X vagus nerve branches to throat greater superficial petrosal nerve also goes to soft palate Taste buds contain receptor cells. Papillae may have many buds. Cells contact oral fluids via hairlike cilia - protrude through pores.
Individual differences are important - e.g. PTC dimorphism.
Theories of sourness sour - hydrogen ions from acids, tartaric and malic, citric, acetic, lactic. Given a 5mM solution of HCl, it takes 64mM acetic acid to evoke an equal response from rat taste nerves. The relative pH of the two solutions is 2.3 and 3.0.