Sensory Processes

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Sensory Processes 3270 Lecture 6 (chemical
senses)
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KEYWORDS ---- VESTIBULAR I
CANALS rotation, cupula, hair cells coded by
looking at the difference between all three of
them example of a CHANNEL CODING
SYSTEM. OTOLITHS Translation, macula, hair
cells, utricle, saccule Coded by looking across
the activity of all fibres Example of a
POPULATION CODING SYSTEM.
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KEYWORDS ---- VESTIBULAR 2
eye movements (rotation), equal and opposite to
head movement, three pairs of eye muscles whose
direction of pull roughly corresponding to planes
of the canals, mathematical integration required
to change acceleration signal into a position
signal (must be done by the brain) eye movements
(translation), depend on (i) head movement (ii)
direction of target (eg. left or right) and (iii)
distance of target, geometry shown to be taken
into account by system eye movements (neural
pathway), hair cells gt afferent nerve (VIII) gt
vestibular nucleus gt oculomotor nuclei gt
oculomotor nerves (III, IV and VI) gt eye muscles
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Oculomotor III
Abducens VI
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The 12 Cranial Nerves
1 olfactory 2 optic 3 oculomotor 4 trochlear 5
trigeminal 6 abducens 7 facial 8 auditory and
vestibular 9 glossopharyngeal 10 vagus 11
accessory 12 hypoglossal
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III
III
Oculomotor nuclei (III)
Vestibular nerve (VIII)
VI
VI
Abducens nuclei (VI)
VN
VN
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KEYWORDS ---- VESTIBULAR 3
vestibulo-spinal reflexes, primitive
(evolutionarily), but capable of remarkable
complexity (organized response with many
muscles) multi-modal cues to self motion
vision and vestibular normally active together,
vestibular nucleus responds to EITHER vision OR
vestibular (or both), visual motion without
actual motion causes linear or circular vection
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KEYWORDS ---- VESTIBULAR 4
Self motion and ALCOHOL 1 alcohol -gt canals 2
alcohol rises and moves the fluid 3 causes head
to feel tilting DOWN 4 eyes move UP 5 retina past
still world -gt visual world moved DOWN 6 visual
vection created suggesting head tiltingUP 7 head
up and down at same time? 8 Must be poisoned. 9
GET RID OF IT!!!!
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KEYWORDS ---- VESTIBULAR 5
motion sickness (sensory conflict) reading in
vehicle, head movements in space, being below
deck in a ship SPACE navigation (path
integration) artificial gravity canals reacting
to heat in absence of gravity perception of
linear motion
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Sensory Processes 3270 Chemical senses TASTE
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Taste primaries sweet, sour, salty, bitter,
umani
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MAGNITUDE ESTIMATION

• Figure 15.14 The contribution of each of the four
  basic tastes to the tastes of KCl and NaNO3,
  determined by the method of magnitude estimation.
  The height of the line indicates the size of the
  magnitude estimate for each basic taste. (From
  McBurney, 1969.)

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1. Tongue
2. Papillae
3. Taste buds
4. Taste cells
5. Receptors

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THE TONGUE
Chorda tympani (part of facial VII)
Glossopharyngeal (IX)
Bitter Sour Salt Sweet
(Filiform have no taste buds)
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Fungiform
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Foleate
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Circumvallate
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TASTE BUDS
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TASTE BUDS
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• CODING in the TASTE SYSTEM
• Specificity (labelled lines)
• or
• Distributed code ???

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RESPONSES OF TASTE FIBRES TO DIFFERENT SALTS
sodium chloride
potassium chloride
ammonium chloride
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Now make potassium chloride aversive Rats avoid
BOTH potassium chloride AND ammonium
chloride But not sodium chloride Similar cell
patterns seem to correspond to similar
perceptions
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• Distributed
• cells respond to more than one primary
• across fibre patterns found
• Specificity
• cells broadly into 5 types
• salt
• sour
• bitter
• sweet
• umani
• . Each with different channel mechanisms
• salt deprived ? salt cells quiet

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RESPONSES OF TASTE FIBRES
salt type fibres
sweet type fibres
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Sweet Salt Sour Bitter

• SPECIFICITY CODING IN TASTE

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PTC tastes bitter to humans but not to mice. They
can be cloned to find the taste of PTC aversive.
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CONCLUSION Both distributed and specificity
(labelled line) codes are involved in determining
taste
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• taste thresholds
• depend on
• temperature (different primaries alter
  differently)
• Tongue region

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TASTE THRESHOLDS
salt
sweet
sour
THRESHOLDS
bitter
VARIATIONOVER TONGUE
VARIATION WITH TEMPERATURE
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• taste thresholds
• depend on
• temperature (different primaries alter
  differently)
• Tongue region
• genetics (phenylthiocarbamide to 2/3rds of white
  western folk tastes bitter 1/3rd no
  taste)
• concentration (eg. saccharin low sweet high
  bitter)
• Age
• adaptation

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taste preferences, Humans sweet
() bitter (-) (mostly in place at
birth) Cats /chickens indifferent to
sweet rat/cat/rabbit/sheep salt ()
hamster salt (-) taste
cravings, salt, calcium, potassium, etc..
specific changes in threshold when deprived (eg.
for salt) cultural influences, conditioned
taste aversion
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TASTE PATHWAY

• neural pathway (uncrossed)
• taste cells,
• VII cranial nerves (corda tympani division of
  facial nerve), IX cranial nerve
  (glossopharyngeal),
• solitary nucleus
• ventral posterior medial nucleus of thalamus,
• taste cortex (near mouth representation of
  somatosensory cortex)

4. to cortex
3. to thalamus
VII
IX
1. receptors
2. nerves
also brain stem vomit centres
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Taste cortex
Central sulcus
TASTE AREA I
TASTE AREA II
Ventro-posterior medial thalamus