Taste and Olfaction detection of chemical substances food, poison, potential mates, predators, mark territory very old sensory systems. Japanese delicious 1.
Acids dissolve in water and generate hydrogen ions.
Vpm projects to som cortex, VMb projects to gustatory cortex Brodmann's area 43. Thus, food is not static. Selection for finely tuned receptors and system would not be good. Vmb extremely large in ungulates and monotremes not clear why echidna's have an extremely large tongue but more somatosensory and exploration. ORC are neurons and do have action potential.