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Sensation & Perception (II) 3270 Lecture 7 smell.

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1 Sensation & Perception (II) 3270 Lecture 7 smell

2 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

3 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,

4 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

5 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

6 Sensory Processes 3270 Chemical senses SMELL

7 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?

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

9 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 detect explosives!!!

10 An olfactometer

11 Weber Fractions Taste0.08 8% Brightness0.088% Loudness0.055% Vibration0.044% Line length0.033% Heaviness0.022% Electric shock0.011% For smell, can be as low as 5% (for n-butyl alcohol).. Discrimination threshold

12 time 1 yr N of recall 100% 60% Episodic odours Lab odours Lab vision RECALL OF ODOURS

13 HUMAN OLFACTORY ABILITIES undershirts -- 75% identify themselves -- 75% identify gender infants can identify mothers from milk smell McClintock effect (synchonized menstrual cycles) -- works through sweat



16 The olfactory mucosa


18 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.

19 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.


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



24 A bishop’s mitre


26 Olfactory receptor Neurones Mitral cells Granule cells

27 ZONES of the OLFACTORY MACULA & glomerulus

28 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

29 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).

30 mitral cells in the olfactory bulb olfactory receptor neurones piriform cortex amygdala thalamus orbitofrontal cortex conscious discrimination emotional response


32 Figure Flow diagram of the pathways for olfaction. (From Wilson and Stevenson, 2006) thalamus conscious discrimination emotional response

33 Coding

34 putrid ethanol resinous spicy fragrant burned HENNING SMELL PRISM

35 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.

36 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.)

37 Codes in olfactory receptors fibres chemicals across-fibre pattern coding

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

39 ZONES of the OLFACTORY MACULA & glomerulus


41 Radioactive deoxyglucose. Two similar compounds. … so there is an element of mapping there too

42 Olfactory receptor Neurones Mitral cells Granule cells



45 smell and taste

46 Multi-modal convergence in the ORBITOFRONTAL CORTEX

47 Orbito-frontal cortex: bimodal cells Neurone 1 Neurone 2

48 cognitive factors: same chemical, different responses






54 SUMMARY Functions of smell; Emotional content PATHWAYS Olfactory binding protein Olfactory receptor neurones Glomerulus of mitral cells convergence, lateral inhibition, zones Ancient paleocortex (piriform) Amygdala Thalamus Orbitofrontal cortex CODING Across-fibre pattern coding, some mapping Increased specificity of cells in cortex MULTISENSORY Visual, taste, olfaction, somatosensory VOMERONASAL Accessory olfactory bulbs; brainstem projection; pheromones

55 Introduction to hearing under 2220_10 Speech under 3270_(speech)

56 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

57 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) coding intensity= firing rate/recruitment, quality = distributed pattern code, problems in identifying many smells at once, binding problem KEYWORDS -- SMELL II

58 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

59 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


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