Have you ever stopped to wonder how the different foods that you eat are perceived as different tastes? Taste is one of five senses that humans share, and one of three chemical senses. The entire process begins as food enters the mouth. Within the mouth, the average human has approximately ten thousand taste buds. As majority of these are found on the tongue, it is important to know that there are also numerous located underneath the tongue, on the inside of the lip, inside the cheeks and on the roof of the mouth. Before the chemicals of the food can be assessed, the food must first be broken down into its simplest chemical compounds. This job is taken on by saliva. A secretion of alkaline water by the salivary glands, saliva is made up of splitting enzymes such as amylase that help to start the breakdown of food into smaller chemical compounds, and then carry them to the taste buds. As commonly assumed, it is not the red bumps on the tongue that you would expect to be taste buds that are stimulated, it is the sixty to one hundred receptors found within each single bump that are stimulated. Since different compounds form different molecular shapes, only certain chemicals can fit into certain receptors which stimulate specific senses. Primarily, there are five principal tastes; sweet, bitter, sour, salty and umami. Each of the five are stimulated by different receptors and as a super generalization, each tend to be located in different general areas of the tongue, but in reality can be found anywhere. As can be interpreted from the picture on the left, bitter is perceived from receptors at the back, sour is perceived from receptors on the back sides, salty is perceived from receptors on the sides near the front, and sweet is perceived from receptors of the tip of the tongue. Following the linking of the chemicals to different receptors and through different ion channels, the tongue translates the chemicals into a neural code, as synaptic activation of neurons sends information to the brain by peripheral gustatory neurons. After reaching the brain, the stimuli are then detected and interpreted by the gustatory and parietal cortex and a feedback loop occurs while the individual either senses disgust or pleasure. However, only substances that are fat or water soluble can stimulate receptors because they must be in liquid or solution for the tastant to have the ability to respond with its receptor. As a result, something that is not dissolved in to saliva will not be tasted.
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