hey everyone my name is Heather and today I'm going to talk to you about the sliding filament theory when you look at our skeletal muscle fibers under a microscope you will notice they are striated in nature meaning that they look like they have bands across them well if you look at muscle fibers even closer skeletal muscle fibers are actually formed by two different filaments that give it this appearance the first filament is known as actin and it is very thin also known as the thin filament the second filament is Madison and it is much thicker than actin because it contains a bunch of myosin heads so this is also known as the thick filament muscle contraction is initiated by the brain via an action potential this action potential causes an influx of calcium ions that bind to troponin a protein on the actin filament this causes a conformational change in actin and exposes the myosin binding sites I find it easiest to begin with detachment this is when the myosin head detaches from actin in order for detachment to occur an ATP molecule must bind to the myosin head and when this happens myosin detaches from actin and goes into a resting state the next step is known as hydrolysis in hydrolysis the ATP molecule is split into an ADP molecule and a phosphate molecule this causes the myosin head to change into a ready position and bind to actin since the actin filament has undergone a conformational change and the myosin heads are in the correct position a crossbridge can occur between the two filaments the myosin heads bind to the actin filament next the bound adp and phosphate detach which causes myosin to forcefully change back to its relaxed shape this is known as a power stroke this brings us back to where we began detachment so to refresh and bring things into a full circle another ATP molecule binds to myosin causing it to detach and return to its resting state the cycle continues until the brain ceases movement preventing an action potential therefore action returns to its normal shape and no binding can occur let's sum this up beginning with detachment ATP binds to the myosin head causing it to detach next during hydrolysis the ATP splits into adp and a phosphate which allows the myosin heads to be ready to bind a crossbridge occurs because both the actin and myosin filaments are in the right positions to do so and finally the ADP and phosphate are then lost causing myosin to perform a power stroke thank you so much for watching this video if you liked it please be sure to give it a thumbs up and don't forget to subscribe to my youtube channel be sure to leave me a comment below if you want more educational videos as always happy studying you [Music]