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

Psychology 355 3

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+

Psychology 355 4

Advantage ± Survival: Poisonoussubstances - often bitter

Single-Trial Learning; Self-Balancing Diet

Psychology 355 5

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

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

Psychology 355 7

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

Psychology 355 8

The Organs of Taste

Tongue, mouth, palate, pharynx, andepiglottis

Psychology 355 9

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

Psychology 355 10

The Organs of Tastes

A. Papillae

1. Foliate papillae

2. Vallate papillae3. Fungiform papillae

Threshold concentrationJust enough exposure of single

papilla to detect taste

Psychology 355 11

I. TastesReceptor Cells

A. Apicalends

MicrovilliTaste pore

B. Receptorpotential:Voltageshift

Psychology 355 12

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)

Psychology 355 13

Mechanisms of TasteTransduction

Saltiness

1. Salt-sensitive tastecells

i. Special Na+

selective

channel2. Blocked by the

drug amiloride

Psychology 355 14

Sourness

1. Sourness-acidity ± low pH

2. Protons

causative agentsof acidity andsourness

Psychology 355 15

Bitter, Sweet, UmamiA. G-protein coupled

receptorB. Activates

Phospholipase CC. Increases messenger

inositol triphosphate(IP3)

D. CA2+

Psychology 355 16

Bitterness

1. Families of taste receptorgenes - TIR

and T2R

Psychology 355 17

Mechanisms of Taste Transduction

Sweetness

1. Sweet tastants natural and

artificial

2. Sweet receptors

i. T1R2+T1R3

ii. Expressed in different tastecells

Psychology 355 18

A. Umami

1. Umamireceptors:

i. Detect

amino acidsii. T1R1+T1R3

Psychology 355 19

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

Psychology 355 20

Psychology 355 21

Psychology 355 22

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

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

Pheromones

A. Smell² a mode of communication

B. Important signals

1. Reproductive behavior2. Territorial boundaries

3. Identification

4. AggressionC. Role of human pheromones

Psychology 355 25

The Organs of Smell

Olfactory epithelium

Olfactory receptor cells, supporting

cells, and basal cells

Psychology 355 26

Psychology 355 27

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

Psychology 355 28

Perception of Smell

The dimensions of smell

FloweryFoul

Fruity

Resinous

Psychology 355 29

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

Psychology 355 30

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

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)

Psychology 355 33

Pheromones: Mammals I. Releasers

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

increases the likelihood of certain types of behaviors

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

Olfactory Receptor Neurons

A. Olfactory Transduction

Psychology 355 37

Olfactory Receptor Neurons

Olfactory Transduction

Oderant to receptor protein

Stimulates G(olf)-proteinActivates adenylyl cyclase

Opens Na+ Ca2+ channels

Opens Cl- channels (out)

Depolarization

Psychology 355 38

Olfactory

Receptor

Neurons

Olfactory

Transduction

Psychology 355 39

Olfactory Transduction

Adaptation:Decreased response

despite continuousstimulus

Psychology 355 40

Central Olfactory

Pathways

Olfactory Bulb

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

Limbic and

Thalamic

connections

Olfactory cortex(frontal

Psychology 355 42

Central Olfactory Pathways

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

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

Psychology 355 45

I. Spatial and TemporalRepresentations of OlfactoryInformation

A. Olfactory Population Coding

B. Olfactory Maps (sensorymaps)

C. Temporal Coding in theOlfactory System

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

End of Presentation

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