a. Describe the structure of a sarcomere and indicate the relationship of the sarcomere to myofilaments. b. Explain the sliding filament model of contraction using appropriately labeled diagrams of a relaxed and a contracted sarcomere.

Video transcript

Hi, everyone. Let's look at our next question. According to the sliding filaments theory, the ss eye band isotropic bands shortens during muscle contraction, the I band is the area of the scare where the Z discs are anchored as the sarcomere shortens during muscle contraction, the eye band becomes narrower. What happens to the Z diss during this process? Choice A, they move farther away from each other. B, they are degraded C, they move closer together or D they produce A T P to fuel the muscle contraction. Well, to think about what's going on here, it can be helpful to have a diagram and I've put a very rough one here. The Z lines or the line where the Z disks are, mark the edges of the sarcomere. So I've drawn the Z lines in red. So they define the score and the Z line is right in the middle of the eye band. The eye bands I've indicated in black, the eye bands are those regions where there are only thin filaments, draw the thin filaments with thin blue lines. And then in between each eye band, you have the thick filaments which I've drawn with a thick blue line and those thick and thin filaments overlap at the end of the thick filaments, the area of the thick filaments is the A band. So when we think about this diagram, we know that when the muscle contracts, but during a muscle contraction, the thick filaments do not change in length, they remain constant in length. So we can look at our diagram and know that those thick filaments and the A band will remain exactly the same length, but the thin filaments shorten during a contraction. So if we can imagine the eye band is this region where there are only thin filaments. If those thin filaments are shortening, that means the eye band narrows as our question tells us. So now if we think of this whole thing altogether, we have our thick filaments remaining exactly the same, but the thin filaments uh contracting and thus our eye bands becoming narrow, we know the ZIS just run down the center of the eye band. So if the thin filaments are shortening and the eye bands are narrowing, that means that the Z discs are choice c moving closer together due to that narrowing of the eye band. So that is the correct answer here as to what's happening to the Z diss during muscle contraction, they are moving closer together due to the shortening of those thin filaments. See you in the next question.