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Olfaction. Objectives: Be able to. Define olfactory receptor proteins, glomeruli, and odotopes. Describe odorant transduction. Relate olfactory receptor proteins, receptor neurons, glomeruli, and odotopes to odor identification. Describe theories of olfaction.

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objectives be able to
Objectives: Be able to
  • Define olfactory receptor proteins, glomeruli, and odotopes.
  • Describe odorant transduction.
  • Relate olfactory receptor proteins, receptor neurons, glomeruli, and odotopes to odor identification.
  • Describe theories of olfaction.
  • Describe the major parts of any perfume and explain their functions.
  • Discuss memory for odors.
olfaction1
Olfaction
  • Olfactory Physiology
  • From Chemicals to Smells
  • Olfactory Psychophysics, Identification, and Adaptation
  • Olfactory Hedonics
  • Olfaction, Memory, and Emotion
olfactory physiology
Olfactory Physiology
  • Odors: Olfactory sensations
    • Chemical compounds
    • But not every chemical is odorant
    • In order to be smelled: Molecule must be volatile, small, and hydrophobic
olfactory physiology cont d
Olfactory Physiology (cont’d)
  • The human olfactory apparatus:
    • Primary purpose of nose: to filter, warm, humidify air we breathe
    • Nose: Small ridges, olfactory cleft, olfactory epithelium
slide14
(a) Two molecules with the same structure and different odor. (b) Two molecules with different structures but the same odor.
slide15

Olfactory Receptor Neuron Response to Two OdorsGray cells respond to odor 1, Dark outlined cells respond to odor 2, Two cells respond to both

olfactory physiology cont d1
Olfactory Physiology (cont’d)
  • The olfactory epithelium: the “retina” of the nose:
    • Three types of cells:
    • 1. Supporting cells
    • 2. Basal cells
    • 3. Olfactory sensory neurons (OSNs)— have cilia protruding into mucus covering olfactory epithelium
    • Olfactory receptors (ORs): Interaction between these and odorant stimulates cascade of biochemical events
discussion question 61
Discussion Question 61
  • Relate olfactory receptor proteins, receptor neurons, glomeruli, and odotopes to odor identification.
olfactory physiology cont d2
Olfactory Physiology (cont’d)
  • Olfactory loss can cause great suffering:
    • Sense of flavor (taste +)
    • Danger warning
olfactory physiology cont d3
Olfactory Physiology (cont’d)
  • Olfactory receptor cells are different from all other sensory receptor cells: They are not mediated by any protective barrier, make direct contact with brain.
    • (e.g., visual receptors are protected by cornea, receptors for hearing are protected by eardrum, taste buds are buried in papillae)
    • Therefore many drugs can be inhaled
    • OSN axons are among thinnest and slowest in body
    • Therefore it takes a long time to perceive odors compared to other perceptions
olfactory physiology cont d4
Olfactory Physiology (cont’d)
  • Subtle differences between sensation and perception:
    • Sensation occurs when scent is neurally registered
    • Perception occurs when becoming aware of detecting it
olfactory physiology cont d5
Olfactory Physiology (cont’d)
  • The genetic basis of olfactory receptors:
    • In 1991 Buck and Axel showed that genome contains about 1000 different olfactory receptor genes, each codes for single type of OR
    • Animals have fewer ORs
    • Trade-off between vision and olfaction
olfactory physiology cont d6
Olfactory Physiology (cont’d)
  • The feel of scent:
    • Odorants can stimulate somatosensory system through polymodal nociceptors (touch, pain, temperature receptors)
    • These sensations are mediated by the trigeminal nerve (cranial nerve V)
    • Often, it is impossible to distinguish between sensations traveling up cranial nerve I from olfactory receptors and those traveling up cranial nerve V from somatosensory receptors
from chemicals to smells
From Chemicals to Smells
  • Theories of olfactory perception:
    • Shape-pattern theory: Match between shapes of odorants and odor receptors; dominant biochemical theory
    • Recent molecular research: Scents are detected by means of combinatorial codes
    • Vibration theory: There is a different vibrational frequency for every perceived smell, molecules that produce same vibrational frequencies will produce same smell
from chemicals to smells cont d
From Chemicals to Smells (cont’d)
  • Specific anosmia:
    • The inability to smell one specific compound with otherwise normal smell perception
    • 50% of population has specific anosmia to androstenone
    • Change in detection can occur with training
    • This cannot be explained by vibration theory
from chemicals to smells cont d1
From Chemicals to Smells (cont’d)
  • Study of stereoisomers:
    • Molecules that are mirror-image rotations of one another; although they contain the same atoms, they can smell completely different
    • Vibration theory cannot explain this phenomenon
from chemicals to smells cont d2
From Chemicals to Smells (cont’d)
  • The importance of patterns:
    • How can we detect so many different scents if our genes only code for about 1000 olfactory receptors?
    • We can detect the pattern of activity across various receptor types
    • Intensity of odorant also changes which receptors will be activated
    • So weak concentrations of odorant do not smell the same as strong concentrations of it
    • Specific time order is important
from chemicals to smells cont d3
From Chemicals to Smells (cont’d)
  • Odor mixtures:
    • We rarely smell “pure odorants,” rather we smell mixtures
    • How do we process the components in an odorant mixtures
    • Two possibilities:
      • Analysis
      • Synthesis
from chemicals to smells cont d4
From Chemicals to Smells (cont’d)
  • Analysis: Example from auditory mixtures: high note and low note
  • Synthesis: Example from color mixtures: mixing red and green lights, resulting in yellow light
making perfume
Making Perfume
  • Perfumes have three types of ingredients:
  • Essential oils (that give you the smell of the perfume), pure grain alcohol, water.
  • The mixture of essential oils includes three types: Bass notes – not volatile, stay longest on the skin
  • Middle notes – less volatile, influence smell for a pretty long time; they drag the bass notes into the air.
  • Top notes-most volatile, short lasting, drag middle notes
perfume oils
Perfume Oils
  • Last, but not least, here’s a list of the most easily found oils that may lead you to your dream perfume:
  • 1. Bass notes – sandalwood, vanilla, cinnamon, mosses, lichens, ferns;
  • 2. Middle notes – lemongrass, geranium, neroli, ylang-ylang;
  • 3. Top notes – orchid, rose, bergamot, lavender, lemon, lime.
discussion question 62
Discussion Question 62
  • Describe the major parts of any perfume and explain their functions
from chemicals to smells1
From Chemicals to Smells
  • Odor imagery:
    • Humans have little or no ability to conjure odor “images”
    • We do not think in smell, do not imagine smells
olfactory psychophysics identification and adaptation
Olfactory Psychophysics, Identification, and Adaptation
  • Detection, discrimination, and recognition
    • How much stimulation is required before we perceive something to be there?
    • Olfactory detection thresholds: Depend on several factors
olfactory psychophysics identification and adaptation1
Olfactory Psychophysics, Identification, and Adaptation
  • Women: Generally lower thresholds than men, especially during ovulatory period of menstrual cycles, but their sensitivity is not heightened during pregnancy
  • Professionals can distinguish up to 100,000 odors (e.g., professional perfumers, wine tasters)
  • Durability: Our recognition of smells is durable even after several days, month, or year
olfactory psychophysics identification and adaptation cont d
Olfactory Psychophysics, Identification, and Adaptation (cont’d)
  • Identification:
    • Attaching verbal label to smell is not easy
    • “Tip-of-the-nose phenomenon”
    • Compare to “tip-of-the-tongue” phenomenon
    • Anthropologists found that there are fewer words for experience of smells as opposed to other sensations
olfactory psychophysics identification and adaptation cont d1
Olfactory Psychophysics, Identification, and Adaptation (cont’d)
  • Sense of smell and language: Disconnected, possibly because:
      • Olfactory information is not integrated in thalamus prior to processing in cortex
      • Majority of olfactory processing occurs in right side of brain while language processing occurs in left side of brain
olfactory psychophysics identification and adaptation cont d2
Olfactory Psychophysics, Identification, and Adaptation (cont’d)
  • Adaptation:
    • Sense of smell is essentially a change detector
    • Examples: Walking into bakery, smelling strong perfume
    • Receptor adaptation
    • Cross adaptation
olfactory psychophysics identification and adaptation cont d3
Olfactory Psychophysics, Identification, and Adaptation (cont’d)
  • Cognitive habituation
    • After long-term exposure to an odorant, one is no longer able to detect that odorant or has very diminished detection ability
    • Example: Going out of town, coming back to house with smell
olfactory psychophysics identification and adaptation cont d4
Olfactory Psychophysics, Identification, and Adaptation (cont’d)
  • Three mechanisms involved in cognitive habituation:
      • Olfactory receptors internalized into cell bodies during odor adaptation may be hindered after continuous exposure, take longer to recycle
      • Odorant molecules may be absorbed into bloodstream causing adaptation to continue
      • Cognitive-emotional factors
olfactory psychophysics identification and adaptation cont d5
Olfactory Psychophysics, Identification, and Adaptation (cont’d)
  • The importance of attention
    • We cannot smell while we are asleep
    • Attention is cut off during sleep, therefore we cannot smell
olfactory hedonics
Olfactory Hedonics
  • Odor hedonics:
    • The liking dimension of odor perception; typically measured with scales pertaining to an odorant’s perceived pleasantness, familiarity, and intensity
olfactory hedonics cont d
Olfactory Hedonics (cont’d)
  • Familiarity and intensity:
    • We tend to like odors we’ve smelled many times before
    • Intensity: Interesting relationship to odor liking
olfactory hedonics cont d1
Olfactory Hedonics (cont’d)
  • Nature or nurture?
    • Are hedonic responses to odors innate or learned? Debate over this
    • Evidence from infants
    • Cross-cultural data supporting associative learning
    • An evolutionary argument
    • Learned taste aversions
olfactory hedonics cont d2
Olfactory Hedonics (cont’d)
  • Two caveats for theory that odor hedonics are mostly learned:
    • Trigeminally irritating odors may elicit pain responses, and all humans have innate drive to avoid pain
    • There is potential variability in receptor genes and pseudogenes that are expressed across individuals
olfaction memory and emotion
Olfaction, Memory, and Emotion
  • Are odors really the best cues to memory?
    • Other modalities can elicit memory as well (e.g., vision, touch, taste)
    • Memories triggered by odor cues are distinctive in their emotionality
    • Emotion and evocativeness of odor-elicited memories lead to false impression that such memories are especially accurate
olfaction memory and emotion cont d
Olfaction, Memory, and Emotion (cont’d)
  • Orbitofrontal cortex:
    • Olfaction is processed there
    • Also the cortical area for assigning affective value, (i.e., hedonic judgment)
objectives be able to1
Objectives: Be able to
  • Define olfactory receptor proteins, glomeruli, and odotopes.
  • Describe odorant transduction.
  • Relate olfactory receptor proteins, receptor neurons, glomeruli, and odotopes to odor identification.
  • Describe theories of olfaction.
  • Describe the major parts of any perfume and explain their functions.
  • Discuss memory for odors.