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Olefaction

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Smell

• Chemical detection without the danger of ingesting poison

• Object identification

• Sexual signaling

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Nasal Anatomy

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Nasal Anatomy• Nasal cavity - Hollow portion of head behind nose -

warms air, filters out dust, houses the sense of smell• Olfactory epithelium - Area of nasal cavity with

olfactory receptors

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Nasal Anatomy• Receptors are genuine neurons (unlike photoreceptors and

hair cells)• Unlike other neurons, receptors are continually regenerated• 1,000 different receptor types - about 1% of your DNA

codes for olfactory receptors making it the largest single gene family

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Olfactory Epithelium

• Receptors have four parts cilia, olfactory knob, olfactory rod and the axon

• Olfactory nerve - the axons of the olfactory receptors form bands which travel to the olfactory bulb

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Olfactory Bulb

• Olfactory bulb - organ which houses all the nerves which receive inputs from the olfactory receptors (mitral cells and periglomerular cells)

• Limbic and Thalamic connections

• Olfactory cortex (frontal lobe)

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Early Olfactory Pathway

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Central Olfactory Pathways

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Central Olfactory Pathways

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Central Olefactory Pathways

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Central Olefactory Pathways

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Central Olefactory Pathways

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Central Olefactory Pathways

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Perception of Smell

• The dimensions of smell

Flowery

Foul

Fruity

Spicy

Burnt

Resinous

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Perception of Smell (cont.)

• We can distinguish between about 10,000 different smellsDifferent threshold levels for different smells

• Two thresholds for each smell -low threshold for the existence of a chemical, somewhat higher threshold to discriminate one smell from another

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Perception of Smell (cont.)

• Adaptation - Olfactory fatigue - cross-adaptation

• Smell Constancy - receptors are more stimulated during a deep sniff than a shallow one - the judgment of odor intensity does not change -

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Perception of Smell (cont.)

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Pheromones: MammalsPowerful effects on behavior, specifically sexual

behavior, territorial behavior and identification of kin

Mammals• Most mammals only become sexually aroused in the

presence of pheromones• Increased likelihood of pregnancy• Synchronization of estrus cycles• Mutual recognition of mother and offspring• Territory marking (e.g. dogs)

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Pheromones: Mammals• Releasers - trigger a specific behavioral response • Primers - trigger a hormone response which increases

the likelihood of certain types of behaviors

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Pheromones: HumansHumans • infants can correctly identify their own mother's milk

and are much more likely to nurse when its their own mother

• female menstrual cycles can be altered by pheromones - the sorority effect

• male and female behavior is highly influenced by pheromonest-shirt experiment - musky versus sweet -

• the musky odor is rated by males and females as unpleasant and is thought to serve as a territorial marker among males

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Pheromones: Alpha Androstenolalpha androstenol (predominantly secreted by females)

1. Increase sexual arousal in males

2. Increases male perception of female attractiveness

• women in photographs were rated as significantly more sexually attractive when

judges were first exposed to alpha androstenol

3. Increases willingness of females to initiate social contact with males

• females exposed to alpha androstenol were much more receptive to male-initiated

contact

• more likely to seek out male company

• less likely to seek female company