Our example tells us that two tension graphs are shown below, one for cardiac contractile tissue and one for skeletal muscle tissue. In both graphs, the yellow line represents tension in the cell, and the red arrows represent the arrival of an action potential. Alright. So it says here, a. Identify which graph shows cardiac contractile tissue and which shows skeletal tissue. Well, first off, we'll look at the graphs here. We have the y-axis for both of them as tension, and the x-axis is time. And we see here on the left-hand graph those arrows representing action potentials. We see a lot of them coming in rapidly, and we see that this tension line sort of goes up and down, up and down, up and down, but it keeps on climbing until it just stays with a lot of tension. The graph on the right, we see action potentials. There are two of them. They're nicely spread out, and in between them, we get tension and relaxation. And then again, we get tension and relaxation. Alright. I've been through all that. Hopefully, this is pretty straightforward which one represents skeletal muscle and which one represents cardiac muscle. Well, the one on the left, I'm going to say, is skeletal. Remember, skeletal muscle can have really rapid action potentials, and as they come in rapidly, they come in faster than that muscle has time to contract and relax. So it contracts a little bit. And then before it can relax, another one comes in, and it contracts more. Another one comes in. It contracts more and more and more until you get up to what we call here this titanic contraction, where it stays contracted and just stays squeezing and holds like that. Now, in contrast, cardiac muscle, well, that's this one over here. So right here, cardiac. These cardiac contractile cells, the action potentials are going to come in nice and spread out. That allows these cells to squeeze, to contract, and fully relax again before they are stimulated again. Now, that's important for a heartbeat. Right? Because you want your heart to squeeze and relax and not just squeeze and hold because that wouldn't pump blood. Alright. So it says here for b, the skeletal muscle shown is exhibiting a titanic contraction. How does the molecular physiology of contractile tissue prevent tetanic contractions in heart muscle? Alright. So again, remember, tetanic contraction, those contractions that squeeze and hold, we said that's important for skeletal muscle because if you're holding something heavy or holding your baby, you don't want those muscles just to release. You want it to just stay contracting. But in the heart, that's bad because we need to pump blood, pump, and release. Well, we said that the way that cardiac muscle stops from having these tetanic contractions, we said that they have a prolonged or I'm going to say prolonged absolute refractory period. And that absolute refractory period is the time between action potentials when a cell cannot depolarize because it's already depolarized. An action potential cannot stimulate a depolarized cell. Remember, in those contractile cells, you have that long plateau phase, which stretches out the time that it's depolarized. So even if a new action potential came in, it couldn't tell the cell to contract. This gives those cells time to contract and relax before they can be stimulated by another action potential. Alright. For that, we've matched up our muscles. We've explained why they work that way. More practice to follow. Give them a try.
Table of contents
- 1. Introduction to Anatomy & Physiology5h 40m
- What is Anatomy & Physiology?20m
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- Simple Epithelial Tissues1h 2m
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- 5. Integumentary System2h 20m
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- 25. The Urinary System2h 39m
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18. The Heart
Cardiac Action Potentials
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