Now, the muscle cell it self (gettin' microscopic here), is composed of different connected subunits called myofibrils. Myofibrils composed of two myofilaments made up of Actin, and Myosin proteins. when those combine they look like this(again, bare with me here): =-=-=-=-=-. The dash(-) represents the Myosin. The equals sign(=) represents the Actin. The Actin protein is very thin and surounds the Myosin protein as is some what connects it self around that Myosin protein. Now in the process of our daily muscle movements, the interconnected myofilaments slide in and out of each other as we move our muscles. So, in my make shift example of dashes and equal signs, the dashes (myosin) slide in between the top and bottom lines of the equal signs (actin). Ok, I'm sorry but just one more division of the muscles is needed for even more understanding of the sliding myofilament. A sarcomere, being two actin proteins surrounding one of the myosin proteins (=-= sarcomere), is a sort of subunit that connects to other sarcomeres to make up the basics of our muscles.
The action of the sarcomeres contracting and then relaxing is the actin proteins coming closer to each other and then moving away from each other as the muscles are relaxing and contracting through out our daily processes. As the actin proteins contract and relax, they slide up against the myosin protein that lies in the middle of them. Its very much so like a chain. The links don't ever separate unless extreme conditions lead to one of the links breaking, and when the chain does not have allot of tension on it, it allows the links to move fairly freely within them selves.
The green marker cap would be the Myosin protein. My nasty fingers, would be the Actin proteins.
Better than dashes and equal signs I guess :)
