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Five facts about smell

Alice Bartlett
November 02, 2013
420

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
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Transcript

  1. FIVE
    FACTS
    ABOUT
    SMELL
    BY @ALICEBARTLETT

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  2. 1. Humans have three
    chemical senses.

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  3. 1. Taste
    2. Smell
    3. Trigeminal

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  4. 2. 1.2% of people do
    not have a sense of
    smell*.
    [Gilbert and Wysocki 1987]

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  5. *I am one of those
    people. Hello.

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  6. 3. Some smells are
    easily detectable to
    humans even at very
    low concentrations.
    Nobody knows why.

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  7. **SUB-LIST TIME**

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  8. FIVE SMELLY
    SMELLS:
    !
    1. GRAPEFRUIT JUICE
    2. CORK ODOUR
    3. BUTTER
    4. PEPPERONI
    5. STRAWBERRY
    [Ohloff 1990]

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  9. FIVE SMELLY
    SMELLS:
    !
    Nobody knows why
    the human nose is
    better at detecting
    these compounds but
    it really is.

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  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)

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  11. TODAY YOU LEARNT:
    !
    Grapefruits are 1
    million times smellier
    than lemons*.
    *kinda

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  12. 4. There are seven
    primary smells

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  13. These classifications
    are more psychological
    than chemical but are
    very handy for talking
    about smells.

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  14. **SUB-LIST TIME**

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  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]

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  16. 5. We don’t really
    know how humans
    detect smell.

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  17. The facts:

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  18. You have between five
    and six million smell
    receptors

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  19. You have 347 different
    types of olfactory
    receptor.

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  20. One olfactory receptor
    will detect several
    (similar) molecules and
    react with different
    intensities to them.

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  21. Your olfactory
    receptors seem to
    react in a
    combinatorial way.
    [Buck et al. 1999]

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  22. The problem

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  23. We don’t know how
    this reaction works.
    There are two theories
    and neither have been
    disproven

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  24. “Shape Theory” states
    that molecules fit into
    receptors like a lock
    and key.

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

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  26. BUT

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

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  28. Some compounds with
    vastly different shapes
    smell the same

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

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  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.

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  31. “Vibration Theory”
    states that it is not the
    shape but the vibration
    pattern of the
    molecule that
    determines it’s odour

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  32. This would explain why
    two compounds with
    different shapes can
    smell the same.

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  33. But there are still
    challenges.

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  34. Whilst some
    compounds with the
    same vibration energy
    smell the same, some
    smell different!

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