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Sensation and Perception > Chapter 14: Olfaction: Perceiving Odors > Flashcards

Chapter 14: Olfaction: Perceiving Odors Flashcards

1
Q

Perceiving Odors: Olfaction

A
  • Olfaction tends to be vastly under appreciated by most people
  • Like other senses, olfaction is subject to adaptation
  • Recent genetic research findings and subsequent techniques in molecular biology and cellular imaging advance the discovery of a neural code for smell
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2
Q

What is an odor?

A

The olfactory system detects molecules of odorant if they are sufficiently concentrated to stimulate receptors

  • olfaction is an analytic sense
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3
Q

What is an odorant?

A

Molecules that olfactory receptors “recognize” and respond to by respond to by producing neural signals that the brain represents as perceptions of different odors

  • molecule must be present at great enough concentrations to evoke a response
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4
Q

What is a molecule?

A
  • Two or more atoms bound together by electromagnetic forces

- Number of atoms in a molecule can vary widely

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5
Q

For humans, most odorants are made from only five atoms

A 
Carbon
Hydrogen
Oxygen
Nitrogen
Sulfur
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6
Q

Odorant molecules with similar molecular structures can smell very […] and odorants with very different structures can smell almost […]

A

Odorant molecules with similar molecular structures can smell very different and odorants with very different structures can smell almost the same

  • determined by ppm analysis
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7
Q

Thresholds

A

Detection threshold
Absolute threshold
Difference thresholds

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8
Q

Detection thresholds

A

Concentrations of odorant necessary for person to detect it

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9
Q

Crucial factor in detecting odor is […]

A

Crucial factor in detecting odor is concentration of odorant molecules

  • concentration depends on what the source is, how far away it is, and whether molecules are confined to small space
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10
Q

Absolute Detection Threshold: Vanillin

A

Flavoring extracted from vanilla bean

0.000035 ppm

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11
Q

Absolute Detection Threshold: t-butyl mercaptan

A

Added to natural gas to aid in detection of leaks

0.00033 ppm

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12
Q

Absolute Detection Threshold: hydrogen sulfide

A

Colorless, poisonous, flammable gas

0.017 ppm

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13
Q

Absolute Detection Threshold: Menthol

A

Active ingredients in various medicinal compounds

0.04 ppm

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14
Q

Absolute Detection Threshold: camphor

A

Active ingredient in various medicinal compounds

0.05 ppm

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15
Q

Absolute Detection Threshold: chlorine

A

Disinfectant

0.5 ppm

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16
Q

Absolute Detection Threshold: Formaldehyde

A

Disinfectant and embalming agent

0.87 ppm

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17
Q

Absolute Detection Threshold: Isopropyl alcohol

A

Solvent and cleaning fluid

10 ppm

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18
Q

Absolute Detection Threshold: acetone

A

Nail polish remover

15 ppm

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19
Q

Absolute Detection Threshold: methanol

A

Antifreeze and solvent

141 ppm

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20
Q

Identifying and discriminating odors

A
  • Source, distance, area, and context affect the concentration of odors
  • Training and experience affect detection
  • Age, smoking, certain diseases and genetic mutations, and injury lead to reduced olfactory performance
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21
Q

Odors play a key role in […]

A

Odors play a key role in sensing flavors

  • about 96% people with taste deficit have olfactory deficit
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22
Q

Anosmia

A

Loss of ability to perceive odors (less than 18)

*Congentical anosmia- deformed/ absent olfactory bulbs

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23
Q

Smell is an early warning system

A

Adaptation to odors

    - Responsiveness to change
    - Adaption to constant stimulation
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24
Q

Cross- Adaptation

A

In olfaction, reduced sensitivity to odorant that are chemically or perceptually similar to odorants to which persons has been continuously or repeatedly exposed

  • molecular similarity does not always predict cross-adaptation
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25
Q

Pathway of Olfactory Information

A
  1. Approximately 1,000 genes expressing GPCRs were discovered by Buck and Axel; these genes represent roughly 4% of the human genome
  2. The olfactory nerve, composed of axons from ORNs, passes into the brain by way of the cribiform plate, stopping first at the mitral and tufted relay neurons of the glomeruli
  3. Once past the glomeruli the axons are now called the olfactory tract
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26
Q

Turbinates

A

Body convolutions of tissue protruding into nasal cavities, functioning to disperse air evenly throughout nasal cavities

27
Q

Olfactory Epithelium

A

Patch of tissue in upper reaches of each nasal cavity

  • contains ORNs and is covered by layer of olfactory mucus
28
Q

Olfactory Receptor Neurons (ORNs)

A

Neurons that transduce odorant molecules into neuron signals

  • found in olfactory epithelium
  • each ORN has cilia that projects into mucus layer
  • each ORN dies after few weeks and replaced
  • basal cells are precursors of new ORNs
  • Bowman’s glands continually secrete mucus (which covers olfactory epithelium)
  • Mucus flows toward back of nasal cavity and into pharynx and then is swallowed
29
Q

Pathway of Olfactory Information (stimuli)

A
  1. While there are very few types of receptors for vision and hearing, there are approximately 350 different types of receptors for olfaction
  2. Because there are so many, each is sensitive to only one type of stimulus
  3. All together there are 3-7 million ORNs (10- 20,000 of each of the roughly 350 types) sending their signals to approximately 5,000 glomeruli
30
Q

Olfactory system: from nose to brain

A

Transduction of odorant molecules into neural signals are carried out by ORNs in the olfactory epithelium

  • olfactory epithelium
31
Q

Olfactory Receptors

A

GPCRs in cilia of ORNs

32
Q

G-protein couple receptors

A

Large family of proteins that function as receptors

  • provide a mechanism for molecules outside a cell to influence the inner working of cell
33
Q

Olfactory Nerve

A

Axons of ORNs, carrying neural signals from ORNs to olfactory build via tiny holes in cribiform plate

34
Q

Cribiform plate

A

Part of skull immediately above nasal cavity

  • axons of ORNs pass through grid of tiny holes in plate
35
Q

Mitral cell

A

Relay neurons within glomeruli in olfactory bulb

36
Q

Tufted cell

A

Relay neurons within glomeruli in olfactory bulb

37
Q

Glomerulus

A

Small, more or less spherical structures in olfactory bulb

  • within glomeruli, axons of ORNs make synapses with dendrites of mitral cells and tufted cells
38
Q

Olfactory tract

A

Axons of mitral and tufted cells

  • carry neural signals from olfactory areas of brain
39
Q

Olfaction uses […] code

A

Olfaction uses population code

  • Olfactory system identifies stimuli by looking at the pattern of responding of a group of ORNs (population coding); relatively narrowly tuned
  • This allows the olfactory system to distinguish many different smells from other odors
40
Q

Molecular Basis of Population Codes for Odors

A
  1. Eight different types of odorants molecules are distinguished by combinations of chemical features (colored shapes) that can bind to (fit into) the receptors (indentations) on four different types of ORNs
  2. Molecule 8 can bind to three of the other four ORN types, Molecules 7 can bind to only one ORN type, and all others can bind to two ORN types, but no two molecules bind to the same subset of ORNs
  3. In this model on the next slide, there are only eight molecules, with from one to three chemical features each, and just four types of ORNs
  4. In reality, there are about 350 types of ORNs, and there are thousands of odorant molecules with a very large number of feature combinations
41
Q

Molecular Basis of Population Codes for Odors: ORNs

A
  • Any given odorant molecules evoked response from some ORNs but not to others
  • Any ORN might respond strongly to some odorant molecules, weakly to other, and not at all to some others
42
Q

Chemotopic mapping

A

Axons of ORNs activated by odorants with similar molecular structures tend to travel to glomeruli in same part of olfactory bulb and, conversely, glomeruli in different parts of bulb tend to receive axons of ORNs activated by odorants with different molecular structures

43
Q

Representing odors in the brain

A

Odors leave the olfactory bulb and travel to three areas

  • Piriform cortex
  • Amygdala
  • Entorhinal cortex
44
Q

Piriform Cortex

A

Brain region considered to be primary olfactory cortex, because it’s only region that receives signals directly from olfactory bulb and is known to be dedicated solely to olfaction

45
Q

Amygdala

A

Activated by emotional stimuli and goes to hypothalamus

46
Q

Entorhinal cortex

A

Gateway to hippocampus where there is long-term memories

47
Q

Signals from amygdala, Piriform cortex, and Entorhinal cortex goes to […]

A

Orbitofrontal cortex: plays role in evaluating stimuli as positive and negative

48
Q

Separate cortical representations of odor identity and pleasantness

A

The Piriform cortex is composed of two sections

  • Anterior Piriform Cortex (APC)
  • Posterior Piriform Cortex (PPC)
49
Q

Anterior Piriform Cortex (APC)

A

It produces representations of features of chemical structure of odorant molecules

50
Q

Posterior Piriform Cortex (PPC)

A

Produces representations of quality of odor as whole, regardless of whether odor is simple or complex

51
Q

Anatomical and Neural Basis of Odor Perception: Stettler and Axel

A
  • Olfactory epithelium of mice exposed to different odorants and response to populations of Piriform cortex neurons was recorded
  • Each odorant evoked a highly consistent pattern of activity in Piriform cortex neurons but no consistent clustering appeared/ no apparent chemotopic organization
52
Q

Identity and pleasantness of odors

A
  • People are very good at determining whether they find an odor positive or negative despite the fact they might nit be able to identify it
  • Classifying odors as positive or negative is at least partially learned behavior
53
Q

Odors and Emotions

A

Humans are very good at consistently assessing an odor as pleasant or unpleasant

  • Some odors are dependent on state of the smeller
  • Other seemed to always be experienced as the same
  • Disgust reaction may be developmental or evolutionary in nature
  • Reinforced by amygdala and OFC
54
Q

Odors and Memory

A
  • Memories for odors are rapidly formed, long-lasting, and excellent triggers for emotions
  • Recall of odors shows a recency effort
  • The strong link to memory is assumed to be due to olfaction’s early evolutionary development and more direct links to areas like the hypothalamus and the hippocampus
55
Q

Recency Effort

A

Percentage of memories is higher for most recent decade than earlier decade

56
Q

Pheromones, Sweat, and Tears

A
  • Importance of human pheromones in social and reproductive functions remain controversial
  • Some research suggest substances emitted by humans can affect the behavior of other humans
  • However sexual behavior in humans is undoubtedly due to many other factors
57
Q

Do humans emit substances that have positive effects on sexual thoughts, moods, or behaviors of others?

A
  • Love potions
  • Estratetraneol
  • Androstradienone
58
Q

Estratetraneol

A

Steroid derived from hormone produced by women

59
Q

Androstriadienone

A

Steroid derived from hormones produced by men

60
Q

Vomeronasal Olfactory System

A

In many species, an olfactory system that senses pheromones

  • it is distinct from main olfactory system used to smell most substance
61
Q

Female Brain responses to male odors using fMRI

A

Only sexual sweat caused a significant increase over baseline, after just few seconds

Smell response tend to be stronger on the right side of brain

62
Q

Male and Female Pheromones

A
  • Substances emitted by individuals of one sex and sensed via the olfactory system by individuals of the other sex can evoke changes in sex-related mood, levels of arousal, approach behaviors, and hormone levels
  • Human sexual behavior is complex and multifaceted and is dependent on a variety of cognitive and social factors, as well as on physiological factors such as hormone and pheromones
  • Human pheromones, if they exist, are more likely to have subtle shaping effects on sexual behavior than to directly cause specific behaviors
63
Q

Human Leukocyte Antigen Detection

A

Can olfactory detection of certain genes influence human mating behavior?

  • An effective immune system enhances human survival
  • Human leukocyte antigens (HLAs) are the genes responsible for regulating the immune system
  • Children of parents with dissimilar HLAs tend to have more protective immune systems
64
Q

Human Leukocyte Antigen

A

The genes responsible for regulating the immune system

  • women can detect HLA difference in odors from men, possibly influencing their selection of a mate

Sensation and Perception (14 decks)

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