Question

contractions occur when thin what?filaments slide past thicker what filament, causing the sacomere unit to shorten

Answer 1

Answer-

Sarcomere is the structural and functional unit of myofibril. A single myofibril may be composed of hundred or thousands of sarcomeres that are joined end to end. Sarcomere is defined as portion of the myofibril between two successive Z lines.

The thin filament are anchored to both sides of each Z line by alpha actinin. It composed of contractile proteins actin, tropomyosin, and troponin in a ratio 7:1:1 .

Whereas thick filament located in the middle of each sarcomeres and produces each A band.

I band lies between the ends of A band of two adjacent sarcomeres and include those portion of thin filaments that do not overlap the thick filament.

During muscle contraction the length of the sarcomere decreases. The result in shortening of I band but the length of A band remains unchanged.

So, sarcomere length is decided by the length of of I band.

During cross bridges, the globular head of myosin II Projects from the surface of the thick filaments towards the thin filaments and bridge the gap between them.

During contraction myosin attached to the thin filaments and pull them.