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The Sense Of Smell


									The Sense Of Smell
                     Smelly Facts
• Taste is 75% smell
• Moths can identify a single molecule among others by its smell
• Dogs can distinguish non-identical
  twins by smell, but not identical ones
• A smell can trigger very strong memories
• You cannot “imagine” a smell
• Dogs can smell cancerous tumors in people

• Women have a keener sense of smell than men do.
• By simply smelling a piece of clothing, most people can tell if a
  woman or a man had been wearing it.
• Each of us has an odor that is unique, just like our fingerprints.
• According to some sources, the stethoscope was invented not to
  hear the heartbeat better, but to give doctors some distance from a
  patient's bodily odors.
               More Smelly Facts
• Much of the thrill of kissing comes from smelling the unique odors of
  another's face.
• Smells stimulate learning. Students given olfactory stimulation
  along with a word list retain much more information and remember it
• Many smells are heavier than air and can be smelled only at ground
• We smell best if we take several short sniffs, rather than one long
• Dogs have 1 million smell cells per nostril and their smell cells are
  100 times larger than humans are.
• Humans use insect warning/attraction chemicals, called
  pheromones, to keep away/attract pesky insects.
• People who cannot smell have a condition called Anosmia.
• The smells of a rose,
  perfume, freshly baked bread
  and cookies...these smells
  are all made possible
  because of your nose and
• The sense of smell is called
• All the nose parts involved in
  smelling are the olfactory
   The Olfactory Apparatus
         Some vocabulary terms you ought to know . . .

          Olfactory epithelium
• The olfactory epithelium is a specialized
  tissue inside the nasal cavity that is involved in
   – In humans, it is about the size of a postage stamp
• The olfactory epithelium is a patch of tissue
  covered with receptor cells that detect odor
  molecules that you breath.
   – The smell equivalent of rods and cones
• Olfactory bulb: A key part of the olfactory
  apparatus, located on the under surface of the
  frontal lobe of the brain, just above the nasal
• Olfactory nerve sends smell signals to the
  olfactory bulb, a bulbous enlargement of the end
  of the olfactory nerve.
• Nerves then carry signals to the brain where you
  register the “scent.”
• We have two bulbs, so we smell in stereo!
              Frontal Lobe
• The part of each hemisphere of the brain
  located in the forehead that serves to
  regulate and mediate the “higher
  intellectual functions.”
• The frontal lobes have intricate
  connections to other areas of the brain.
• In the frontal lobes, we meld emotions,
  cognition, error detection, volition, a sense
  of self, and more to create our social brain.
 How Dose Your Olfactory
Apparatus Work Together to
     Create “Smell”?
Odor particles drift into your nose
and cause your smell receptors to
  send messages to your brain.
                       Olfactory Bulbs
  The smell part of the brain is in the
  limbic region, and is connected to
  the frontal lobe where feeling and
        memory are processed.
    Olfactory Bulb

Olfactory epithelium
When you breathe in through your nose, some of
  the air passes through to your olfactory
This tissue has millions of "receptor" cells in it, and
  each one is mounted on a microscopic hair that
  sticks out and waves in the air currents.
About forty of these cells must detect odor
  molecules before a smell is registered and sent
  to your brain.
A little on Taste…

Molecules of food stimulate the taste cells
to send messages to your brain.

The sweet and salty buds are the least
sensitive and the bitter ones are the most

                                   Taste bud
        More on Taste and Smell
• Humans basically taste four things:
  sweet, sour, salt and bitter.*
• It's the odors we can smell with our
  noses that make things really taste
• For example, chocolate’s odors, not
  its taste, are what make it delicious.
  With a head cold, drinking hot
  chocolate is an entirely different
• *In recent years a fifth taste has been
  recognized. This is umami, the
  protein flavor of monosodium
  glutamate. (Nature Genetics 25, 130
  - 132 (2000)
              Snuffy Nose
• When you have a cold
  and your nose is
  stuffed up, you cannot
  smell very well. This is
  because the
  molecules that carry
  smell cannot reach the
  olfactory receptors.
         Animals and Smell
• What do you feel when you smell male
  mouse urine?? (Depends who you are)

         Animals and Smell
• Nose size can tell you something about
  importance of smell to the organism.
Questions You May See on a Quiz
           or Test . . .
What is the evolutionary advantage to smelling
your environment? Can you think of an example
that relates to how Endler’s Guppies survived (or
failed to survive?)

In order, how do the components of the Olfactory
 Apparatus detect, say, a steak molecule?
    (Nose, Olfactory Epithelium, Olfactory Bulb,
 Frontal Lobe.)
• game/specimens/smell.html



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