Sensory Processes 3270 Lecture 6 (chemical senses)
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Transcript of Sensory Processes 3270 Lecture 6 (chemical senses)
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Sensory Processes3270
Lecture 6
(chemical senses)
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KEYWORDS ---- VESTIBULAR I
CANALS
rotation, cupula, hair cellscoded by looking at the difference between all
three of them example of a CHANNEL CODING SYSTEM.
OTOLITHS
Translation, macula, hair cells, utricle, sacculeCoded by looking across the activity of all fibresExample 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 > afferent nerve (VIII) > vestibular nucleus > oculomotor nuclei > oculomotor nerves (III, IV and VI) > eye muscles
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AbducensVI
OculomotorIII
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The 12 Cranial Nerves
1 olfactory2 optic3 oculomotor4 trochlear5 trigeminal6 abducens7 facial8 auditory and vestibular9 glossopharyngeal10 vagus11 accessory12 hypoglossal
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VN VN
VI VI
IIIIII Oculomotor nuclei (III)
Abducens nuclei (VI)Vestibular nerve (VIII)
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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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Self motion and ALCOHOL
1 alcohol -> canals2 alcohol rises and moves the fluid3 causes head to feel tilting DOWN4 eyes move UP5 retina past still world -> visual world moved DOWN6 visual vection created suggesting head tiltingUP7 head up and down at same time?8 Must be poisoned.9 GET RID OF IT!!!!
KEYWORDS ---- VESTIBULAR 4
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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 Processes3270
Chemical sensesTASTE
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Taste primaries: sweet, sour, salty, bitter, umani
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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.)
MA
GN
ITU
DE
ES
TIM
AT
ION
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1. Tongue2. Papillae3. Taste buds4. Taste cells5. Receptors
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THE TONGUE
(Filiform have no taste buds)
Glossopharyngeal (IX)
Chorda tympani (part of facial VII)
Bitter
Sour
Salt
Sweet
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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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ammonium chloride
sodium chloride
potassium chloride
RESPONSES OF TASTE FIBRES TO DIFFERENT SALTS
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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
saltsourbittersweetumani
• …. Each with different channel mechanisms• salt deprived salt cells quiet
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salt type fibressweet type fibres
RESPONSES OF TASTE FIBRES
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SPECIFICITY CODING IN TASTE
Sweet
Salt
Sour
Bitter
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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:
1. temperature (different primaries alter differently)
2. Tongue region
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VARIATION WITH TEMPERATURE
VARIATIONOVER TONGUE
TASTE THRESHOLDSsalt
sweet
sour
bitter
TH
RE
SH
OL
DS
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taste thresholds
depend on:
1. temperature (different primaries alter differently)
2. Tongue region
3. genetics (phenylthiocarbamide: to 2/3rds of white western folk tastes bitter; 1/3rd no taste)
4. concentration (eg. saccharin low sweet; high bitter)
5. Age
6. 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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neural pathway (uncrossed)
1 taste cells, 2 VII cranial nerves
(corda tympani division of facial nerve), IX cranial nerve (glossopharyngeal),
3 solitary nucleus4 ventral posterior
medial nucleus of thalamus,
5 taste cortex (near mouth representation of somatosensory cortex)
also brain stem vomit centres
1. receptors2. nerves
VII
IX
3. to thalamus
4. to cortex
TASTE PATHWAY
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Ventro-posterior
medial thalamus
Taste cortex
Central sulcus
TASTE AREA I
TASTE AREA II