Sarcomere Components

I remember when I used to get all the different parts of the sarcomere mixed up, but with a few simple tricks you can remember it easy and long-term.

First, understand the the I band is isotropic and the A band is anisotropic. Although these terms technically refer to the behavior of polarized light passing through, I like to think of isotropic = moving and anisotropic = non-moving (remember that “an-“ means “without”).

So how do you remember which is the thick filament and which is the thin filament? Just remember that the heavier something is, the less likely it’ll move! In other words, think of the thick filaments as too heavy to move which means they’re the A bands because “an-“ (or “a” if that’s easier for you) means “without”. By default, the thin filament will be the I band. Additionally, the letter “I” is thinner than the letter “A” so it’s gotta be the “thin” filament right?

Now Z lines are you endpoints which should be easy to remember, because the letter “Z” is at the end of the alphabet. This actually ties into the next point too.

The points that “move” during muscle contraction are the H band and I band which spell “HI”. In other words, the “HI” bands bring the ends of the sarcomere (Z lines) closer together so they can say “Hi”!

Obviously this doesn’t cover everything you should know about the sarcomere and muscle contraction, but hopefully it helps get you started if you were having trouble!




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