How Does a Muscle Work?
Credit: Mark McGowan, Pat Murphy, David Goodsell, Leana Rosetti

What ties life forms together? Visitors to the Exploratorium in San Francisco, California, discover that life has four basic traits: Life needs energy; all life shares common materials; life creates more life, and life changes over time. Unveiled in 2003, the "Traits of Life" exhibit has been hugely popular, even spawning a traveling road show. This poster sprang from the drive to provide examples of the ways in which life uses energy. Geared toward high school students, it explains the cycle that muscles use to "turn energy into motion." Graphic designer Mark McGowan, scientific illustrator David Goodsell, and their Exploratorium colleagues use the example of gripping a baseball to explain how muscles work. Zooming in on a chunk of hand muscle with a magnification power of 200,000, the exactly scaled poster shows how club-headed molecules of myosin use energy from ATP to repeatedly grab long filaments of actin and drag them toward each other "like a ship's crew pulling a rope hand over hand." Repeated trillions of times in all the muscle fibers of the hand, the result is a baseball that doesn't fall to the floor.