Sunday, December 20, 2009

Why do candy canes taste cool?

Candy canes and other mints taste cool because they contain menthol, which can bind to, and activate receptors that normally sense cold.  The fibers at the end of temperature sensitive nerve cells extend to just beneath the surface of your skin, and are also found in your tongue and throughout the inside of your mouth.  At the ends of these cells, there are ion channels which are basically hollow tubes made up of proteins.  At normal temperatures, these tubes are sort of scrunched up so that some of the proteins in the tube block the opening.  At colder temperatures, the tube straightens out and allows ions outside of the nerve cell to pass into the inside of the cell. 

These positively charged ions (sodium and calcium) flood into the cell when the receptors are open, and they change the electric potential across the cell membrane which in turn starts an action potential: a wave of electric current that moves along the length of the nerve cell (I've talked about action potentials and how nerve cells send information before here).  The action potential from a temperature sensitive neuron ultimately sends a signal all the way up to the brain which interprets this signal as cold.  What is interesting about these cold-sensing ion channels is that they can also be opened up when molecules bind to them at sites on the outside of the cell called receptor sites. In the case of our cold receptors, molecules like menthol (which is found in mint leaves, and thus in mint candies like candy canes) bind to the receptor site and cause the protein tube to open up.  This causes the action potentials and signaling we just talked about, which tell your brain that your tongue is cool when really it is just enjoying a candy cane at your normal body temperature.  Interestingly, this is very similar to what happens when you eat spicy foods that taste "hot", except in that case they are different receptors that open when heated (and close when cooled).  These "hot" receptors also open when bound by molecules, in this case, the most prominent one is called capsaicin (which is found in most hot peppers and hot sauces).  So,now you know why candy canes taste cool, and hot sauce tastes hot. (If your holidays are anything like mine, you are probably going to be eating candy canes and Buffalo wings at some point, though hopefully not at the same time).  Happy Holidays!

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