the electrocardiogram we see it in hospitals all the time but how do you read it what do the parts of the graph mean I promise that by the end of this video you'll get it so let's do it [Music] [Applause] let's see someone here from interactive biology where we're making biology fun and let's talk about the electrocardiogram the EKG or ECG for short an electrocardiogram is a test that records the electrical activity of the heart now in a previous video we looked at how the signals of the heartbeat are generated and for A Brief Review the signal for the heart to contract it starts with the SA node in the right atrium that signal then spreads throughout the Atria causing them to contract then the signal reaches the AV node which then goes via the bundle fibers all the way to the purkinje fibers sending that signal throughout the ventricles for the ventricles to contract now if that sounds confusing don't worry I'll link to my video about that in the description for you to check it out for now let's continue with the EKG we use the EKG to test for irregularities and how the heart is functioning you've probably either seen this firsthand in a hospital or maybe even on TV but you can look at the electrocardiogram and it will tell you if if the electrical activity of the heart is working the way it should now the way we do this is by placing skin electrodes on different parts of the body and these electrodes are able to record the electrical activity of the heart and the result is that it gives you a graph that looks like this there's normally a beep associated with it so let's add that in yep that's the beep now what I want to do is look at each component of the electrocardiogram and break it down cool all right let's do it the first thing we see is this little bump on the graph this is called the P wave then we have this structure here called the QRS complex and lastly we have another little bump called the T wave let's start by looking at the P wave as a reminder once the SA node generates that signal the signal then spreads to the muscle cells in the left and right Atria this is because of a unique characteristic of cardiac muscle cells in that they are all electrically connected to the muscle cells around them so if you get a signal in one it'll spread to the rest it's all or nothing and once that signal spreads throughout the Atria that electrical activity is recorded on the EKG as the P wave that's the first structure we see and it represents the spread of the electrical signal throughout the Atria or the depolarization of the Atria now going back to what we know about how that that signal spreads it then goes to the AV node and then that signal spreads throughout the rest of the fibers to the ventricles and as that signal spreads through the ventricles that's shown in the EKG as the QRS complex so the QRS complex shows us the depolarization of the ventricles now you'll notice that the QRS complex is significantly larger than the P wave why is this well if you look at the structure of the heart what you're going to see is that the ventricles are significantly larger than the Atria there's a lot more muscle there now this makes sense because while the Atria they only have to pump blood right next door to the ventricles those ventricles are responsible for pumping the blood all throughout the body so they need more muscle and as a result the signal that we see is going to be larger than the signal from the Atria it makes sense lastly we have the T wave now after depolarization we have repolarization and in this case when the ventricles repolarize we see this structure right here the T wave and as a reminder first depolarization happens which then causes contraction then repolarization happen which causes relaxation okay so you're probably wondering why we don't see the repolarization of the Atria and the EKG well it does happen but here's the thing the repolarization of the Atria happens while the ventricles are depolarizing so it gets overshadowed by the much larger QRS complex and we don't see it on the graph so we have the P wave representing atrial depolarization then the QRS complex representing ventricular depolarization and the T wave representing ventricular repolarization and that's the electrocardiogram the EKG but don't stop here I mean you gotta understand how those electrical signals results in actual contraction of the heart and that's what I talk about in this next video so click over there and check it out