Sensory Processes3270

Lecture 6

(chemical senses)

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.

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

AbducensVI

OculomotorIII

The 12 Cranial Nerves

1 olfactory2 optic3 oculomotor4 trochlear5 trigeminal6 abducens7 facial8 auditory and vestibular9 glossopharyngeal10 vagus11 accessory12 hypoglossal

VN VN

VI VI

IIIIII Oculomotor nuclei (III)

Abducens nuclei (VI)Vestibular nerve (VIII)

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

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

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 Processes3270

Chemical sensesTASTE

Taste primaries: sweet, sour, salty, bitter, umani

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

1. Tongue2. Papillae3. Taste buds4. Taste cells5. Receptors

THE TONGUE

(Filiform have no taste buds)

Glossopharyngeal (IX)

Chorda tympani (part of facial VII)

Bitter

Sour

Salt

Sweet

Fungiform

Foleate

Circumvallate

TASTE BUDS

TASTE BUDS

CODING in the TASTE SYSTEM

•Specificity (labelled lines)

or

•Distributed code ???

ammonium chloride

sodium chloride

potassium chloride

RESPONSES OF TASTE FIBRES TO DIFFERENT SALTS

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

saltsourbittersweetumani

• …. Each with different channel mechanisms• salt deprived salt cells quiet

salt type fibressweet type fibres

RESPONSES OF TASTE FIBRES

SPECIFICITY CODING IN TASTE

Sweet

Salt

Sour

Bitter

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

VARIATION WITH TEMPERATURE

VARIATIONOVER TONGUE

TASTE THRESHOLDSsalt

sweet

sour

bitter

TH

RE

SH

OL

DS

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 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

Ventro-posterior

medial thalamus

Taste cortex

Central sulcus

TASTE AREA I

TASTE AREA II