An earthworm's body consists of a number of fluid-filled compartments, each with its own set of longitudinal and circular muscles. But in the roundworm, a single fluid-filled cavity occupies the body, and there are only longitudinal muscles that run its entire length. Predict how the movement of a roundworm would differ from the movement of an earthworm.

Using examples, explain this statement: 'Vertebrate skeletons are variations on a theme.'

Distance runner Paula Radcliffe has won dozens of long-distance races and held the women's world record for the marathon since 2003. Scientists, trainers, and athletes alike have wondered about the extent to which muscle structure and function contribute to success in athletes such as Radcliffe. What makes elite distance runners so good? Are their muscles somehow different from those of less successful athletes and non-athletes?The researchers looked more closely at the data within the group of elite runners. Although the mean proportion of slow fibers was 79 percent in this group, individual values ranged from 27percent in one runner to 98 percent in another. How does this finding affect your interpretation of the relationship between athletic performance and muscle-fiber types?

Drugs are often used to relax muscles during surgery. Which of the following chemicals do you think would make a better muscle relaxant, and why? Chemical A: Blocks acetylcholine receptors on muscle cells. Chemical B: Floods the cytoplasm of muscle cells with calcium ions.

Distance runner Paula Radcliffe has won dozens of long-distance races and held the women's world record for the marathon since 2003. Scientists, trainers, and athletes alike have wondered about the extent to which muscle structure and function contribute to success in athletes such as Radcliffe. What makes elite distance runners so good? Are their muscles somehow different from those of less successful athletes and non-athletes?Imagine that Paula Radcliffe is racing against a bird and a fish, each with the same mass as Paula. Which organism would have the highest cost of locomotion during the race?

When a person dies, muscles become rigid and fixed in position—a condition known as rigor. Rigor mortis occurs because muscle cells are no longer supplied with ATP (when breathing stops, ATP synthesis ceases). Calcium also flows freely into dying cells. The rigor eventually disappears because the biological molecules break down. Explain, in terms of the mechanism of contraction described in Modules 30.9 and 30.10, why the presence of calcium and the lack of ATP would cause muscles to become rigid, rather than limp, soon after death.

SCIENTIFIC THINKING Imagine you have a friend who had her child's ACTN3 genotype tested. After reviewing the study described in Module 30.12, what cautions would you offer about interpreting the test results?

What type of muscle is striated with intercalated disks?

Which statement about muscle contraction is correct?