Pain is one of the more complex perceptions. Sensory neurons in the eye or the ear need detect only a single type of stimulus, such as light or sound. But pain-sensing neurons must detect more diverse stimuli, including heat, cold, acid, and mechanical pressure. To do this, they send out a complex web of sensory fibers, ending in specialized nerve endings known as nociceptors. Although nociceptors have been known about for more than a century, only in the last decade have researchers identified the specific ion channels that respond to noxious, potentially tissue-damaging stimuli. This is our "first molecular insight into the detection of stimuli under normal, acute pain conditions," says David Julius, of the University of California, San Francisco, whose group discovered transient receptor potential V1 (TRPV1), one of the first channels implicated in nociception.