Why might it be hypothesized that sour would be perceived more quickly than bitter or sweet?

Describe the pathway of taste reception from the point where food comes into contact with the tongue to the point at which taste information travels to the brain. Briefly describe the structure and function of each organ along the pathway.

Five different types of taste receptors have been identified in humans.  These are salty, sour, sweet, bitter and umami.  Taste receptors consist of specific types of proteins incorporated into the plasma membrane of taste receptor cells, which are clustered together in structures called taste buds.  All five receptor types are present in each taste bud, which are distributed over most of the tongue surface area.  Olfactory receptors are located in the nasal cavity and consist of several thousand different types, each type specific for a different odorant molecule (ligand).   If you plug your nose, red wine and coffee taste exactly the same.  Explain why this is so.