the cardiac conduction system otherwise known as the nodal system because of things like the sinoatrial node which is why they call it that so we do not have to do this in lab so the list there under components is something you're only responsible for in lecture so although we will look at some diagrams don't don't worry about trying to find that on a picture so this is a pretty important part of the heart because this is how the heart sends its signal throughout so basically it's not good if one part of your heart is beating at a different rhythm than the other and so this is how you control that just to make sure everybody's on the same team so this is specialized muscle tissue and so there's a key point there specialized muscle tissue it's not nerve even though it's gonna kind of look like nervous tissue it's not actually nerve so basically this is tissue that is able to conduct depolarization waves so if you remember from a t1 it's been a while depolarization was when this cell became less negative it was used for muscle contraction it was basically when the sodium was rushing in so this is basically depolarization is basically a term for sending the muscle contraction signal so we've got to send those waves throughout the entire muscle wall throughout the entire myocardium so this is done by the sinoatrial node the junctional fibers the atrioventricular node and atrioventricular bundle bundle branches and these things called so starting with the sinoatrial node or the SA node it's also called the pacemaker but don't get that confused with when they artificially put a pacemaker in yourself we just happened to call this part of the heart wall the pacemaker because he's the one setting the pace it's kind of like in a car race you have the car that sets the fastest pace so we call them the pacemaker so these are special heart cells again they're gonna look a lot like nerve tissue these are special heart cells that are going to depolarize faster kind of contract faster than any other heart fibers so this is where your cardiac cycle begins this is where the heartbeat begins is in this pacemaker so the fastest one sets the pace it's usually the SA node but it doesn't always have to be as we're about to see so this sends a signal generally about 60 to 80 times per minute because generally your heart beats 60 to 80 times per minute right so anatomically it's in your right upper atrial wall near where the superior vena cava merges with the heart so will your heart always be 60 to 80 beats per minute of course not it's perfectly normal sometimes to have a lower heart rate it can be even perfectly normal to have a higher one what we would call resting heart rate when you're just sitting there listening to me trying to stay awake right but of course if you're exercising it's gonna go up if you're scared it's gonna go up if you're sleeping it's gonna go down so even though the SA node is there to initiate the signal it can be faster or slower so the heart rate can be increased by your sympathetic nervous system say a lion tiger bear oh my is chasing you that's gonna speed up your heart rate say your adrenaline starts pumping because a deer runs out in front of you again that's going to increase your heart rate so if the heart starts beating really really crazy you're ultimately your brain through the vagus nerve which was cranial nerve number 10 from a mp1 can it's kind of put the brakes on your heart so although the heart is very self-regulating the heart sets its own pace ultimately the brain can override that I mean the brain is in charge of everything right so if you're going too crazy we're gonna put the put the brakes on we also have these structures called junctional fibers special muscle cells yet again even though if you look at this little bottom picture on the bottom side or bottom right hand side there it looks like nervous tissue so special muscle again that is able to send that signal and so if you look in the picture especially I think the next one I haves a little bit better we're trying to stimulate both atria at the same time so the SA node is sitting there we need to tell both atria to contract at exactly the same time so these junctional fibers are able to spread that message just like if I said sent an email to everyone in blackboard that you would all get it you wouldn't maybe necessarily get it at the same time but I sent it at the exact same time so the signal is traveling at the exact same time then there's other junctional fibers that carry the signal to the next step which is the AV node so the atrioventricular node again specialized heart fibers this is gonna get the signal from the SA node so the SA node is saying let's beat 63 beats per minute we're gonna get that signal to the AV node so this is located in the right atria as well it's just in the lower part so the AV node has two functions the first one we want to delay the signal the SA node is going to send the signal to the AV node so that's gonna take a little bit of time plenty of time for the atria to contract and so then the AV node is going to send the signal down the ventricles because we need a little bit of time for that atria to respond right otherwise all four chambers of the heart are going to be at exactly the same time so it gives us a little delay so the atria have plenty of time to contract and release their blood before the ventricles do this also sends the signal down what's called the bundle of His or the AV bundle so hopefully this picture will help like I said you're not responsible for any of this for lab and there's no diagrams on any of my lecture tests we just kind of need to know how these nodes work so if we look at this picture you have the SA node there on the right side up in the corner on the right atria there looking kind of greenish looks a lot like nerve tissue doesn't it remember it's muscle tissue so the SA node is what we call the pacemaker so he's going to set the pace and if you look at those branches the green how it goes to both atria at the same time and then we also have the branches that are sending the signal to the AV node so this is really important the SA node sends the kind of sets the signal 60 to 80 beats per minute and these junctional fibers these green branches shown here in the atria we have to stimulate both atria at the same time we also have to send the signal to the AV node so we have plenty of time for the atria to fully contract before we send the signal down the red there the AV node down the AV bundle to stimulate the ventricles so if you look once that signal leaves the AV node it starts in the AV bundle and then it Forks so this is a really important thing that this bundle Forks here because think of that muscle tissue you've seen it in lab by now how thick it is and beasty it is in that heart muscle we have to split the signal because the myocardium especially on that left side right is so thick so this would be like me trying to talk to you through a brick wall so we have to fork that signal so that way we're making sure we stimulate both ventricles for contraction so the signal travels down this AV bundle or bundle of hissed a call it goes to the end of the ventricle and then see how it goes back up up the ventricle so it's very important that contraction begins at the apex of the heart which remember is just that pointy structure at the end of the ventricles so I think of it like toothpaste you're supposed to squeeze toothpaste from the bottom of the toothpaste right you're not supposed to squeeze from the top of the tube or from the middle of the tube because you'd be leaving all that toothpaste behind so contraction of the ventricles the same way if bat didn't fork and travel that signal all the way down to the bottom of the heart ventricular squeeze might happen like halfway down and when you squeeze it then you'd be losing all of that blood or leaving all that blood behind that's in the apex of the heart so this is written out here that the AV bundle it's important that it runs down that interventricular septum it has to fork because the myocardium in that interval intraventricular septum is just too thick and beasty so we need to make sure we're carrying the contraction signal from the AV node all the way down to the ventricles so it's gonna branch and then it's going to come up and become the Purkinje fibers once it starts heading up the outer heart wall so the Purkinje fibers are just making sure that contraction is beginning at the apex and pushing the blood up towards those semilunar valves to either squeeze the blood out the aorta to feed the whole body or to squeeze the blood out of the pulmonary trunk to get to the lungs so these fibers are all about carrying the impulses through that thick ventricular wall down to the apex and back up so the pathway of this the signal begins in the sinoatrial node we send it to the AV node allowing time for the atria to contract we then send the signal down the bundle of hiss and back up the Purkinje fibers to make sure that the contraction begins at the tip of the apex of the heart but what if your SI nodes not sending a fast enough signal somebody's got to be the winner chicken dinner so how many times have you watched a race and like won horses favorite or one nascar guy is expected to do the best and then he doesn't maybe blows a tire maybe the horse breaks a leg well then whoever's in second place is going to be your winner chicken dinner so if your essay note is not doing its job the we can get an artificial pacemaker so if the SA node is starts you know kind of not behaving well say you get some kind of an injury or a disease the AV node can take over but the SA node is what signals your atria to contract so if the AV node take over it's we're not getting like the maximum efficiency of our heart if we go back to percentages we've had before if you remember I said 70% of the blood moves on its own so you're getting about 30% of the blood moving from the atria to the ventricles because of atrial contraction so in this case if the SA nodes not working you're not really going to get a strong atrial contraction but you still have 70% of your blood moving just fine so it's almost like saying if your SA node is not doing its job your heart's losing about 30% efficiency with it which if you're a couch potato like me who lays on the couch and watches Netflix you probably wouldn't notice but if you're a young athletic person a 30% lowering of your efficiency is a pretty big deal so the point is we usually surgically deal with it so this picture is showing an artificial pacemaker being put in but it's not something that instantly kills you so this whole class is about homeostasis which is regulation so just like everything else we have to regulate our cardiac cycle we have to regulate our heartbeat so the primary way is that knodel system the SA node picks a pace and tells the whole heart to get on board but of course other factors can affect your heart right exercise isn't that always the answer the answer is never Donuts in tequila it's always exercise but exercise certainly affects your heart right if you exercise your heart rate goes up body temperature o Illinois so as much as I you know I'm kind of getting tired of winter I get tired of winter I hate summer and then when it's summer I'm tired of summer and I want it to be winter basically I'm just never happy but I hate Illinois those hot summer days when you feel your heart beating in your ears because it's just so freakin hot well that happens because of my little note there that when you're really really hot your blood vessels dilate so that's why you get real red in the face right well when your blood vessels dilate they're getting bigger to release all that heat and especially your blood your Bloods about two degrees warmer than the rest of your body so if I'm trying to release that heat I'm gonna bring it really close to the surface so if I'm trying to pump all that blood though and now the blood vessels have got all big my heart's gonna have to work a lot harder to maintain blood pressure concentration of ions remember calcium from A&P one is for contraction and potassium for relaxation so you may have a situation where your heart is affected where it's either kind of too stressed out or it's just kind of lay in there so a lot of guy on go into muscle contraction of course so we're just focusing on the big to calcium and potassium so calcium for contraction easiest way to remember it they both start with C potassium for relaxation and the way that I think of this is people that get a lot of muscle cramps like runners they eat a lot of bananas right to relax their muscles well the heart is affected very differently by these things so it all goes back to homeostasis we want things to be just right so too much of something would be hyper not enough would be hypo so for the heart no exception we got to have the perfect amount of calcium so hypercalcemia having too much calcium is gonna cause your heart to potentially cramp to potentially prolong its contraction and that's not good hypocalcemia is the heart's just gonna pretty much just lay there so neither one of these is good right we need contraction to be nice and strong we don't want it to be too strong we also can't have it be too weak whereas the potassium affects your ability of your heart to relax so hyperkalemia decreases the intensity of your contraction and hypo it may just not even be able to function at all it might just completely stop so we care about both of these and stuff you know anyone with a history of heart issues they monitor both their calcium and their potassium my father-in-law's had several heart attacks and he can't eat things like spinach or broccoli because it has so much calcium in it and he's not allowed to eat bananas because it has so much potassium in it so they really care about regulating his calcium and potassium because we don't want his heart to contract too much because it's weak but we also don't want it to relax too much either because it's already been damaged so one of the major things we have to maintain is blood pressure so your essay and your AV node are controlled both sympathetically and parasympathetic lis so remember sympathetic is fight or flight run real fast or kick some ass and parasympathetic is about rest and relax and digest so we got to have a balance between these two right just like in your life you have a balance I always say I work hard to play hard I got to have that balance so sympathetic is going to increase the intensity of the contraction and parasympathetic is going to put the brakes on so these guys work together constantly to maintain the perfect blood pressure so one of the nerves that does this is the parasympathetic nerve so that's is the parasympathetic nerve is the vagus nerve so this is that cranial nerve number 10 that I mentioned a few slides ago and so you can see it coming from under this skull straight down the neck this innervates a lot of your organs including the heart and I always remember that because I think Vegas Las Vegas affects all of your organs right eat too much at the buffet your stomach hurts you're going to pee a lot because you're drinking alcohol and your heart is definitely affected by Vegas you get really excited or you get really depressed right well this in this case the vagus nerves job is to depress your heart so if a deer runs out in front of you and your Adrenaline's pumping and your heart's racing or if you're exercising too hard and your heart's getting way too elevated the vagus nerve will put the kibosh on this because ultimately even though the heart is self stimulating the brain is in charge so the medulla oblongata is what kind of sets the pace of your heart and then it is the heart's job to send that signal throughout the heart and keep it going every minute of every day but ultimately your brain can say no no no or yay yay yay so the baroreceptor reflex so barometer remember is like pressure in the air so this is a pressure receptor or a stretch receptor so baroreceptors are there to make sure we know that blood pressure is rising or falling so if we think about this this is very common-sense if you're trying to check to see where blood pressure is the strongest you're gonna check the carotid which is going up your neck and the aorta because it's never gonna be any better than that right these are the two major arteries that are coming straight off the heart and so if the blood pressure and the carotid is weak your brain is not gonna get fed if the blood pressure in the aorta is weak your entire body's not gonna get fed so these are two really great places to check blood pressure because if those guys are too high or too low we've got problems so especially if your blood pressure is too high your baroreceptors are gonna tell your medulla oblongata which has what's called the cardio inhibitor Center inhibitions mean to stop right so of course you don't want to stop your heart but this simply means to slow it down so if your blood pressure shoots up it's gonna inform the brain hey blood pressure is really high we want to make sure we don't pop any arteries in our brain so we're gonna tell we're gonna send the signal down that vagus node to tell the heart to slow down which will reduce blood pressure so your arteries and arterials which we'll be getting to very soon or how we of course send the blood away from the heart so a and away so vasodilation and vasoconstriction are two ways we can either speed up or slow down that blood and so I kind of drew it here to try to make it look a little bit kind of make it make more sense so the sympathetic remember fight-or-flight so if you get scared you want to speed that blood up right if I'm being chased by a lion Tiger bear oh my or a guy with a chainsaw I need to make sure I'm getting oxygen to my muscles and sugar and picking up the waste as quickly as possible so think of it like a garden hose if I'm trying to water my plants that are across the garden I put my thumb and kink the hose right so by kinking the size of the hose I'm speeding up that water so we do the same thing here so if you have sympathetic stimulation of your artery walls of the muscle that's in there it's gonna kink your hose so look at this little vasoconstriction picture well that's going to include that's gonna increase your blood pressure if you've ever done this with a garden hose you can feel how that water pressure is going up when you kink the hose it's like so desperate to escape that tiny little straw that pressure goes up consequently if you're relaxed then we're gonna dilate these blood vessels and so that's why the arrow is pointing down decreased stimulation sympathetically means you're relaxed right no more lions tigers bears oh my so my blood vessels go back to normal so they vasodilator this is going to lower my blood pressure because now the fluid is not flying through there so intensely so you're more relaxed your blood pressure goes down you we will have a lab on this or you've already had the lab on this it just depends on where you're at in the lectures but we will eventually have a lab on EKGs or ECGs and this is a representative of the electrical activity of your heart so we're actually going to use this paper that has this little checkerboard pattern and you're going to get a printout of your heart activity so the important thing to remember about an EKG or ECG is this is measuring the electrical activity of your heart this is not measuring contraction even though we can infer it that's not what it's measuring so this measuring is the electrical the electrical change of your heart this is not measuring the contraction strength but we can just assume that but it's not measuring that this is measuring the electrical activity of your heart so this is why they do this in every movie when people flatline and it's all dramatic right it's because we know what a normal EKG looks like we've seen those movies with the little blip blip blip like the little picture above so we know what normal looks like so when you have an irregular pattern we know something's very wrong and we can specifically tell anatomically where the issue is by using these machines we can also get heartbeat from this so part rate we can get beats per minute from an EKG and so we'll be doing that in lab as well but for lecture we just need to know what the p-wave stands for the QRS wave and the T wave stands for so the P wave is atrial depolarization this is when the atria is contracting but that's not what the EKG is measuring so if I ask you what the EKG is measuring with the P wave atrial depolarization which means sodium is rushing into that atria the QRS complex is ventricle depolarization sodium rushing in to the ventricle which is yes ventricular contraction is the result just like when sodium rushed in an A&P one muscles contracted as a result but that's not what it's measuring and then the T wave this is ventricular repolarization which is a relaxing so now the potassium is rushing in no more sodium is coming in so we say repolarization because we're repolarizing we're going back to our resting relaxed state so again the EKG is measuring depolarization and repolarization however I can look at that EKG and I know what's happening as a result so I measure temperature with a thermometer but you know you start sweating so the thermometer is not measuring sweat it's measuring temperature sweat as a result I know I'm gonna sweat when it's 90 degrees I know I'm gonna shiver when it's 20 degrees so we know the atria is contracting and during the p-wave and we know the ventricles contracting during the QRS wave we know the ventricles relaxing during the T wave so if you're paying attention to this you'll notice there's no atrial relaxation an EKG cannot measure the atria relaxing which would be atrial repolarization because it happens during the time the ventricle is contracting and so since the ventricles contracting ventricular depolarization gets in the way so we can't really measure it so it's kind of like if someone is standing next to me talking I'm always gonna talk over them I'm always gonna be louder because I'm a teacher so although that person's talking you wouldn't be able to hear it so the atria is repolarizing but it's happening during the ventricular depolarization can't measure it so we will see this in greater detail in lab so it's the electrical impulses that start the contraction the contraction is a mechanical event after the electrical like I said sweating after the temperature going up the EKG is measuring that electrical impulse not graphing the contractions of the heart but we can just assume that is what is happening so there's a lot going on with the heart right so this picture is just kind of showing the heart sounds the EKG a lot of things going on it's just to basically say a lot going on in the heart you will not have this picture in lecture I don't do pictures on lecture exams but for lecture you'll want to know what's happening in the p-wave what's happening in the QRS and what's happening in the T wave for the lab practical I would give you this diagram and I could ask you that same thing or I could just highlight one of the waves and say which wave is this and then your answer would be P QRS or T but we've addressed that in lab or we will depending on where you're at