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Five facts about smell

Alice Bartlett
November 02, 2013

Five facts about smell

Five facts about smell squeezed in to 10 minutes.

I had so much fun giving this talk. There is a mistake on slide 15 which I have left in for the lols.

Alice Bartlett

November 02, 2013



  2. 1. Humans have three chemical senses.

  3. 1. Taste 2. Smell 3. Trigeminal

  4. 2. 1.2% of people do not have a sense of

    smell*. [Gilbert and Wysocki 1987]
  5. *I am one of those people. Hello.

  6. 3. Some smells are easily detectable to humans even at

    very low concentrations. Nobody knows why.
  7. **SUB-LIST TIME**


    3. BUTTER 4. PEPPERONI 5. STRAWBERRY [Ohloff 1990]
  9. FIVE SMELLY SMELLS: ! Nobody knows why the human nose

    is better at detecting these compounds but it really is.
  10. Comparison of detection thresholds in water: ! Limonene: 10ppb 

    ! Menthene-8-thiol: 0.00001ppb (grapefruit) Demole E., P Enggist and G. Ohloff, Helv. Chem. Acta, 65, 1785-1794 (1982) (limonene)Fazzalari, F A., editor, Compilation of Odor and Taste Threshold Data, ASTM Data Series DS 48A (1978)
  11. TODAY YOU LEARNT: ! Grapefruits are 1 million times smellier

    than lemons*. *kinda
  12. 4. There are seven primary smells

  13. These classifications are more psychological than chemical but are very

    handy for talking about smells.
  14. **SUB-LIST TIME**

  15. SEVEN PRIMARY ODOURS: ! 1. Musky (moth balls) 2. Floral

    (roses) 3. Pepperminty 4. Ethereal (detergent) 5. Pungent (vinegar) 6. Putrid (bad eggs) [Amoore et al. 1964]
  16. 5. We don’t really know how humans detect smell.

  17. The facts:

  18. You have between five and six million smell receptors

  19. You have 347 different types of olfactory receptor.

  20. One olfactory receptor will detect several (similar) molecules and react

    with different intensities to them.
  21. Your olfactory receptors seem to react in a combinatorial way.

    [Buck et al. 1999]
  22. The problem

  23. We don’t know how this reaction works. There are two

    theories and neither have been disproven
  24. “Shape Theory” states that molecules fit into receptors like a

    lock and key.
  25. This makes sense intuitively and is the historically preferred theory

  26. BUT

  27. Whilst shape theory works for most compounds, there are some

  28. Some compounds with vastly different shapes smell the same

  29. And some compounds with very similar shapes smell totally different

  30. This model has also not been able to predict any

    smells from looking at the shape, which you would expect it to be able to.
  31. “Vibration Theory” states that it is not the shape but

    the vibration pattern of the molecule that determines it’s odour
  32. This would explain why two compounds with different shapes can

    smell the same.
  33. But there are still challenges.

  34. Whilst some compounds with the same vibration energy smell the

    same, some smell different!