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Olfaction The Sense of Smell. Smell helps us: Avoid dangerous situations (fumes, smoke) Avoid dangerous situations (fumes, smoke) Avoid consuming poisonous.

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Presentation on theme: "Olfaction The Sense of Smell. Smell helps us: Avoid dangerous situations (fumes, smoke) Avoid dangerous situations (fumes, smoke) Avoid consuming poisonous."— Presentation transcript:

1 Olfaction The Sense of Smell

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

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

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

5 Olfaction- originates in the nasal cavity

6 Olfactory system structures

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

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

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

10 Odor Hedonics What are “pleasant” and “unpleasant” odors? Variability is high. What are “pleasant” and “unpleasant” odors? Variability is high. Most universally-rated “pleasant” odorant is vanilla. Most universally-rated “pleasant” odorant is vanilla.

11 How is perception affected by odor? Odor enhances our experience of the world (food, surroundings, people). Odor enhances our experience of the world (food, surroundings, people). We associate memories with certain odorants. We associate memories with certain odorants. We lose the ability to experience “flavors” if our sense of smell is impaired. We lose the ability to experience “flavors” if our sense of smell is impaired.

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

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

14 Olfaction and Behavior B. Smell may alter hormonal activity B. Smell may alter hormonal activity McClintock Effect: women’s menstrual cycles synchronize when they live together (dorms). McClintock Effect: women’s menstrual cycles synchronize when they live together (dorms).

15 Olfaction and behavior C. Mate Selection C. Mate Selection Females rate males with immunity profiles more dissimilar to their own (Wederkind et al., 1995) as smelling “more pleasant.” Males with very similar immunity profiles are rated as smelling “less pleasant.” Females rate males with immunity profiles more dissimilar to their own (Wederkind et al., 1995) as smelling “more pleasant.” Males with very similar immunity profiles are rated as smelling “less pleasant.” What is the current theory underlying this finding? What is the current theory underlying this finding?

16 Smell may provide a clue about our suitability as a mate? It’s possible that choosing a mate with an immunity profile very similar to our own, may result in the expression of unwanted recessive genes in our offspring. It’s possible that choosing a mate with an immunity profile very similar to our own, may result in the expression of unwanted recessive genes in our offspring. Smell may provide us with a “cue” in which we can detect suitable mates who will produce healthy viable offspring. Smell may provide us with a “cue” in which we can detect suitable mates who will produce healthy viable offspring.


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