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16.5: Taste Anatomy

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    53760
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    Taste Anatomy

    The primary tastes detected by humans are sweet, sour, bitter, salty, and umami. The first four tastes need little explanation. The identification of umami as a fundamental taste occurred fairly recently—it was identified in 1908 by Japanese scientist Kikunae Ikeda while he worked with seaweed broth, but it was not widely accepted as a taste that could be physiologically distinguished until many years later. The taste of umami, also known as savoriness, is attributable to the taste of the amino acid L-glutamate. In fact, monosodium glutamate, or MSG, is often used in cooking to enhance the savory taste of certain foods. What is the adaptive value of being able to distinguish umami? Savory substances tend to be high in protein.

    Anatomical model of a tongue with structures labeled

    Above: Structures of the tongue.

    Detecting a taste (gustation) is fairly similar to detecting an odor (olfaction), given that both taste and smell rely on chemical receptors being stimulated by certain molecules. The tongue is a crucial organ in mechanical digestion and taste. Taste buds contain taste receptor cells which are the smallest functional unit in gustation. Taste buds can be found throughout the length of the upper digestive tract. On the surface of the tongue are protrusions called papillae. Circumvallate papillae are arranged in a v-shape pattern on toward the base of the tongue, on the dorsal aspect, and contain more than 100 taste buds each. The fungiform papillae are found all over the dorsal aspect of the tongue and contain only about 5 taste buds each. The foliate papillae are found on the lateral aspects of the tongue and only contain taste buds during childhood. Finally, there are the filiform papillae which, like the fungiform papillae, are found all over the tongue, however, they do not contain taste buds. Instead, their barbed shape provides the friction for moving food around during mastication.

    Chemical are detected by gustatory cells in taste buds in the papillae of the tongue that relay these sensory signals to neurons in cranial nerves VII, IX, and X (facial nerve, glossopharyngeal nerve, and vagus nerve, respectively). Each taste bud’s taste cells are replaced every 10 to 14 days. These are elongated cells with hair-like processes called microvilli at the tips that extend into the taste bud pore. Food molecules (tastants) are dissolved in saliva, and they bind with and stimulate the receptors on the microvilli. The receptors for tastants are located across the outer portion and front of the tongue, outside of the middle area where the filiform papillae are most prominent.

    Diagram of the cells of a taste bud. oral cavity, lingual epithelium, connective tissue, taste pore, gustatory cell, basal cell, afferent nerve

    Above: Diagram of the microscopic anatomy of a taste bud. Many taste buds are present within papillae of the tongue.

    Taste neurons project from taste cells in the tongue, esophagus, and palate to the medulla, in the brainstem. From the medulla, taste signals travel to the thalamus and then to the primary gustatory cortex. Information from different regions of the tongue is segregated in the medulla, thalamus, and cortex.


    This page titled 16.5: Taste Anatomy is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Rosanna Hartline.

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