Sarcomere Length-Tension Misconceptions
Keywords: muscle contraction, lattice spacing, length–tension curve, spatially explicit The LT curve describes the maximum isometric force a muscle generates as The rise and fall of force with sarcomere length is an indicator that the basic .. A single 1 ms time-step in the model consists of allowing each myosin head to. Subsequently, the sarcomere length-tension relationship was scaled to the fiber consisting of a contractile element in parallel with a passive elastic element. and proximal muscle-tendon junctions to define muscle length and measure it at . It follows a predictable length-tension relationship, and this is fairly could tell me that this relationship consists of an ascending limb at short lengths, term to describe the length at which sarcomeres produce the most force.
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So this is kind of what the actin would look like. And, of course, I want to make sure I draw my titin. Titin is kind of helpful, because it helps demonstrate that there's now a little bit of space there where there wasn't any before. And so now there is some space between the z-disc and this myosin right here. So there is some space between these myosins and the z-discs. In fact, I can draw arrows all the way around. And so there is a little bit of work to be done.
But I still wouldn't say that it's maximal force. Because look, you still have some overlap issues. Remember, these myosins, right here, they're not able to work.
Length-tension relationship :: Sliding filament theory
And neither are these, because of this blockage that's happening here. Because of the fact that, of course, actin has a certain polarity. So they're getting blocked. They can't do their work. And so even though you get some force of contraction, it wouldn't be maximal. So I'll put something like this. This will be our second spot. This will be number two. Now in number three, things are going to get much better.
So you'll see very quickly now you have a much more spread out situation. Where now these are actually-- these actins are really not going to be in the way of each other.Muscle Contraction - PhysiologyZone - Muscular Series
You can see they're not bumping into each other, they're not in the way of each other at all. And so all of the myosins can get to work. So the z-discs are now out here. My overall sarcomere, of course, as I said, was from z-disc to z-disc. So my sarcomere is getting longer. And you can also see that because now there's more titin, right?
And there isn't actually more titin. I shouldn't use that phrase. But the titin is stretched out. So here, more work is going to get done.
The length–tension curve in muscle depends on lattice spacing
And now my force, I would say, is maximal. So I've got lots, and lots of force finally. And so it would be something like this. And so based on my curve, I've also demonstrated another point, which is that, the first issue, getting us from point one to point two, really helped a lot.
I mean, that was the big, big deal. Because you needed some space here. Again, this space really was necessary to do work at all. And now that we've gotten rid of the overlap issue, now that we've gotten these last few myosins working, we have even more gain.
But the gain was really-- the biggest advantage was in that first step. Now as we go on, let's go to step four. So this is step four now. As we go here, you're going to basically see that this is going to continue to work really well. Because you have your actin, like that, and all of your myosins are still involved in making sure that they can squeeze.
So all the myosins are working. And our titin is just a little bit more stretched out than it was before. And our force of contraction is going to be maximal. And you're going to have-- and so here, I'm drawing the z-discs again.
Length tension relationship
They're very spread out. Our sarcomere is getting longer and longer. And our force of contraction is the same. Now let's just take a pause there and say, why is it the same? Why did it not go up? Well, it's because here, in stage three, you had 20 myosin heads working. Up here, you had something like 16 out of 20 working.
Here, we said maybe zero out of 20 right? And here, you again have 20 out of So you still have an advantage in terms of all of the myosins working. But there's no difference between 0. Because again, all the myosins are working. So now in stage five, we kind of take this a little too far, right? So let me actually just make a little bit of space here. We take this a little bit too far in the sense that our actin is going to slip out all the way over here.
And it's going to be out all the way over here. So we've got a huge, huge gap now. And, of course, our titin is completely stretched out. It's about as stretched out as our titin is going to get. This green titin protein. And now the question is, of course, would you get any force? And the answer's probably no. Because the myosins aren't even touching the actins anymore.
So really, again, you have zero out of 20 myosins at work.