Archive for August, 2008

How stuff works… in a nutshell!: Sarcomeres

Posted in science with tags , , , on August 3, 2008 by freakychinaman

Sarcomeres are the basic functional units of muscle (be it skeletal (ones you show off) or cardiac (heart), but  NOT smooth muscle!… however the principles below still apply), and they stick end on end to form myofibrils (if you ever see “myo” it means “muscle”), which gather to form the muscle fibers and blah blah blah.. gather to form your everyday muscles . And if you want to know how they contract you really only need to worry about 2 things: actin (thin) and myosin (thick) filaments.

I like to think of the myosin filaments as caterpillars…. that have 2 heads: so as you can see from the picture above, the myosin filaments have little ‘legs‘  sticking out at the 2 ends (but they like to call them heads….) and what those 2 pictures at the bottom are trying to say (and doing a crappy job at it..) is that these heads reach out to an actin filament and then attaches itself, then physically pulls the actin towards the middle over and over again (much like how animals walk), which makes the muscle shorten.

If you keep in mind the same image, then you can begin to understand the logic behind the length-force relationship of muscles:

all this says is that when the muscle is stretched or shortened to a point it will start to reduce its ability to produce force (so why it’s harder to do a squat or a push-up if you go lower, despite the fact you are moving the same weight). So back to the caterpillar metaphor: if the branch (actin) is too far but close enough for a leg or 2 to reach, it still really can’t pull itself up the other side and if anything it’ll have to keep scuttling just to stay attached (that vibration you get when you strain?…). And when your muscles are too short, the actin filaments will end up sliding past each other, which means that the ‘legs’ at each ends will actually be working against the contraction as they run along the actin going the opposite way, also when the actin overlaps it stops the myosin from connecting with the filaments it was suppose to; and also the myosin filaments will end up butting up against the ends of the sarcomere.

Anyways that’s my first in-a-nutshell post and I hope it was useful and didn’t confuse/bore you to death. I try to steer away from the molecular stuff for now since it can be extremely boring and extremely long and I want to try to keep these as simple and short as possible (hopefully I did alright this round), and I guess I’ll keep these post to things people can relate to (rather than your school stuff where you spend 2 months learning about how you make pee…. but if you really want to know….).

[Doing this is also beneficial to my study :P]


Hugh Hefner finally grew up:

stage of playlord

[another fashion store in HK somewhere…]