Sensory Processes
3270
Lecture 6
(chemical senses)
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.
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
Abducens
VI
Oculomotor
III
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
III
Oculomotor nuclei (III)
III
Vestibular nerve (VIII)
VI
VN
VI
VN
Abducens nuclei (VI)
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
KEYWORDS ---- VESTIBULAR 4
Self motion and ALCOHOL
1 alcohol -> canals
2 alcohol rises and moves the fluid
3 causes head to feel tilting DOWN
4 eyes move UP
5 retina past still world -> 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!!!!
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
Sensory Processes
3270
Chemical senses
TASTE
Taste primaries: sweet, sour, salty, bitter, umani
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.)
1.
2.
3.
4.
5.
Tongue
Papillae
Taste buds
Taste cells
Receptors
THE TONGUE
Chorda tympani
(part of facial VII)
Glossopharyngeal
(IX)
Bitter
Sour
Salt
Sweet
(Filiform have no taste buds)
Fungiform
Foleate
Circumvallate
TASTE BUDS
TASTE BUDS
CODING in the TASTE SYSTEM
•Specificity (labelled lines)
or
•Distributed code ???
RESPONSES OF TASTE FIBRES TO DIFFERENT SALTS
sodium chloride
potassium chloride
ammonium chloride
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”
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
RESPONSES OF TASTE FIBRES
salt type fibres
sweet type fibres
Sweet
Salt
Sour
Bitter
SPECIFICITY CODING IN TASTE
PTC tastes bitter to humans but not to mice. They can be cloned to find
the taste of PTC aversive.
CONCLUSION:
Both distributed and specificity (labelled line)
codes are involved in determining taste
taste thresholds
depend on:
1. temperature (different primaries alter differently)
2. Tongue region
salt
TASTE
THRESHOLDS
THRESHOLDS
sweet
sour
bitter
VARIATION WITH TEMPERATURE
VARIATION
OVER
TONGUE
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
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
neural pathway (uncrossed)
1 taste cells,
2 VII cranial nerves
(corda tympani division
of facial nerve), IX
cranial nerve
(glossopharyngeal),
3 solitary nucleus
4 ventral posterior medial
nucleus of thalamus,
5 taste cortex (near
mouth representation
of somatosensory
cortex)
TASTE PATHWAY
4. to
cortex
3. to
thalamus
also brain stem vomit centres
VII
IX
1. receptors
2. nerves
Taste
cortex
Central sulcus
TASTE AREA I
TASTE AREA II
Ventroposterior
medial
thalamus