Sensation%20

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Sensation Perception (II) 3270 Lecture
7 smell
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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
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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,
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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
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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
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Sensory Processes 3270 Chemical senses SMELL
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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?

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DigiScents is developing this device, dubbed the
iSmell, to puff appropriate smells at you as you
surf the Web. Image courtesy of Digiscents, Inc.
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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!!
!
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An olfactometer
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Discrimination threshold
Weber Fractions Taste 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)..
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Episodic odours
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N of recall
Lab vision
Lab odours
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1 yr
time
RECALL OF ODOURS
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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
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THREE PARTS TO SMELL SYSTEM 1 --- OLFACTORY 2
--- VOMERONASAL 3 --- SOMATOSENSORY
--- trigeminal --- CHEMESTHESIS
--- texture, heat, irritation
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OLFACTORY BULB
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The olfactory mucosa
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OLFACTORY EPITHELIUM
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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.
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• 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.

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CONVERGENCE
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The olfactory receptor protein is a G protein.
It crosses the membrane 7 time. Similar to the
VISUAL PIGMENT. There are about 1000 variations.
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A bishops mitre
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Olfactory receptor Neurones
Mitral cells
Granule cells
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ZONES of the OLFACTORY MACULA glomerulus
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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
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• 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).

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

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

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Coding
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putrid
ethanol
fragrant
burned
resinous
spicy
HENNING SMELL PRISM
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• 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.

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• 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.)

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chemicals
Codes in olfactory receptors
fibres
across-fibre pattern coding
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This sort of coding means you can distinguish
many smells at once
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ZONES of the OLFACTORY MACULA glomerulus
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GLOMERULAR LAYER OF OLFACTORY BULB
(hot spots)
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Two similar compounds.
Radioactive deoxyglucose.
so there is an element of mapping there too
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Olfactory receptor Neurones
Mitral cells
Granule cells
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MULTIMODAL INFLUENCES
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smell and taste
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Multi-modal convergence in the ORBITOFRONTAL
CORTEX
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Neurone 1
Neurone 2
Orbito-frontal cortex bimodal cells
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cognitive factors same chemical, different
responses
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PHEROMONES the VOMERONASAL system
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VOMERONASAL SYSTEM
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VOMERONASAL SYSTEM
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VOMERONASAL SYSTEM
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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 Thal
amus Orbitofrontal cortex CODING Across-fibre
pattern coding, some mapping Increased
specificity of cells in cortex MULTISENSORY Visua
l, taste, olfaction, somatosensory VOMERONASAL Ac
cessory olfactory bulbs brainstem projection
pheromones
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Introduction to hearing under 2220_10 Speech
under 3270_(speech)
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KEYWORDS -- SMELL I
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 cellsplural glomeruli), convergence
(1,0001), 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
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KEYWORDS -- SMELL II
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
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KEYWORDS -- SMELL III
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
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KEYWORDS -- SMELL IV
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
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