Taste and flavour sensation

If one compares the five special senses it can evidently be noticed that taste is a relatively crude sense. Only four basic tastes can be distinguished, sweet, sour, salty, and bit- ter. Nevertheless) some additional flavours can be determined because of the combination of sense of taste with a sense of olfaction (smell). Tasting occurs in the mouth where the longue is lodged. The tongue is covered with a series of small projections called papillae that contain cells (gustatory receptors, taste buds) sensitive to the chemical nature of food. We have some ten thousand of them. Gustatory cells are marked by the shortest life cycle among the epithelial cells of the body. Every two hundred and fifty hours, on the average, every cell is replaced by a younger one moving from periphery to the center.

There are two types of papillae: large fungiform papillae and small filiform papillae. Fungiform papillae occur in small num­bers at random over the tongue surface, mainly in the middle. Filiform papillae occur in large numbers over all except the back of the tongue’s upper surface, and on the palate. Papillae are located not only in the tongue but also in posterior wall of pharynx, soft palate, tonsils and epiglottis. Most numerous taste buds can be found on the tip, front part of the tongue and its sides. Less numerous they are on the rear part. Such sub­stances as salt, sugar, lemon juice and quinine (salty, sweet, sour, and bitter substances accordingly) can normally be tasted if they are dissolved either in saliva or in any watery solution. Otherwise the substances cannot be detected by taste buds.

Receptors for taste carry information on the character and concentration of substances entering the mouth. Their exci­tation triggers a complex chain of reactions in various brain parts. As a result, different alimentary organs are set to work and harmful substances getting into the mouth are removed.

It was proved that there exist special taste centers on the tongue. They are responsible for the main four types of taste.! Taste buds sensitive to sweet substances find place on the tip and front of the tongue. Gustatory receptors sensitive to salty chemicals are dispersed laterally, along the sides of the tongue. The rear part of the tongue is responsible for bitter tasting. Sour chemicals can be detected at the proxi­mal sides on the front of the tongue. The chemicals stimu­late hairs projecting from the receptor cells to cause taste sensation signals. Those are sent from the cells along fibers running in the facial and glossopharyngial nerves to taste centers in the parietal lobes of the brain.

Task 24. Learn the medical terms. They may come handy in your reports on gustation process:

taste bud — any of the cells embedded principally in the epithelium of the tongue and functioning as the sense or­gans of taste

taste cell — a neuroepithelial cell that is located in a taste bud and is the actual receptor of the sensation of taste i (called also gustatory cell) taste hair — the hairlike free end of a neuroepithelial cell in a taste bud

flavour — the blend of taste and smell sensations evoked by a substance in the mouth; the quality of something that affects the sense of taste gustation — the act or sensation of tasting gustatory (nerves) — nerves relating to gustation (vagus nerve, nervus vagus, nervus glossopharyngeus, nervus facialis)

Task 25. Study the new words that you will come across in the further given text “Touch and Somatosensory Per­ception”. Their pronunciation presents some difficulties too. Pronounce them correctly before you come to nar­rating of the text:

acknowledge [3k'nolid3] — визнавати; усвідомлювати;