The Fascinating World of Smell: From Olfaction to Pheromones

1. Olefaction Anthony J Greene

2. Smell • Chemical detection without the danger of ingesting poison • Object identification • Sexual signaling Anthony J Greene

3. Nasal Anatomy Anthony J Greene

4. 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 Anthony J Greene

5. 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 Anthony J Greene

6. 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 Anthony J Greene

7. 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)

8. Early Olfactory Pathway Anthony J Greene

9. Central Olfactory Pathways Anthony J Greene

10. Central Olfactory Pathways Anthony J Greene

11. Central Olefactory Pathways Anthony J Greene

12. Central Olefactory Pathways Anthony J Greene

13. Central Olefactory Pathways Anthony J Greene

14. Central Olefactory Pathways Anthony J Greene

15. Perception of Smell • The dimensions of smell Anthony J Greene

16. 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 Anthony J Greene

17. 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 - Anthony J Greene

18. Perception of Smell (cont.) Anthony J Greene

19. Pheromones: Mammals Powerful 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)

20. Pheromones: Mammals • Releasers - trigger a specific behavioral response • Primers - trigger a hormone response which increases the likelihood of certain types of behaviors Anthony J Greene

21. Pheromones: Humans Humans • 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

22. Pheromones: Alpha Androstenol alpha androstenol (predominantly secreted by females) • Increase sexual arousal in males • Increases male perception of female attractiveness • women in photographs were rated as significantly more sexually attractive when judges were first exposed to alpha androstenol • 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 Anthony J Greene