Sensation & Perception (II)3270

Lecture 7

smell

KEYWORDS ---- TASTE I

Taste Primaries: sweet, sour, salty, bitter, papilla (nipple) types: fungiform (fungus-like), foliate (leaf-like), circumvallate (around the ramparts), taste buds (found on papilla), respond to more than one ‘primary' taste cells (found within taste buds), no axons, connect/synapse with afferent fibres

coding of quality, activity across a population, pattern of firing of nerves related to perceptual abilities in rats (responses to different salts, ammonium, potassium and sodium chloride), most fibres respond to more than one primary

KEYWORDS ---- TASTE II

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,

KEYWORDS ---- TASTE III

taste preferences, Humans: sweet (+); bitter (-), mostly in place at birth; Cats and 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, 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), brain stem vomit centres

The 12 Cranial Nerves

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

Sensory Processes3270

Chemical sensesSMELL

FUNCTIONS of SMELL

• Gatekeepers (good in, bad reject)• orient in space• mark territory• guide to find other animals• guide to find food• sex

• humans, perfumes indicate still important• detect spoiled food• fire• anosmia• sex?

DigiScents is developing this device, dubbed the iSmell, to puff appropriate smells at you as you surf the Web. Image courtesy of Digiscents, Inc.

Bloodhounds can pick up a 24hr old trail. Dogs have 1,000,000,000,000 olfactory receptors and we have about 10,000,000.

We can smell happiness and fear.

Everyone has an unique smell ..except identical twins!

Sniffer rats have been used to detectexplosives!!!

An olfactometer

Weber FractionsTaste 0.08 8%

Brightness 0.08 8% Loudness 0.05 5% Vibration 0.04 4% Line length 0.03 3% Heaviness 0.02 2% Electric shock 0.01 1%

For smell, can be as low as 5% (for n-butyl alcohol)..

Discrimination threshold

time 1 yr

N of recall

100%

60%

Episodic odours

Lab odours

Lab vision

RECALL OF ODOURS

HUMAN OLFACTORY ABILITIES

undershirts -- 75% identify themselves -- 75% identify genderinfants can identify mothers from milk smell

McClintock effect (synchonized menstrual cycles) -- works through sweat

THREE PARTS TO SMELL SYSTEM

1 --- OLFACTORY2 --- VOMERONASAL3 --- SOMATOSENSORY --- trigeminal --- CHEMESTHESIS --- texture, heat, irritation

OLFACTORY BULB

The olfactorymucosa

OLFACTORYEPITHELIUM

Olfactory receptor neurones---replaced every 60 days--- about 10,000,000 (in humans)

--- about 1,000 types

olfactory receptors (on the olfactory receptor neurones)--- about 1,000 types

olfactory binding proteins --- delivers odorants to receptor neurones.

Figure 15.5 (a) A portion of the olfactory mucosa. The mucosa contains 350 types of ORNs and about 10,000 of each type. The red circles represent 10,000 of one type of ORN, and the blue circles, 10,000 of another type. (b) All ORNs of a particular type send their signals to one or two glomeruli in the olfactory bulb.

CONVERGENCE

The olfactory receptor protein is a ‘G’ protein. It crosses the membrane 7 time.Similar to the VISUAL PIGMENT.There are about 1000 variations.

A bishop’s mitre

Olfactoryreceptor Neurones

Mitral cells

Granulecells

ZONES of the OLFACTORY MACULA& glomerulus

GLOMERULI

-- balls of tangled connections between MITRAL cells and OLFACTORY RECEPTOR NEURONES.

-- four zones (from macula)-- convergence (about 1,000 to 1)-- olfactory receptor types kept organized-- properties sharpened by lateral inhibition

-- send information to ANCIENT paleocortex

Figure 15.9 (a) The underside of the brain, showing the neural pathways for olfaction. On the left side, the temporal lobe has been deflected to expose the olfactory cortex. (Adapted from Frank & Rabin, 1989).

mitral cells in the olfactory bulb

olfactory receptor neurones

piriform cortex

amygdala

thalamus

orbitofrontal cortex

conscious discrimination

emotional response

Figure 15.10 Flow diagram of the pathways for olfaction. (From Wilson and Stevenson, 2006)

thalamus

conscious discrimination

emotional response

Coding

putrid

ethanol

resinousspicy

fragrant

burned

HENNING SMELL PRISM

Figure 15.2 (a) Two molecules that have the same structures, but one smells like musk and the other is odorless. (b) Two molecules with different structures but similar odors.

Figure 15.6 Recognition profiles for some odorants. Large dots indicate that the odorant causes a high firing rate for the receptor listed along the top; a small dot indicates a lower firing rate for the receptor. The structures of the compounds are shown on the right. (Adapted from Malnic et al., 1999.)

Codes in olfactory receptors

fib

res

chemicals

across-fibre pattern coding

This sort of coding means you can distinguish many smells at once

ZONES of the OLFACTORY MACULA& glomerulus

GLOMERULAR LAYER OFOLFACTORY BULB

(hot spots)

Radioactive deoxyglucose.

Two similar compounds.

… so there is an element of mapping there too

Olfactoryreceptor Neurones

Mitral cells

Granulecells

MULTIMODAL INFLUENCES

smell and taste

Multi-modal convergence in the ORBITOFRONTAL CORTEX

Orbito-frontal cortex: bimodal cells

Neurone 1

Neurone 2

cognitive factors: same chemical, different responses

PHEROMONES & the VOMERONASAL system

Moth

VOMERONASAL SYSTEM

VOMERONASAL SYSTEM

VOMERONASAL SYSTEM

SUMMARYFunctions of smell; Emotional contentPATHWAYS

Olfactory binding proteinOlfactory receptor neuronesGlomerulus of mitral cells

convergence, lateral inhibition, zonesAncient paleocortex (piriform)AmygdalaThalamusOrbitofrontal cortex

CODINGAcross-fibre pattern coding, some mappingIncreased specificity of cells in cortex

MULTISENSORYVisual, taste, olfaction, somatosensory

VOMERONASALAccessory olfactory bulbs; brainstem projection; pheromones

Introduction to hearing under 2220_10Speech under 3270_(speech)

olfactory binding protein, olfactory receptors cells continuously regenerate (about every 60 days), cilia (on olfactory receptor cells), glomerulus (contact zones between receptor cells and mitral cells:plural glomeruli), convergence (1,000:1), mitral cell, olfactory tubercle of entorhinal cortex (part of paleocortex), medial dorsal nucleus of thalamus , olfactory neocortex

paleocortex associated with limbic system, limbic system associated with emotions (electrical stimulation causes sham rage), limbic system associated with memories (H.M. had lesions here and lost the ability to memorize things), no topographic mapping in olfactory cortex (unusual), some hot spots in olfactory tubercle and on olfactory mucosa

KEYWORDS -- SMELL I

odour quality, no primaries identified in olfactory system, poor tuning of receptors (to chemicals or chemical types) (sharpened by lateral inhibition, inhibitory interneurones, granule cells), Henning smell prism, stereochemical theories based on lock and key partially successful, BUT no receptor sites identified, similar shaped molecules can be associated with different smell perceptions

cells broadly tuned (responding to many different chemicals associated with many different smells)

codingintensity= firing rate/recruitment, quality = distributed pattern code, problems in identifying many smells at once, binding problem

KEYWORDS -- SMELL II

odour thresholds, olfactorium; unique technical problems!, humans very sensitive (eg. mercaton can be detected at 1 part per 50,000,000,000), affected by gender; can be affected by menstrual cycle, affected by age

adaptation, thresholds raised (by exposure), masking (by other chemicals), some cross effects: eg. adapting to orange affects smell of lemons

identification, can identify gender from shirt, prefer own odours, odour memories long lasting; associated with emotions (via limbic system) "designed not to forget”, pheromones, releasers (immediate effect), eg. bitch on heat, territorial markers, humans?, McClintock effect (synchronized menstrual cycles), primers (longer term) eg. mice need males around for proper oestrus cycles

KEYWORDS -- SMELL III

PATHWAYS olfactory receptor cells to mitral cells in olfactory bulb to olfactory tubercle in paleocortex THEN

1 to medial dorsal thalamus to olfactory cortex

(ORBITOFRONTAL CORTEX) 2 to limbic system 3 brain stem pathways associated with pheromones

ALSO

inhibitory pathway (via inhibitory interneurone: granule cells) from one olfactory bulb to the other to do with detecting the DIRECTION from which a smell originates

KEYWORDS -- SMELL IV