What structural unit within skeletal muscle is responsible for the characteristic cross-striations?

What structural unit within skeletal muscle is responsible for the characteristic cross-striations?

• A. Sarcomere.
• B. Myofibril.
• C. Mitochondrion.
• D. Nucleus.

Answer: (A)

The sarcomere is the basic repeating contractile unit that creates the cross-striation pattern in skeletal muscle. Each myofibril is made of many sarcomeres lined end to end from one Z-disc to the next. Within a sarcomere, thick myosin filaments and overlapping thin actin filaments produce alternating dark bands (A) where overlap is greatest and light bands (I) where only thin filaments are present. This organized arrangement gives the characteristic light-dark pattern seen under light microscopy. The boundaries between sarcomeres are marked by Z-discs, and the center of the sarcomere contains the M-line. Myofibrils display the striations because they are composed of many sarcomeres, while mitochondria and nuclei do not define this repeating pattern.

The sarcomere is the basic repeating contractile unit that creates the cross-striation pattern in skeletal muscle. Each myofibril is made of many sarcomeres lined end to end from one Z-disc to the next. Within a sarcomere, thick myosin filaments and overlapping thin actin filaments produce alternating dark bands (A) where overlap is greatest and light bands (I) where only thin filaments are present. This organized arrangement gives the characteristic light-dark pattern seen under light microscopy. The boundaries between sarcomeres are marked by Z-discs, and the center of the sarcomere contains the M-line. Myofibrils display the striations because they are composed of many sarcomeres, while mitochondria and nuclei do not define this repeating pattern.