21. The muscles then contract through the sliding filament mechanism, causing shortening of sarcomeres and muscle contraction. 22. Release of sarcomeres of the muscles to shorten, thus leading to the contraction of the muscle. 23. Myofibrils are complex strands of several kinds of protein filaments organized together into repeating units called sarcomeres . 24. Muscle tone or firmness is derived from the increase in actin and myosin cross filaments in the sarcomere . 25. The alpha actins are found in muscle tissues and are a major constituent of the sarcomere contractile apparatus. 26. The striated appearance of both skeletal and cardiac muscle results from the regular pattern of sarcomeres within their cells. 27. These rods are non-pathognomonic structures that have a similar composition to the Z disks found in the sarcomere . 28. Each muscle fiber contains myofibrils, which are very long chains of sarcomeres , the contractile units of the cell. 29. It limits the range of motion of the sarcomere in tension, thus contributing to the passive stiffness of muscle. 30. This is because the sarcomere length, which is the fundamental unit of muscle structure, is similar in length.
