Page 516 - Atlas of Histology with Functional Correlations

taste and to assist with mastication (chewing) and swallowing of the food

mass, called a bolus. In the oral cavity, taste sensations are detected by
receptor taste cells in the taste buds of the fungiform and circumvallate
papillae of the tongue. In addition to the tongue, taste buds are also found in
the mucous membrane of the soft palate, pharynx, and epiglottis.

Substances to be tasted are first dissolved in the saliva in the oral cavity

and then contact the taste cells by entering the taste pores. In addition to
saliva, taste buds located in the epithelium of circumvallate papillae are
continuously washed by secretions produced by the underlying serous (von
Ebner) glands. This secretion enters the furrow at the base of the papillae to

dissolve different substances, which enter the taste pores in taste buds. The
receptor taste cells are stimulated by direct contact with the molecules of
dissolved substances, which in turn stimulate the afferent nerve fibers with
which the taste cells synapse and conduct the information to the brain for

taste interpretation and detection. Fully tasting food requires olfaction in
addition to taste bud activation.

There are four basic taste sensations: sour, salt, bitter, and sweet. A fifth
type of taste, called umami (savory), is sensed by receptors for glutamate,

found in salt form as monosodium glutamate. All remaining taste sensations
are various combinations of the basic four tastes. It is now believed that the
sensitivity to all tastes is equally distributed across the entire tongue.
However, it is also believed that some areas of the tongue may be more
sensitive to a certain specific type of taste than to others.

FIGURE 13.10 | Posterior Tongue: Behind

Circumvallate Papilla and Near Lingual Tonsil

(Longitudinal Section)

The anterior two thirds of the tongue are separated from the posterior third of the
tongue by a depression or a sulcus terminalis. The posterior region is located

behind the circumvallate papillae and near the lingual tonsils. The dorsal surface
of the posterior region exhibits large mucosal ridges (1) and elevations or folds
(7) that resemble the large fungiform papillae of the anterior tongue. A stratified
squamous epithelium (6) without keratinization covers the mucosal ridges (1)

and the folds (7). The filiform and fungiform papillae of the anterior region of
the tongue are absent from the posterior tongue. Lymphatic nodules of the

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