 Do you know that the human heart continues to beat even if you take it out of the human body? Yes, it does and it is because the beating of the heart is not dependent on any other body part. It can beat on its own and so it is called myogenic heart myogenic Myogenic simply means that the impulse for the heart to beat originates in the muscles of the heart itself But it's not that the whole of the heart or the entire cardiac muscles are capable of doing it Capable of creating an impulse. It's just certain parts here and there which gets modified and we call them nodal tissues Well, the meaning of the word nodal simply means a mass of tissue that that got differentiated Okay, here the cardiac muscle in certain places it gets modified it it differentiates into a kind of tissue that can Originate impulse on its own Therefore we call it the nodal tissue and the heart is called the myogenic heart because the impulse is not coming from any Other part of the body, but from the heart itself Okay, now let's have a look at where these nodal tissues are located in the heart and for that we have a diagram of human Heart, we know this is the right atrium left atrium right ventricle and the left ventricle and from the previous videos We already know how the blood runs in and out from the heart, right? Now talking about the nodal tissues the first and the most powerful one is located in the right atrium and to be precise it is present at the junction between the right atrium and the Superior vena cava that is bringing in the deoxygenated blood into the right atrium and this nodal tissue is called The SA node or the Sino atrial node now Can you guess how many times will this SA node create an impulse per minute? Well, the capacity of SA node is to produce hundred impulse per minute and And and and our heart can actually beat hundred times per minute But it is seen that the normal heart rate or the normal heartbeat is just 70 to 75 times per minute and The reason behind this is the inhibitory effect of the vagus nerve so there's a special nerve called vagus nerve that release certain neurotransmitters onto the SA node and regulates its heartbeat to just 70 to 75 beats per minute and That is how fast our heart beats that is the pace of our heart, right? And therefore the SA node is also called the pacemaker of the heart or we also call this the heart rhythm So the rhythmicity of the heart is also maintained by the SA node Okay, now can you tell me what would happen if I cut off the vagus nerve? This connect the SA node with the vagus nerve. Will there be any change in the heart rate? Well, it will increase right because the SA node otherwise has the capacity to generate hundred impulses per minute Okay, now talking about the impulse of the SA node is the impulse from the SA node sufficient to contract the whole heart Well, it is seen that the impulses are restricted only to the two atria It cannot move down to the ventricles due to the presence of the fibrous Non-conducting tissue between the atria and the ventricles Therefore to bring the impulse down into the ventricles We have another nodal tissue at the lower left corner of the atrium right atrium We call it the AV node atrio ventricular node and it is called so because it is present at the junction between the atrium and the ventricle Right, that's why it is called the atrio ventricular node and it brings the impulse down into the into the ventricles But apart from that AV node itself can generate its own impulse because it's it's also a nodal tissue, right? So it can generate 60 to 65 impulse per minute So even if the SA node sometimes is not functional then AV node can can generate enough impulse 60 to 65 times per minute now this AV node is extended downward like a bundle and This portion or this part of the nodal tissue is given a different name. It is called the bundle of his And it is given after the name of the scientist who first discovered it It is nothing but a part of the nodal tissue that is also helping in the conduction of this impulse from the AV node down to to the ventricles Okay, and as you can see its position is in the intra ventricular septum And again being a nodal tissue. It can also generate its own impulse. It can generate up to 45 impulse per minute Now the bundle of his in order to reach both the ventricles properly it bifurcates into two separate bundles And each bundle as you can see it forms a branches branches and It seems as if it is holding the two ventricles and this part Is called the parking fiber. This again is a nodal tissue and just like other nodal tissue It can also generate its own impulse even though very less, which is 20 to 25 impulses per minute Even though it is less, but it has the capacity to generate its own impulse. Okay And these fibers are superb for conducting the heartbeat down into the ventricles in a synchronized manner Okay, and again talking about the name parkinji. It is named after the scientist who discovered it All right, okay now if you carefully look at the diagram You will notice that the left ventricle has more parking fiber covering than the than the right one Now can you think of a reason behind this uneven distribution of parking fibers? Well, the reason is that the right ventricle has to push out blood only to the lungs Okay, which is not very far Okay, so a small contraction a small part of the impulse does the work but for the Left ventricle it pushes blood out of the heart to all different parts of your body to the tip of your toe as well And that calls for a very forceful contraction in the left ventricle And that's the reason we see more parking fiber towards the left So these are the four nodal tissues that work pretty much like the wiring system at our homes The electrical wiring system, right? They are the wiring system of our heart And our tiny little heart is able to pump blood to each and every cell of our body only and only because Of this magical wiring system that we have made of nodal tissues that conducts impulses all throughout the heart