threshold, voltage-gated calcium channels open depolarizing the cell membrane once again, causing that impulse. Voltage-gated potassium channels open causing potassium to rush out of the cell again.
This process continues over and over and over. What ends up happening is we have this automatic signal that’s generated constantly resulting in the contraction of the heart. This causes the heart to beat. It’s really that straightforward but, the main idea is that the cells in the S.A. node have a significantly higher conductance for sodium so it continuously depolarizes causing that impulse that causes the heart to beat.
That’s really all I want to talk about in this video. As usual, you can visit the website at Interactive-Biology.com for more Biology videos and other resources to help make Biology fun.
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. He created this site to help Make Biology Fun and has the goal of making this the biggest and best biology resource on the net.
all these videos are great. thank you!
[Reply]
So amazing
[Reply]
biology will never be fun…NEVER.
[Reply]
THANK YOU
oh this helps me visually . I could not understand what contraction meant (i speak a different language) but seeing the first part now this really helps more than the text book and the lecture audio from my instructor
[Reply]
wow u are amazing!!!!!!! than you from those of us who have bad teachers!!
[Reply]
purkyne tissue he said purkingy fibres ?
[Reply]
simple, concise and easy to understand. Very helpful, thank you Leslie
[Reply]
Very informative and to the point. Thank you
[Reply]
You did a great job. Very very useful.
[Reply]
tnx we need more like u thanks so muchhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh so clearrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr
[Reply]
Very helpful!! Thank you!
[Reply]
A great vedio .. thanks sir (lub-dup:))
[Reply]
Great Video! Definitely helpful, thanks for posting
[Reply]
Amazing videos. Thank you so much. Making my classes so much easier to understand!
[Reply]
thank you soo much for this heart series as i’m really bad at it as my mock proved
[Reply]
Thanks so much for putting this up. Appreciate it so much. Bless you.
[Reply]
I like your vdo very much
[Reply]
Thank you. You just saved me a possible 40 minutes trying to figure out what my textbook is trying to tell me haha, 20 minutes of aimlessly staring into the pages and another 20 trying to read half latin/greek derived words. You display complex effects in simple terms and still manage to include all the crucial information.
[Reply]
Thank you so much for this explanation. This has been tremendously helpful and I cannot thank you enough!
[Reply]
Thank you!! You made it so easy to understand!
[Reply]
You are amazing!!!. Do you have any videos in which you explain the blood types and Rh factor?.
[Reply]
i have an exam tomorrow and this is great!
[Reply]
it helped me alot thank you!!!!!
u explain it very well 
[Reply]
Thx very much it’s really helpful
[Reply]
perfect! thanks for this effort.
[Reply]
thankxx
[Reply]
lol
[Reply]
Very informative I love your videos, Keep them up
[Reply]
Another helpful video! Thank you!!
[Reply]
Doesn’t the influx of calcium followed by the opening of voltage gated K channels result in a plateau ? I’m really confused – please help!
[Reply]
This is like a skeletal muscles A.P?. Im a little confused my teacher was talking about funny channels, where does that come into the picture?
[Reply]
There are two types of cardiac muscles: contractile muscle cells and autorhythmic muscle cells. Contractile cells make up 90% of muscle cells in the heart and autorhythmic cells make up 10% in the nodes. Autorhythmic muscle cells start the action potentials from the SA and AV nodes that disseminate into contractile cells causing them to contract. InteractiveBiology described the action potential of autorhythmic cells, you described contractile cells. Hope this helped
[Reply]
thank you so much for posting these videos, they’re all very very helpful
[Reply]
You are an awesome individual to take the time to put all these videos. And you make it so simple and easy to understand without getting lost. Thanks MUCH!!
[Reply]
I just love how this particular person gives free lectures plus all the interactive are very easy for me to understand..keep up the good work leslie! You’re making everyone’s life easier
[Reply]
yes that’s right.. because of the equilibrium
[Reply]
I never understood this fully before, but you make things that much easier to understand. I can’t thank you enough!!!
[Reply]
where´s the funny channel ? xD
[Reply]
thank you so much that was a great help ^^
[Reply]