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Smell�(Olfaction)

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Smell (Olfaction)

  • Smell is a chemical sense.
  • You inhale something of whatever of whoever it is you smell.
  • You smell something when molecules of a substance reach a tiny cluster of 20 million olfactory receptor cells at the top of each nasal cavity.
  • These olfactory receptor cells, wave back and forth responding to certain molecules and instantly alert the brain through axon fibers that make up the olfactory nerves. (These are constantly being replaced every 30 to 60 days.)

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The Process of Smell (continued)

  • Olfactory nerves directly connect to the olfactory bulb at the front of the brain.
  • Neural pathways lead out from here forming the olfactory tract which connect it to the temporal lobe (conscious recognition of smells) and to the limbic system (emotional responses to smells).
  • Notice this does not go to the thalamus like other senses. Instead it goes directly to your brain!

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What’s that Smell?

  • We have about 1000 receptor proteins used for detecting particular odors.
  • These combine to let us detect 10,000 different odors.
  • A particular odor activates a specific combination of different receptor proteins which the brain then interprets (like typing individual letters to make up a word).

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Smell

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Smell

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Smell

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The Olfactory Brain

  • Information from the taste buds travels to an area of the temporal lobe not far from where the brain receives olfactory information, which interacts with taste.
  • The brain's circuitry for smell also connects with areas involved in memory storage, which helps explain why a smell can trigger a memory.

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Facts about Olfaction

  • Odors evoke memories and feelings because they are tied to the limbic system (primitive areas of the brain that deals with emotion).
  • Sensory adaptation for odors occurs within a minute as we become about 70% less sensitive to it.
  • Women have a better sense of smell than men.
  • Olfactory function decreases with age especially after age 65 (half report this) and then again at age 80 (3/4 report this).
  • Loss of smell can occur due to pollution but also to Parkinson's, schizophrenia, multiple sclerosis and Alzheimer's.
  • Difficult to identify smells verbally.
  • Other animals use smells to identify or navigate. Dogs have 200 million olfactory receptor cells compared to 20 million for humans.
  • Anosmia – condition where a person cannot smell certain substance or cannot smell at all.

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