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Current time:0:00Total duration:13:45

Video transcript

something that I really really enjoy doing and I and I have done it a lot is camping and so I'm going to start by telling you a little story of a recent camping trip and I like to in the morning let's say around 9:00 a.m. head down to the river it's always kind of a fun thing to do and so this day was no different I went down to the river feeling good and had a big smile on my face and what I want to do is kind of think about that moment in fact if we stop time around 9:00 a.m. as I was down by the river what would you see in my heart what would you have actually noticed now the heart has of course nerves leading up to it so we've got sympathetic nerves and the sympathetic nerves at all times are kind of releasing some amount of their neurotransmitter and the neurotransmitters of course just some chemical that helps communicate a message so this is my neurotransmitter and I'm going to name it norepinephrine which is the one that this particular one will be releasing and so the norepinephrine is headed from the nerve and it's headed over to my heart cell and so of course my heart cell it has little receptors on the surface and let's say that of these three receptors one of them gets the signal and this guy right here releases now this signal in the in this heart cell and of course calcium is going to come into the heart cell and we've talked previously about exactly how that happens but you know that that happens and if that calcium gets into the heart cell which which here it does where is it going to go well you have of course muscle proteins myosin actin in that heart cell and those muscle proteins are going to basically require a little bit of calcium in order to work properly so this is my myosin and let me now draw some actin this is actin protein and this actin I'm showing in kind of a crunched situation right this actin is kind of crunched together and when I say crunched I basically mean that there's a little room because this is going to be the end of systole let's just assume that we're at the end of systole here and I'll write that here and systole so it turns out that I guess when I froze time at 9:00 a.m. when I froze time it happened that I caught this magical little time point end systole and some of that calcium is of course binding to troponin C and I'm just going to kind of scatter some calcium randomly so I really am not putting too much thought into exactly where it goes but it's kind of throwing it out there and now our question is going to be how many myosin heads are actually working and I'm going to circle the ones that are working in red so this one is working because it's close to actin and there's calcium on there and it's the right polarity but the next one over this one I'm not going to circle because it's the wrong polarity this one has calcium that's too far it's on the wrong side and this guy well this guy actually would be circled because he's got calcium on the right polarity actin this guy I would circle as well for the same reason and these two I cannot circle because they're the wrong polarity but this one I will circle so we've got about 4 out of 20 that are working and I could actually just rewrite that as some 4 out of 20 works out to what 20% so 20% of my myosin heads are working so that's you know that's not great but it's it's not awful either so to kind of sum this up at 9:00 a.m. I was walking along the river and at that time at the end of systole if you actually wanted to see how much of my myosin was actually working you'd say 20% now that night 9 p.m. an interesting thing happened I also headed out went outside and wanted to kind of do one last little look around and I encountered a scary animal a scary beast I would even say and this animal had four legs and let's see if you can recognize it had a striped tile tail and a striped body and this horrible horrible little creature is none other than a raccoon so this is my little raccoon with a ugly little face and this raccoon like many raccoons do scared me and and you should know I I do actually in fact have a fear of raccoons and so this was a very scary event for me I I shrieked and I was not too happy so what was going on in my heart at that time let's actually do a little cut paste job alright so now I'm basically just going to try to cut and paste some of this and I'll erase the parts that are not relevant right so I've got something like that and let me just quickly erase the parts that I know I'm not going to want so let's start there I've got my sympathetic nerves that are now going to be going crazy I'm going to dress draw a giant arrow because they are going to be driving a message down they're saying hey this raccoon is awful and scary let's just get lots and lots of neurotransmitter release so they're going to just release tons and tons of neurotransmitter and that is an important issue right this is how signals get passed and so of course now all of my receptors are jamming that signal and of course that signal means that calcium is going to flood my cell all of a sudden I have much more calcium in my cell that I used to tons and tons of calcium in fact we know that this is the key way that our nerves are able to communicate a message they basically help by sending ions into cells so now our cell is jam-packed full of calcium and so now I can just kind of scatter calcium everywhere I just kind of sprinkle it all over the place and let's see what happens now so I've got calcium everywhere and same question as before you know where does or how many cells or how many myosin heads rather are going to be working for us so let's just circle the ones that are working for us we still have a few that are not going to be working because they're blocked by the wrong the polarity actin but these are actually now all recruited all of these are and on the other side I've got some recruitment over here so I've got lots and lots of myosin heads recruited I've got let's see if I can count it up five ten eleven twelve so I've got 12 out of 20 or that works out to 60% so 60% up from 20% I'm going to make a little bit of space on a canvas now but just kind of think about that the fact that 9 a.m. in the morning my heart at the end of systole was cranking out at 20% and now it's working at 60% so what does that mean exactly well you know how can we kind of put that together in an image that we can kind of remember and think about and make sense of so for this part I think it'd be helpful to kind of go back to our pressure-volume curves so we've got this idea that at the end of systole we have a relationship called the end systolic pressure volume relationship right I'm actually going to draw it out here something like that this is all this is a sketch of our end-systolic pressure-volume relationship and we know and yellow will be kind of our 9:00 a.m. let's just kind of keep that in mind this is what was happening in the morning as I was relaxed and at the end of systole I said we had about 20% of our myosin heads working so if I was let's just take a spot here and I could take any spot I'm just kind of choosing it randomly and let's say this is the volume at that spot and if I fill it in with blood it would look like that and at this point we've got our workers remember our workers kind of represent how much force of contraction there is so workers are kind of yanking this way in that on this rope and our worker up I'm just going to kind of quickly sketch out maybe looks like that and we've got another worker down here long arms apparently and if I was to look at my workers faces because I've drawn the faces very very small it's hard to see them you know they're yanking right this night there they're not lazy they're not just standing there but they're yanking and this is the face of someone that's working let's say 20% now at that same moment let's say instead of yanking it 20% let's say I yanked at I don't know 60% you know just to make it kind of the same as the other one if I was yanking at 60% well now I would actually create more pressure right so same volume and I'm actually going to just kind of sketch higher up maybe something like this so at that same volume it would basically look like this and I'm going to try to draw the exact same volume so you believe me this is let's say the same volume about the same anyway and here let's fill it up with blood we've got our two workers doing kind of the same thing we've got workers yanking on this left ventricle and these workers are working much harder right so they're working much more diligently than previously and they're yanking of course same directions opposite from each other and these workers if you were to stare at their face you'd notice they're really into it they're really really trying to Gurr they're really really trying to pull apart on that left ventricle as they're working so much harder and actually maybe I should even write the percentage in here let's write 60% here they're working so much harder what that does is for any given volume the same volume they're going to have a much higher pressure so these are going to be able to drive a higher pressure and that's what you see right mean there's basically this volume is the same I've tried to sketch it to be the same but that you can see it's the same exact point and yet the pressure is much higher now going back to and this is of course our 9:00 p.m. this is when I was scared this is my 9:00 p.m. sketch now going back to the 9 a.m. the morning sketch let's say I was to pull a little bit of volume off of my heart well the pressure would fall and it would keep falling and so remember this is how we even created this line in the first place and it kind of ends down here and at 9:00 p.m. in the evening I could do the exact same thing I could say well you know if I drop the volume a little bit I'll get a lower pressure and if I drop the volume again I'll get a lower pressure and it eventually also heads down to the same spot because remember you do need a minimum amount of volume some minimum amount to be able to even generate pressure and that's going to be the same minimum amount for both of the situations right so you need that same minimum amount but as you go higher from that point you actually go along a different slope and so really what you're creating is two lines of a different slope and the difference is really reflected in our percent work so our 60 percent line is different from our 20 percent line and I could even you know kind of test you I could say well what if what if I was to draw a line I'm going to just make a little bit of space now what if I was to draw a line somewhere in the middle what if I drew a green line that looked like this what would be the it would be a gas as to what percent work that is and you say well you know it looks like something between 20 and 60 I don't know maybe 40 percent so this would be your guess just by looking at the line so what you're saying or what I'm saying really is that you can change the line the slope of the line up or down and what that reflects is how hard your muscle is contracting and that goes back to the myosin heads that you're using to contract and so what this really means the slope of the line and these three lines that I've drawn here really reflect an idea called contractility contractility and you'll see contractility mention all the time and all it really means is kind of the slope of that line and you can change the slope of the line the main way is through calcium so calcium more or less calcium changes the slope of the line remember that's how our sympathetic nerves work so this is kind of the main way that our sympathetics change or affect not line sympathetic nerves and finally I want to make sure that you don't get the idea that that's the only way to change contractility you can also kind of change the pH or you can change the temperature all these things will sect how well myosin can work because of course myosin is a protein and proteins need an ideal pH or temperature but you know I mentioned that just so you know that but truthfully the one that we always seem to talk about or always kind of think about is this one and the main reason is because that's something that our sympathetics have gotten so good at controlling