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

VN VI III 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 -> 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 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 Processes 3270 Chemical senses TASTE

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

Figure The contribution of each of the four basic tastes to the tastes of KCl and NaNO 3, 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.) MAGNITUDE ESTIMATION

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

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 salt sour bitter sweet umani …. Each with different channel mechanisms salt deprived  salt cells quiet

salt type fibres sweet 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 VARIATION OVER TONGUE TASTE THRESHOLDS salt sweet sour bitter THRESHOLDS

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) 1taste cells, 2VII cranial nerves (corda tympani division of facial nerve), IX cranial nerve (glossopharyngeal), 3solitary nucleus 4ventral posterior medial nucleus of thalamus, 5taste cortex (near mouth representation of somatosensory cortex) also brain stem vomit centres 1. receptors 2. 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