Question

Lab 2: The Muscular System

Q1. In the context of skeletal muscle histology, what are "striations"?
Q2. Understanding muscle striations is a matter of understanding what the alternating dark and light stripes (pictured above). First, the dark stripes. Do the dark stripes correspond to the entire length of the thick filaments, the entire length of the thin filaments, the region with both thick and thin filaments, or the region where thick filaments are absent?
Q3. Now, the light stripes. Do the light stripes correspond to the entire length of the thick filaments, the entire length of the thin filaments, or the region with both thick and thin filaments, or the region where thick filaments are absent? Q4. The figure shown above shows a portion of a muscle in a relaxed, elongated state. If this muscle contracts, which sections will get narrower – the dark stripes, light stripes, both, or neither? Briefly explain your reasoning.
Q5. In some versions of this lab, students added ATP to fresh muscle fibers, which was supposed to cause them to shorten. However, it did not usually work; the fibers generally stayed the same length. Provide one possible reason for this lack of shortening.

Answer 1

1) Straition in skeletal muscle means muscle tissue having transverse dark and light bands made up of elongated fibers.

2) Striated muscle is composed of myofibrils that show alternating light and dark bands that give the appearance of striations of the muscle. Light bands are formed by thin filament or actin alone. Dark bands are result of overlap of thick and thin filaments.

3) Light band - corrosponds to the region of thin filament.

4) On contraction - Light band narrows.

As the muscle contracts there is overlapping of thin and thick filament. Due to which z lines comes closer. Dark band remains same, but the light bands narrows.