At first glance, nerve cells would appear to be energy hogs. The brain accounts for only about two percent of a human’s body mass, but burns through 20 percent of its energy budget. But transmitting signals by nerves is a multistep process, and it hasn’t been clear which step burns through the most energy. This isn’t a purely academic question: entire fields of study use PET scans and functional MRI imaging to track areas of the brain that are using energy, under the assumption that these are the most active. Now, researchers have followed the progress of impulses down a nerve fiber, and determined that the process is remarkably efficient, using only about 30 percent more than the idealized lower limit of energy use.
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