The tongue, where the sense of taste is best developed, is marked by four types of bumps called lingual papillae (fig. 16.5a):

1. Filiform13 papillae are tiny spikes without taste buds. They are responsible for the rough feel of a cat's tongue and are important to many mammals for grooming the fur. They are the most abundant papillae on the human tongue, but they are small and play no gustatory role. They are, however, important to appreciation of the texture of food.

2. Foliate14 papillae are also weakly developed in humans. They form parallel ridges on the sides of the tongue about two-thirds of the way back from

13fili = thread + form = shaped

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Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Chapter 16 Sense Organs 593

Gustatory OrgansGustatory Organs

Chapter 16 Sense Organs 593

Location And Structure Tasted Buds

Figure 16.5 Taste (gustatory) Receptors. (a) Dorsal view of the tongue and locations of its papillae. (b) Detail of the vallate papillae. (c) Taste buds on the walls of two adjacent foliate papillae. (d) Structure of the taste buds.

the tip. Most of their taste buds degenerate by the age of 2 or 3 years.

3. Fungiform15 (FUN-jih-form) papillae are shaped somewhat like mushrooms. Each has about three taste buds, located mainly on the apex. These papillae are widely distributed but especially concentrated at the tip and sides of the tongue.

4. Vallate16 (circumvallate) papillae are large papillae arranged in a V at the rear of the tongue. Each is surrounded by a deep circular trench. There are only 7 to 12 of them, but they contain

15fungi = mushroom + form = shaped 1evall = wall + ate = like, possessing about half of all our taste buds—around 250 each, located on the wall of the papilla facing the trench (fig. 16.5b).

Regardless of location and sensory specialization, all taste buds look alike (fig. 16.5c, d). They are lemon-shaped groups of 40 to 60 cells of three kinds—taste cells, supporting cells, and basal cells. Taste (gustatory) cells are more or less banana-shaped and have a tuft of apical microvilli called taste hairs that serve as receptor surfaces for taste molecules. The hairs project into a pit called a taste pore on the epithelial surface of the tongue. Taste cells are epithelial cells, not neurons, but they synapse with sensory nerve fibers at their base. A taste cell lives 7 to 10 days and is then replaced by mitosis and

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Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

594 Part Three Integration and Control differentiation of basal cells. Supporting cells have a similar shape but no taste hairs. They lie between the taste cells.

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