MICROANATOMY

Detailed explanation-1: -Sliding-filament model of muscle contraction. The actin filaments slide past the myosin filaments toward the middle of the sarcomere . The result is shortening of the sarcomere without any change in filament length.

Detailed explanation-2: -Energy from ATP is required for the myosin head to release from the actin filament-otherwise the myosin heads would remain in the same place, and the muscle would not contract. Even though the filaments are moving, the filaments themselves never actually get shorter or longer.

Detailed explanation-3: -As the actin filaments come closer to the M-line, the Z lines come closer together, so the sarcomere also decreases in length. The A band is the only part of the sarcomere that does not change length during muscle contraction.

Detailed explanation-4: -Sarcomeres are highly stereotyped and are repeated throughout muscle cells, and the proteins within them can change in length, which causes the overall length of a muscle to change. An individual sarcomere contains many parallel actin (thin) and myosin (thick) filaments.