Smell (Olfaction)

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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 5 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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Whats 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 receptors which the
  brain then interprets (like typing individual
  letters to make up a word).

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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 10 million for humans.
• Anosmia condition where a person cannot smell
  certain substance or cannot smell at all.

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The Olfactory Brain
Information from the taste buds (orange arrow)
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 (red arrow) also
connects with areas involved in memory storage,
which helps explain why a smell can trigger a
memory explosion.