Narrator: This is Science Today. Why does a hot chili pepper feel hot and menthol feel cool? Dr. David Julius of the University of California, San Francisco, is a biochemist and molecular biologist who studies pain sensation and thermosensation, particularly by tracking how molecules such as capsaicin in chili peppers and menthol in mint leaves affect nerve fibers.
Julius: It activates an ion channel on the surface of certain types of nerve fibers in your skin and once this ion channel on the membrane is basically a pore on the membrane that opens up and allows ions to flow into the neurons. This movement of ions across the membrane generates an electrical signal which is the currency of communication in the nervous system and this initiates an electrical signal to the spinal cord and then from there, the information travels through a series of interconnected neurons to the brain so that you perceive this initial event of exciting the sensory neuron as a hot or a cold signal.
Narrator: For Science Today, I'm Larissa Branin.