Taste Receptors

There are four types of taste receptors: (1) sweet, as produced by table sugar; (2) sour, as produced by vinegar; (3) salty, as produced by table salt; and (4) bitter, as produced by caffeine or quinine. Each of these taste receptors is most highly concentrated in certain regions of the tongue's surface. "Sweet receptors" are mostly on the tip of the tongue (noted in a child's preference to lick a candy sucker rather than chew it). "Sour receptors" occur primarily along the sides of the tongue and are stimulated mainly by acids. "Salt receptors" are most common in the tip and upper front portion of the tongue. They are stimulated mainly by inorganic salts. "Bitter receptors" are located toward the back of the tongue. They are stimulated by a variety of chemical substances, most of which are organic compounds, although some inorganic salts of magnesium and calcium produce bitter sensations too.