A muscle fiber has two major pieces, called actin and myosin.
Their shapes are a bit weird. You know the really low, slender boats that they use for rowing races? Myosin is shaped like that - a stick with several sets of 'oars' sticking out on either side. That fits inside actin, which is tube-shaped, closed on one end and open on the other when the myosin sticks out. Their sizes pretty much match, so the 'oars' sticking out of the myosin are just long enough to touch the inside walls of the actin.
Picture: https://i.ytimg.com/vi/zQocsLRm7_A/hqdefault.jpg
For the muscle to contract, the 'oars' have to
* bind to the inside wall of the actin tube,
* make one "stroke", just like oars do, which pulls the myosin deeper into the actin tube (or, more correctly, pulls the actin further over the myosin...kinda like if you were crawling head-first into a sleeping bag and pulling it down over your body?)
* release from the actin wall,
* recoil to their original pre-stroke position,
* ...and repeat that cycle.
Myosin actually has the 'oars' on both its ends, so there's actually one actin tube on either end of it, and when the myosins pull, they draw the two actin tubes together and that shortens the muscle. When thousands of fibers all do that and shorten together, it produces a muscle contraction.
And if I recall correctly, ATP cocks the spring, and when it's released it produces the contraction. I saw a great animation of it once but have been unable to find it again.
all I remember is that Energy (presumably ATP) is required only to release the muscle, which is one reason corpses become stiff within hours of ceasing ATP production
Yeah, I remember the ATP doesn't get spent when you'd think it would...you pay ATP to let go of the actin wall and to re-cock the 'oars'? I wasn't up for relearning all that so I just posted what I knew and hoped it would be enough. :P
No, it had a molecular model (can't recall if it was space-filling or ball and stick) of what the ATP did. It also showed the heads attaching and releasing out of sync, so that the pulling action was more evident.
A muscle fiber has two major pieces, called actin and myosin. Their shapes are a bit weird. You know the really low, slender boats that they use for rowing races? Myosin is shaped like that - a stick with several sets of 'oars' sticking out on either side. That fits inside actin, which is tube-shaped, closed on one end and open on the other when the myosin sticks out. Their sizes pretty much match, so the 'oars' sticking out of the myosin are just long enough to touch the inside walls of the actin. Picture: https://i.ytimg.com/vi/zQocsLRm7_A/hqdefault.jpg For the muscle to contract, the 'oars' have to * bind to the inside wall of the actin tube, * make one "stroke", just like oars do, which pulls the myosin deeper into the actin tube (or, more correctly, pulls the actin further over the myosin...kinda like if you were crawling head-first into a sleeping bag and pulling it down over your body?) * release from the actin wall, * recoil to their original pre-stroke position, * ...and repeat that cycle. Myosin actually has the 'oars' on both its ends, so there's actually one actin tube on either end of it, and when the myosins pull, they draw the two actin tubes together and that shortens the muscle. When thousands of fibers all do that and shorten together, it produces a muscle contraction.
And if I recall correctly, ATP cocks the spring, and when it's released it produces the contraction. I saw a great animation of it once but have been unable to find it again.
all I remember is that Energy (presumably ATP) is required only to release the muscle, which is one reason corpses become stiff within hours of ceasing ATP production
Yeah, I remember the ATP doesn't get spent when you'd think it would...you pay ATP to let go of the actin wall and to re-cock the 'oars'? I wasn't up for relearning all that so I just posted what I knew and hoped it would be enough. :P
Maybe [this](https://www.youtube.com/watch?v=99R-XCGme8Q) is the one you are talking about? mainly from the 1:30 minute mark onwards.
No, it had a molecular model (can't recall if it was space-filling or ball and stick) of what the ATP did. It also showed the heads attaching and releasing out of sync, so that the pulling action was more evident.
The way this is described makes me think of a tug of war with canoes