Muscle Bound

An Internet guide to how muscles work


Plastinated giraffe at BODY WORLDS, reviewed by the London Evening Standard


My children tease me about my “fear” of giraffes. It all started after I visited the popular exhibition Body Worlds, the creation of German anatomist Gunther von Hagens. Even after viewing half a dozen “plastinated” and posed human cadavers, each one skinned and dissected to reveal all, I was taken aback by a sixteen-foot-tall giraffe stripped of its familiar hide. With mouth open, I studied the enormous bands of flesh and tendon, once capable of propelling the ungainly creature across a savanna at thirty-five miles per hour. In addition to permanently altering the way I see giraffes, the exhibit revealed muscles in a whole new light.

If examining skinned cadavers is not your cup of tea, the Internet offers less macabre ways to explore the muscles of the human body. A site created by Dr. James Crimando, a biologist at GateWay Community College in Phoenix, uses plastic models and illustrations to help you learn the superficial muscles—the outermost ones that I once memorized for a drawing class. Double click on a muscle to see its name. At the BBC’s Interactive Body, ten muscles are presented, and you have to drag them to the right position in the body. Once you have placed the muscle in the correct location, an animation pops up with controls to show how the muscle moves. Aside from the more familiar skeletal muscles, you can see a bladder in action as it empties or a tongue wagging. Who knew that there is a muscle called the pupillary sphincter in your eye that contracts when the sun comes out from behind a cloud? Each time you play you’ll get a new set of ten muscles to learn.

At Get Body Smart, you can find most of the skeletal muscles presented in a tutorial that allows you to see how they are attached to the bones and to see how each one functions via flash animations. Click on “Home” to find tutorials on other body systems, such the cardiac cycle with the heart muscle beating away. Another good site is the Muscle Atlas created by Dr. Michael Richardson in the Department of Radiology at the University of Washington. Click on “upper” or “lower extremity” to begin.

A place to get some very basic information (via audio, simple animations, and quizzes) is the patient information site maintained by MedlinePlus, a service of the National Institute of Health called Here you can also find some information on muscle diseases and injuries.

To see how muscles do their work, you need to view them at a cellular level. On YouTube, I found an animation by Pearson Education of a muscle cell in action. Having studied geology, I missed out on learning much cellular biology, so when I watched this video, I was really amazed to see the molecular mechanisms that power our every movement. To think of all the muscle cells contracting as I type this!

InsertMedia Error Muscle tissue comes in three types: skeletal, smooth, and cardiac. This YouTube video gives a brief description of the different cells. Here I learned that skeletal muscle cells can be up to a foot long. John W. Kimball, a retired biology teacher, has a Web page with a more academic review of the biology of the different cell types and muscle diseases. In addition to the three types of cells, skeletal muscle is made up of two different kinds of fibers. Go to his section “Type I vs. Type II Fibers,” to learn more about these “slow twitch” and “fast twitch” fibers. Interestingly, the percentage of muscle types varies considerably between individuals. At, sports medicine writer Elizabeth Quinn has a page entitled Fast and Slow Twitch Muscle Fibers: Does Muscle Type Determine Sports Ability? “Our muscle fiber type may influence what sports we are naturally good at or whether we are fast or strong. Olympic athletes tend to fall into sports that match their genetic makeup. Olympic sprinters have been shown to possess about 80 percent fast twitch fibers, while those who excel in marathons tend to have 80 percent slow twitch fibers.” However, Quinn also gives links to journal articles that suggest intense training may alter the percentage of muscle type, so genetics aren’t the only factor.

The variability between individuals extends beyond the percentage of one muscle fiber type or the other; it seems that the number of muscles I have may be quite different from your count. (And complicating matters, expert opinions conflict over the exact number of muscles in the body—it’s more than 600—because in many cases there is no agreement on what constitutes a distinct muscle.) Nevertheless, according to one researcher, psychologist Bridget Waller of the Centre for the Study of Emotion at the University of Portsmouth in England, the number of facial muscles varies considerably between individuals. Read “Humans Have 5 Universal Facial Muscles—And 10 Optional Ones” by Susan Kruglinski in Discover magazine.

Searching for the lowdown on muscle differences between species on the Internet was frustrating; I couldn’t find a site that does a good job of comparing muscles across the animal kingdom. Oddly, the closest I came was a site at the Exploratorium in San Francisco on the Science of Meat. (On second thought, it’s not so strange, as meat is muscle.) Click on the “Inside the Meat” and “Comparative Muscle Chart,” and you will learn about the differences between fish, pork, beef, and chicken muscles. The different appearances of the meat are largely due to the distribution of slow- and fast-twitch muscles. There is no doubt that each species’ muscles are finely tuned to its lifestyle.I Googled whales and muscles and found an interesting site at the University of Wisconsin at River Falls: Whales How Low Can You Go? The Physiology of the Deep Diving Adaptations of Whales authored by Lisa Carlson, Amy Schuler, and Vanessa Smith. Scroll down to “Musculature” and “Respiration,” and you’ll learn that the animals’ special muscle tissue is one of the keys to deep diving. The myoglobin (oxygen-storing pigment in muscle) content in a whale’s muscle “is up to ten times higher than in terrestrial animals, so cetacean muscle is richer and darker in color due to the high oxygen content. During a dive, limited oxygen is shunted to vital organs, the heart, and the brain via the blood, but the muscles continue working using the oxygen supply stored in the myoglobin in the muscles. When the supply in the muscles runs out, a whale’s muscles work anaerobically.” Penguins and other marine animals that hold their breaths are similarly adapted. At another page from the Exploratorium, Ice Stories: Dispatches from Polar Scientists, scroll down to read how the emperor penguins can dive 1,800 feet and return to the surface twenty minutes later, all thanks to the oxygen stored in their muscle tissue.

Looking for interesting sites on the evolution of muscles, I came across a fascinating journal article titled, "Phylogenetic Relationship of Muscle Tissues Deduced from Superimposition of Gene Trees,” by Satoshi OOta and Naruya Saitou in Japan. They explored the evolution of muscle tissue by looking at the various myosin proteins, and found they could trace the origins of several of the muscle types. “Our results suggest that the emergence of skeletal-cardiac muscle type tissues preceded the vertebrate/arthropod divergence” some 700 million years ago. Read the abstract to learn about their other findings. Another article whose title, properly worded, is “Evolution of Trunk Muscles to Cope with Four Legs,” by Jorge M. O. Fernandes at the University of St. Andrews in the United Kingdom, describes the role of muscle evolution in the conquest of land some 350 million years ago. And last but not least, watch the National Geographic video above, which reports on a chance discovery that a genetic mutation altering a single jaw muscle may have triggered the expansion of hominid brains, 2.4 million years ago. We are what we are because of our muscles.


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