Mighty Muscle

Muscle breakdown
Skeletal muscle (top right) consists of bundles of long, thin cells called muscle fibres. A group of five muscle fibres with surrounding blood vessels is shown at centre. Each muscle fibre contains numerous "myofibrils", one of which is shown at lower centre. The myofibril is a bundle of two types of protein "myofilament": myosin (green) and actin (red). When the muscle is stimulated, tiny cross-bridges (lower left) in the myosin filaments hook onto actin filaments and pull them along. As a result, myosin and actin filaments slide over each other, shortening the muscle and making it contract.

Actin and Myosin
The thin filament (top) is composed of actin (yellow), tropomyosin (white strip) and troponin (white oval). The thick filament (pink) is composed of several chains of twisted myosin with globular protruding heads. The interaction between myosin and actin is critical to muscle contraction.

Contraction

Simple animation of sliding theory

Muscle contraction I showed in class

How does it all work?
the colouring handout that I gave you explains this really really well.

The Tropomyosin (which is composed of 2 strands) has Troponin attached to it, and winds around the Actin.

The Tropomyosin covers the sites where myosin is able to bind, so myosin is not able to bind. In this state, the muscle is in the relaxed position.

When you want to contract a muscle, Your brain sends a nerve impulse signal to your muscles. Chanels open and release Calcium ions into the blood at the site of the muscle. Calcium binds to the Troponin, which goes through a confirmational change --> it changes shape, causing the structure to change shape, making the tropomyosin move off of the binding site.

The myosin head is then able to bind to the binding site.
this process requires energy (for the myosin head to slide along the actin) so ATP is used.

does that make sense?
take a look at the animation, as well as oxford...it has good detail.

If you have any questions, please come and see me before class...I should be in the office around 8am...if you want me in earlier, just let me know. I also have first period off. (well, not off..it's my prep period)

Hope that helps, and Im sorry for not posting this sooner.