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