Download 04 Chemical Senses

04 The Chemical Senses
Psychology 355
Introduction
I.
Animals depend on the chemical senses to
identify nourishment
II. Chemical sensation
A. Oldest and most common sensory
system
III. Chemical senses
A. Gustation
B. Olfaction
C. Chemoreceptors
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Taste
The Basics Tastes
1.
Saltiness
2.
sourness,
3.
sweetness,
4.
bitterness, and
5.
Umami
Examples of correspondence between chemistry
1.
Sweet—sugars like fructose, sucrose, artificial
sweeteners (saccharin and aspartame)
2.
Bitter—ions like K+ and Mg2+, quinine, and
caffeine
3.
Sour— Acidity (low Ph), H+
4.
Salt—Na+
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Taste
Advantage – Survival: Poisonous
substances - often bitter
Single-Trial Learning; Self-Balancing Diet
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Taste
The Basics Tastes
1.
Saltiness
2.
sourness,
3.
sweetness,
4.
bitterness, and
5.
Umami
chemistry
1.
Sweet—sugars like fructose,
sucrose, artificial
sweeteners (saccharin and
aspartame)
2.
Bitter—ions like K+ and
Mg2+, quinine, and caffeine
3.
Sour— Acidity (low Ph), H+
4.
Salt—Na+
Advantage – Survival: Poisonous
substances - often bitter
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Taste
The Basics Tastes
A.
Saltiness
B.
sourness,
C.
sweetness,
D.
bitterness, and
E.
Umami
chemistry
A.
Sweet—sugars like
fructose, sucrose,
artificial sweeteners
(saccharin and
aspartame)
B.
Bitter—ions like K+ and
Mg2+, quinine, and
caffeine
C.
Sour— Acidity (low Ph),
H+
D.
Salt—Na+
Advantage – Survival: Poisonous
substances - often bitter
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Taste
The Basic Tastes
A. Steps to distinguish the countless
unique flavors of a food
1. Each food activates a different
combination of taste receptors
2. Distinctive smell
3. Other sensory modalities
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Taste
The Organs of Taste
Tongue, mouth, palate, pharynx, and
epiglottis
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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 papillae
3. Fungiform papillae
Threshold concentration
Just enough exposure of single
papilla to detect taste
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Taste
I.
Tastes
Receptor Cells
A.
Apical
ends
Microvilli
Taste pore
B.
Receptor
potential:
Voltage
shift
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Taste
Mechanisms of Taste Transduction
A. Transduction process
1. Taste stimuli (tastants)
i. Pass directly through ion
channels (Na+)
ii. Bind to and block ion channels
(sour-H+)
iii. Bind to G-protein-coupled
receptors (bitter, sweet,
umami)
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Taste
Mechanisms of Taste
Transduction
Saltiness
1. Salt-sensitive taste
cells
i.
Special Na+
selective
channel
2. Blocked by the
drug amiloride
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Taste
Mechanisms of Taste
Transduction
Sourness
1. Sournessacidity – low pH
2. Protons
causative agents
of acidity and
sourness
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Taste
Mechanisms of Taste
Transduction
Bitter, Sweet, Umami
A. G-protein coupled
receptor
B. Activates
Phospholipase C
C. Increases messenger
inositol triphosphate
(IP3)
D. CA2+
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Taste
Mechanisms of Taste
Transduction
Bitterness
1. Families of
taste receptor
genes - 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 taste
cells
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Taste
Mechanisms of Taste
Transduction
A. Umami
1. Umami
receptors:
i. Detect
amino acids
ii. T1R1+T1R3
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Taste
Central Taste Pathways
A. Gustatory nucleus
Point where taste axons bundle and
synapse
B. Ventral posterior medial nucleus
(VPM) of the thalamus
C. Primary gustatory cortex
Receives axons from VPM taste
neurons
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Taste
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Taste
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Taste
Central Taste Pathways (Cont’d)
A. Localized lesions
1. Ageusia- the loss of taste perception
B. Gustation
1.
Important to the control of feeding
and digestion
i.
Hypothalamus
ii. Basal telencephalon
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Taste
The Neural Coding of Taste
A. Labeled line hypothesis
1. Individual taste receptor cells for
each stimuli
2. In reality, neurons broadly tuned
3. Population coding
i.
Roughly labeled lines
ii. Temperature
iii. Textural features of food
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Smell
Pheromones
A. Smell— a mode of communication
B. Important signals
1. Reproductive behavior
2. Territorial boundaries
3. Identification
4. Aggression
C. Role of human pheromones
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Smell
The Organs of Smell
Olfactory epithelium
Olfactory receptor cells, supporting
cells, and basal cells
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Smell
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Smell
The Organs of Smell
A.
Odorants: Activate transduction processes in
neurons
B.
Olfactory axons constitute olfactory nerve
C.
Cribriform plate: A thin sheet of bone through
which small clusters of axons penetrate,
coursing to the olfactory bulb
D.
Anosmia: Inability to smell
E.
Humans: Weak smellers
Due to small surface area of olfactory epithelium:
Dogs have about 170 cm2 compared to 10
cm2 in humans, and about 100 times more
receptors per unit area
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Perception of Smell
The dimensions of smell
Foul
Flowery
Fruity
Burnt
Resinous
Spicy
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Perception of Smell (cont.)
I.
II.
We can distinguish between about 10,000 different
smells
Different threshold levels for different smells
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.
II.
Adaptation - Olfactory fatigue - cross-adaptation
Smell Constancy - receptors are more stimulated
during a deep sniff than a shallow one - the judgment
of odor intensity does not change -
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Smell
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Pheromones: Mammals
Powerful effects on behavior, specifically
sexual behavior, territorial behavior and
identification of kin
Mammals
I.
Most mammals only become sexually aroused
in the presence of pheromones
II. Increased likelihood of pregnancy
III. Synchronization of estrus cycles
IV. Mutual recognition of mother and offspring
V. Territory marking (e.g. dogs)
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Pheromones: Mammals
I.
II.
Releasers - trigger a specific behavioral response
Primers - trigger a hormone response which
increases the likelihood of certain types of behaviors
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Pheromones: Humans
Humans
I.
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
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territorial marker among males
Pheromones: Humans
Increase 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 androstenol
II. 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
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Smell
Olfactory Receptor Neurons
A. Olfactory Transduction
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Smell
Olfactory Receptor Neurons
Olfactory Transduction
Oderant to receptor protein
Stimulates G -protein
Activates adenylyl cyclase
cAMP
Opens Na+ Ca2+ channels
Opens Cl- channels (out)
Depolarization
(olf)
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Smell
Olfactory
Receptor
Neurons
Olfactory
Transduction
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Smell
Olfactory Transduction
Adaptation:
Decreased response
despite continuous
stimulus
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Smell
Central Olfactory
Pathways
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Olfactory Bulb
Olfactory bulb - organ which houses all the nerves which receive inputs from
the olfactory receptors
Limbic and
Thalamic
connections
Olfactory cortex
(frontal
lobe)
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Smell
Central Olfactory Pathways
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Smell
Central Olfactory Pathways
A. Axons of the olfactory tract: Branch and
enter the forebrain
B. Neocortex: Reached by a pathway that
synapses in the medial dorsal nucleus
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Smell
Central Olfactory Pathways
A.
Axons of the olfactory tract: Branch and enter the
forebrain
B.
Neocortex: Reached by a pathway that synapses in the
medial dorsal nucleus
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Smell
I.
Spatial and Temporal
Representations of Olfactory
Information
A. Olfactory Population Coding
B. Olfactory Maps (sensory
maps)
C. Temporal Coding in the
Olfactory System
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Concluding Remarks
I.
Transduction mechanisms
A.
Gustation and olfaction
II. Similar to the signaling systems used
in every cell of the body
III. Common sensory principles - broadly
tuned cells
A. Population coding
B. Sensory maps in brain
IV. Timing of action potentials
A. May represent sensory information
in ways not yet understood
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End of Presentation
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