Say you've got a muscle. Well in that muscle is made up of a bajillion fascicles. Then those fascicles are made up of a bajillion muscle fibers... Then inside those muscle fibers are myofibrils, which divide into actin and myosin filaments. I understand what this picture looks like. Try and get over your Freudian slip.
So sarcomeres are the basic contractile unit of the muscle Sarcomeres are made up of actin and myosin filaments.
Actin are the "thinner" filaments, and myosin are "thicker."
To recap what I said like four sentences ago, myosin and actin are the main components involved in the contraction of muscles.
Myosin LOVES actin. Like really loves actin.
Actin likes myosin too, but not that much. Actin has myosin-binding sites that, when at rest, are blocked by tropomyosin. Think of tropomyosin as actin and myosin's chaperone.
However, when calcium ions enter the picture, troponin comes in, binds, and moves tropomyosin away from the myosin-binding sites.
Tropomyosin says "Make room for Jesus!"
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