Posted May 4, 2011 at 2:10pm
Food is one of the things that I enjoy immensely. Everything just tastes so different from everything else. So how exactly does that work? How can bananas taste so differently than a steak? And how can the brain distinguish between the two?
The tongue is covered with taste buds, and these allow us to sense the different tastes in food when we eat them. These taste buds are chemoreceptors, which are sensory receptors that detect certain chemical stimuli in the environment and convert it into a useable form within the body. This means they translate the chemical signals that food produce when in contact with the taste buds into an electrical signal that can be sent though the body. These electrical signals are called action potentials, and they travel to the brain through the nervous system. When the signal gets to the brain it is identified by the brain and a certain sensation is experienced.
There are five different distinct tastes that the taste buds detect: salty, sweet, bitter, sour, and savory. When food enters the mouth, saliva breaks the food down into ions and other chemical molecules that then enter the pores of the taste buds. Each of these tastes is sensed by the taste buds a little bit differently, based on what molecules the food is broken down into.
Salty and sour tastes are sensed through ion channels that are triggered by ions, or electronically charged particles, that are found in salty or sweet foods. Salty foods contain the ion sodium chloride (NaCl), which is commonly called table salt. This molecule is composed of two ions: the positively charged sodium ion and the negatively charged chlorine ion. When the ions are being sensed, the sodium ion triggers the ion channels in the taste buds, which changes the electrical charge of the taste bud cells, causing an action potential. For sour foods, which contain acids, the positively charged hydrogen ions cause the action potential within the taste buds.
Bitter, sweet, and savory foods are sensed through G-protein coupled receptors, which are a more sophisticated mechanism than the ion channels, and one that is not well understood. Compounds within bitter and sweet foods trigger G-protein coupled receptors to release a messenger protein, gustducin, which triggers molecules to close potassium ion channels, creating an action potential. Sensing savory foods is similar, though it is triggered by the amino acid L-glutamate.
Once the action potential has been created and a signal has been sent through the nervous system, the signal is transferred between nerve cells until the signal reaches the brain where the signal is translated into a taste. The process from ingesting food to having a sensory experience from that food is very fast, happening within a couple of milliseconds, which is good because there are lots of delicious foods out there to try. And the tongue contains an average of 10,000 taste buds that get replaced every two days. That’s a lot of taste buds! Now it’s time to get busy using some!
