It's Rude To stick your Tongue Out

A Study of Gustatory Dominance

Background Information

Navigation Intro/Rationale Materials Procedure The Results Conclusion Bibiography

Taste is one of two chemical senses. The other is smell. Chemical senses are unique in that they react to molecules and groups of molecules in the air and in food we ingest. These senses are neurologically connected to systems in the brain which represent feeling states and certain memories. There are four commonly known tastes. These include sweet, sour, salty, and bitter. Hans Henning demonstrated in 1927 that most flavours can be achieved by combining these four taste qualities. However it was recently discovered that there is a fifth taste, umami. It is the savoury flavour found in seaweed. Gustatory receptors are found primarily on the tongue, but also in other areas of the mouth. Receptors are responsible for translating molecules into taste signals. Receptors are found in taste buds, which are in turn found in papillae. Papillae are the bumps that can be felt on the surface of the tongue. Each papillae has many taste buds and each taste bud contains as many as 50 receptors. Receptors are stimulated when the proper molecule binds to them. There are different receptors for each of the five taste qualities. Receptors for different qualities are not spread evenly about the tongue. The sweet receptors are found primarily on the tip of the tongue. Sour receptors can be found along the sides of the tongue. Salty receptors overlap from the sour area into the sweet. Receptors for bitter tastes are concentrated at the back of the tongue. There is no known area for umami. A map of the tongue. Taste receptors transfer their information to the brain via nerve fibres. Each nerve fibre branches off to receive information from many different taste buds. Fibres for the anterior two thirds of the tongue are a part of the chorda tympani, which is part of the facial nerve, or cranial nerve VII. The back of the tongue sends its messages through the lingual branch of the glossopharyngeal nerve, or cranial nerve IX. Finally, taste receptors from the back of the throat send their messages along the superior laryngeal branch of the vagus nerve, or cranial nerve X. Unlike other sensory systems the gustatory system travels unilaterally to the brain. This means that information from the left side of the tongue goes to the left side of the brain and information from the right goes to the right side of the brain. In contrast, messages from the hands or feet (sense of touch) switch sides as they travel to the brain. An illustration of the neural connections between the brain and the tongue. The limbic system is not shown. (Adapted From Kandel and Schwartz, 1985.) Messages from the taste receptors follow many different pathways. All of these paths lead first to the solitary nucleus in the medulla. From this point there are two main pathways. The first goes up into the thalamus, where messages are split into taste and touch sensations. The gustatory information is then sent to two different areas in the cortex. These are the postcentral gyrus and the insula. Both of these identify the flavours. The second pathway takes the same information to the parabrachial nucleus in the pons. From here it travels to the hypothalamus and the limbic system. This system has to do with the emotional qualities of taste.