1. Olfaction
The Sense of Smell

2. The nose knows!

3. Smell helps us: Avoid dangerous situations (fumes, smoke)
Avoid consuming poisonous substances and spoiled food (sour milk)
Choose mates?

4. What are olfactory stimuli?
Odorants (airborne molecules)
Odorants must be volatile (they give off vapors)
More vapors are given off when an odorant is heated!! (warm soup smells better than cold soup)

5. Odorants reach olfactory receptors by:
1. Being inhaled through the nose.
2. Through the mouth (vapors circulate up through throat)

6. The receptor in your nose catches the molecules in the air .
3,000 – 10,000

7. The “smell” receptors send information into your brain .

8. Olfaction- originates in the nasal cavity

9. Olfactory system structures

10. Olfactory Receptor Neurons
Carry impulses directly to the brain
Live for 5- 8 weeks & then die.

11. Summary: olfactory pathway
Scents travel through the nose or mouth and up to the Olfactory receptor neurons
Olfactory receptor neurons detect odorants in mucosa.
Signals are sent via olfactory receptor neurons to bulb structures (glomeruli).
Mitral and tufted cells carry signals to orbitofrontal cortex, temporal lobe, and the limbic system.

12. olfactory bulb - recoding
Olfactory Pathway
receptor cells
olfactory bulb - recoding
amygdala
hypo-thalamus
temporal lobe
thalamus

13. Which animal is most sensitive to smell?
Dogs ,000 times more sensitive to smell than humans
Why? Humans have million olfactory receptor neurons, dogs have over a billion!!

15. Ability to Detect Common Odors

16. Variations in Odor Sensitivity
Women have a better sense of smell than men.
The ability to smell diminishes with age. Smell acuity is greatest during early adulthood (ages 20-40).
People recall smells with 65% accuracy after a year, while visual recall is only about 50% after 3 months.

17. Anosmia: loss of sense of smell
May be to specific odors or all odors.
Caused by infection to nasal cavity or brain injury (frontal lobe).
About 2 million people in US are anosmic.

18. Olfaction and behavior
Babies enthusiastically “orient” to pleasant odors (banana, vanilla) and cry/grimace to unpleasant odors (shrimp; rotten eggs).
Babies can discriminate their mother’s scent from other women (Macfarlane, 1975).

19. Emotion Most universally-rated “pleasant” odorant is vanilla.
The perception of smell includes not only the odors themselves, but also the experiences and emotions associated with them.
Our Olfactory receptors are directly connected to the limbic system- the “seat” of emotion.
Most universally-rated “pleasant” odorant is vanilla.

20. Interestingly, differences in brain neurons activity in the left and right hemispheres have a relationship to the “pleasantness” of odors. Studies claim that positive emotions are predominately processed by the left hemisphere, and negative emotions in the right hemisphere.
Scents can affect our mood- Casinos pump “pleasant” scents into the gambling floor to promote spending!!!!!

21. Emotion & Attraction
Contrary to popular belief, women are NOT attracted to the natural body odor of male sweat! Pheromones are scents that our bodies produce naturally and do increase the attraction of males to females and females to males, However, sweat is not considered a “pleasant” odor.