the heart beats in response to electrical signals we call action potentials. We'll learn more about these in the chapter on the nervous system. For now, just know that these air electrical signals that air generated by moving ion cross the membrane of cells. Now action potentials in the heart are not transmitted by nerves like we'll see throughout the nervous system. These action potentials actually move between the cells of the heart through what are called gap junctions. Gap junctions, which you can see right here have are basically direct cell to cell connections. And there are these channels between the cells that ions can flow through these channels, air referred to as connections. You don't need to worry about memorizing any of this. Just know that the action potentials in heart cells are moving cell to cell through gap junctions. In fact, there's actually a specialized structure in heart muscle that connects neighboring cells and contains these gap junctions. We call those inter Kalay tid disks and here is an example of some heart tissue, and if you zoom in, you can see some inter Kalay tid disks between the cells. Now here we actually have a recording of an action potential. And hopefully this looks a little familiar to you, right? That blue, blue, blue, That line that you see on the heart, the heart rate monitor, right? The thing in the hospital that we just looked at it looks a heck of a lot like that, right? It is, in fact, measuring what is known as a, uh, the electric potential. Something measured in volts. It's a type of voltage. You don't need to worry about remembering any of this. I just want you to see the similarity between this standard image of an action potential and what we see appear on the heart rate monitor because they're, uh, you know, basically measuring. You know the same thing. Now, how do these action potentials get generated? Well, there is a special part of the heart, a group of cells in the right atrium that are referred to as the Sino atrial node. And basically, these cells are going to be responsible for initiating heart contractions, invertebrates. There's actually a group of cells there that air usually referred to as pacemaker cells, and these air thesis cells that will control the rate and timing of heartbeats and they are going to actually start, Uh, the action potential. They're going to be the initiator of the action potential? No, from the s a node, as it's often referred to, the action potential is going to propagate to what's called the a trio ventricular node, which is a group of cells that is sort of it's almost like the center of the heart. You can see the A V node being pointed out here. So our s a node was up here. The action potential moves down to the A V node and at the A V nodes, something interesting happens. See that signal? That electrical signal is delayed, and the reason for that is we want the atria to have a little extra time to completely empty its blood into the ventricles. So by having a slight delay in the signal at the A V node before it moves down into the ventricles, we actually give the atria at the time. It needs Teoh. You know, push all the blood has out into the ventricles, making the work of the ventricles contraction more efficient. No, When the signal goes down into the ventricles, something kind of interesting happens. So from the A V note, it actually goes down to basically like the bottom of the ventricles. And from there it's propagated up through the ventricles through these five fibers called perkin gee fibers Perkin E fibers. You may hear it pronounced, depending on whether you give it a softer, hard J. Anyhow, these Perkin gee fibers will actually spread the action potential up through the ventricles from the bottom to the top. Now, the reason for this is the arteries have their openings located kind of at the top of the ventricles. Use a different color here, make these arteries like red. So by having the ventricles start there, contraction from the bottom and move it up. You're actually pushing the blood up into these arteries. That's the reason for it. Now, this whole process, this whole electrical process is recorded in what's called an electrocardiogram. Sometimes it's abbreviated, E k g. If you're wondering why it's not e k c e k g comes from the German word. Uh, so, you know, kind of confusing there, but it's the same thing E K g is an electrocardiogram. So this is going to record the electrical activity of the heart and it's going to be output looking like this. So at the start here we have our s a node that is going to lead R s. A note is going to initiate theatrics in potential. This is going to be the big contraction of the ventricles. And here we have relax ation of the muscles so you don't need to worry about memorizing the different parts of the E k. G Signal. Just wanted to sort of show you how these electrical signals correspond to the phenomena that we've just been talking about. So with that, let's actually flip the page.