04 chemical senses

8/6/2019 04 Chemical Senses

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Psychology 355

04 The Chemical Senses



Psychology 355 2

Introduction

I. Animals depend on the chemical senses toidentify nourishment

II. Chemical sensation

A. Oldest and most common sensorysystem

III. Chemical senses

A. Gustation

B. Olfaction

C. Chemoreceptors



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Taste

The Basics Tastes1. Saltiness

2. sourness,

3. sweetness,

4. bitterness, and5. Umami

Examples of correspondence between chemistry

1. Sweet²sugars like fructose, sucrose, artificial

sweeteners (saccharin and aspartame)2. Bitter²ions like K+ and Mg2+, quinine, andcaffeine

3. Sour² Acidity (low Ph), H+

4. Salt²Na+



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Taste

Advantage ± Survival: Poisonoussubstances - often bitter

Single-Trial Learning; Self-Balancing Diet



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Taste

The Basics Tastes1. Saltiness2. sourness,3. sweetness,4. bitterness, and5. Umami

chemistry1. Sweet²sugars like fructose,

sucrose, artificialsweeteners (saccharin andaspartame)

2. Bitter²ions like K+ andMg2+, quinine, and caffeine

3. Sour² Acidity (low Ph), H+4. Salt²Na+

Advantage ± Survival: Poisonoussubstances - often bitter



Psychology 355 6

Taste

The Basics TastesA. SaltinessB. sourness,C. sweetness,D. bitterness, andE. Umami

chemistry

A. Sweet²sugars likefructose, sucrose,artificial sweeteners(saccharin andaspartame)

B. Bitter²ions like K+ andMg2+, quinine, andcaffeine

C. Sour² Acidity (low Ph),H+

D. Salt²Na+Advantage ± Survival: Poisonous

substances - often bitter



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Taste

The Basic Tastes

A. Steps to distinguish the countlessunique flavors of a food

1. Each food activates a differentcombination of taste receptors

2. Distinctive smell

3. Other sensory modalities



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Taste

The Organs of Taste

Tongue, mouth, palate, pharynx, andepiglottis



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Taste

Areas of sensitivity on the tongue

1. Tip of the tongue

Sweetness

2. Back of the tongue

Bitterness

3. Sides of tongues

Saltiness and sourness



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Taste

The Organs of Tastes

A. Papillae

1. Foliate papillae

2. Vallate papillae3. Fungiform papillae

Threshold concentrationJust enough exposure of single

papilla to detect taste



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Taste

I. TastesReceptor Cells

A. Apicalends

MicrovilliTaste pore

B. Receptorpotential:Voltageshift



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Taste

Mechanisms of Taste TransductionA. Transduction process

1. Taste stimuli (tastants)

i. Pass directly through ionchannels (Na+)

ii. Bind to and block ion channels

(sour-H+)iii. Bind to G-protein-coupledreceptors (bitter, sweet,umami)



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Taste

Mechanisms of TasteTransduction

Saltiness

1. Salt-sensitive tastecells

i. Special Na+

selective

channel2. Blocked by the

drug amiloride



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Taste


Sourness

1. Sourness-acidity ± low pH

2. Protons

causative agentsof acidity andsourness



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Taste


Bitter, Sweet, UmamiA. G-protein coupled

receptorB. Activates

Phospholipase CC. Increases messenger

inositol triphosphate(IP3)

D. CA2+



Psychology 355 16

Taste


Bitterness

1. Families of taste receptorgenes - TIR

and T2R



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Taste

Mechanisms of Taste Transduction

Sweetness

1. Sweet tastants natural and

artificial

2. Sweet receptors

i. T1R2+T1R3

ii. Expressed in different tastecells



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Taste


A. Umami

1. Umamireceptors:

i. Detect

amino acidsii. T1R1+T1R3



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Taste

Central Taste PathwaysA. Gustatory nucleus

Point where taste axons bundle and

synapseB. Ventral posterior medial nucleus

(VPM) of the thalamus

C. Primary gustatory cortex

Receives axons from VPM tasteneurons



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Taste



Psychology 355 21

Taste



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Taste

Central Taste Pathways (Cont¶d)

A. Localized lesions

1. Ageusia- the loss of taste perception

B. Gustation1. Important to the control of feeding

and digestion

i. Hypothalamus

ii. Basal telencephalon



Psychology 355 23

Taste

The Neural Coding of Taste

A. Labeled line hypothesis

1. Individual taste receptor cells for

each stimuli2. In reality, neurons broadly tuned

3. Population coding

i. Roughly labeled lines

ii. Temperature

iii. Textural features of food



Psychology 355 24

Smell

Pheromones

A. Smell² a mode of communication

B. Important signals

1. Reproductive behavior2. Territorial boundaries

3. Identification

4. AggressionC. Role of human pheromones



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Smell

The Organs of Smell

Olfactory epithelium

Olfactory receptor cells, supporting

cells, and basal cells



Psychology 355 26

Smell



Psychology 355 27

Smell

The Organs of SmellA. Odorants: Activate transduction processes in

neuronsB. Olfactory axons constitute olfactory nerveC. Cribriform plate: A thin sheet of bone through

which small clusters of axons penetrate,coursing to the olfactory bulb

D. Anosmia: Inability to smellE. Humans: Weak smellers

Due to small surface area of olfactory epithelium:

Dogs have about 170 cm2 compared to 10cm2 in humans, and about 100 times morereceptors per unit area



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Perception of Smell

The dimensions of smell

FloweryFoul

Fruity

Spicy

Burnt

Resinous



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Perception of Smell (cont.)

I. We can distinguish between about 10,000 differentsmells

Different threshold levels for different smells

II. Two thresholds for each smell -low threshold for the

existence of a chemical, somewhat higher threshold to

discriminate one smell from another



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Perception of Smell

I. Adaptation - Olfactory fatigue - cross-adaptation

II. Smell Constancy - receptors are more stimulated

during a deep sniff than a shallow one - the judgment

of odor intensity does not change -



Psychology 355 31

Smell



32

Pheromones: Mammals

Powerful effects on behavior, specifically

sexual behavior, territorial behavior and

identification of kin

MammalsI. Most mammals only become sexually aroused

in the presence of pheromones

II. Increased likelihood of pregnancyIII. Synchronization of estrus cycles

IV. Mutual recognition of mother and offspring

V. Territory marking (e.g. dogs)



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Pheromones: Mammals I. Releasers

- trigger a specific behavioral response II. Primers- trigger a hormone response which

increases the likelihood of certain types of behaviors



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Pheromones: Humans

HumansI. infants can correctly identify their own

mother's milk and are much more likely to

nurse when its their own mother

II. female menstrual cycles can be altered by

pheromones - the sorority effect

III. male and female behavior is highly influenced

by pheromones

t-shirt experiment - musky versus sweet -

IV. the musky odor is rated by males and females

as unpleasant and is thought to serve as a

territorial marker among males



Psychology 355 35

Pheromones: HumansIncrease sexual arousal in males

I. Increases male perception of female attractiveness

� women in photographs were rated as significantly more

sexually attractive when judges were first exposed to

alpha androstenolII. 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



Psychology 355 36

Smell

Olfactory Receptor Neurons

A. Olfactory Transduction



Psychology 355 37

Smell

Olfactory Receptor Neurons

Olfactory Transduction

Oderant to receptor protein

Stimulates G(olf)-proteinActivates adenylyl cyclase

cAMP

Opens Na+ Ca2+ channels

Opens Cl- channels (out)

Depolarization



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Smell

Olfactory

Receptor

Neurons

Olfactory

Transduction



Psychology 355 39

Olfactory Transduction

Adaptation:Decreased response

despite continuousstimulus

Smell



Psychology 355 40

Central Olfactory

Pathways

Smell



41

Olfactory Bulb

Olfactory bulb - organ which houses all the nerves which receive inputs fromthe olfactory receptors

Limbic and

Thalamic

connections

Olfactory cortex(frontal

lobe)



Psychology 355 42

Central Olfactory Pathways

Smell



Psychology 355 43

Central Olfactory Pathways

A. Axons of the olfactory tract: Branch andenter the forebrain

B. Neocortex: Reached by a pathway thatsynapses in the medial dorsal nucleus

Smell



Psychology 355 44

Central Olfactory PathwaysA. Axons of the olfactory tract: Branch and enter the

forebrain

B. Neocortex: Reached by a pathway that synapses in themedial dorsal nucleus

Smell



Psychology 355 45

I. Spatial and TemporalRepresentations of OlfactoryInformation

A. Olfactory Population Coding

B. Olfactory Maps (sensorymaps)

C. Temporal Coding in theOlfactory System

Smell



Psychology 355 46

Concluding Remarks

I. Transduction mechanisms

A. Gustation and olfaction

II. Similar to the signaling systems used

in every cell of the bodyIII. Common sensory principles - broadlytuned cells

A. Population coding

B. Sensory maps in brainIV. Timing of action potentials

A. May represent sensory informationin ways not yet understood



Psychology 355

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04 chemical senses

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