A cross-section of skeletal muscle in this light micrograph shows the individual, parallel muscle fibers (red). These fibers work in concert to power movement. Thomas Deerinck, NCMIR/ScienceSource hide caption

itoggle caption Thomas Deerinck, NCMIR/ScienceSource

False-color transmission electron micrograph of a field of whooping cough bacteria, Bordetella pertussis. A. Barry Dowsett/Science Source hide caption

itoggle caption A. Barry Dowsett/Science Source

This mouse egg (top) is being injected with genetic material from an adult cell to ultimately create an embryo — and, eventually, embryonic stem cells. The process has been difficult to do with human cells. James King-Holmes/Science Source hide caption

itoggle caption James King-Holmes/Science Source

It's the Sichuan peppercorn in dishes like spicy ma po tofu that makes your mouth buzz. Researchers wanted to know if that buzz is connected to the tingling you feel when your foot falls asleep. iStockphoto hide caption

itoggle caption iStockphoto