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Lecture 12

Lec12 - Olfaction and Taste - Apr4.docx

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Matthias Neimier

PSYB51-Lec 12 th Friday April 4 , 2014 Olfaction and Taste; Spatial orientation and the Vestibular System Olfaction & Taste • Considered chemical senses • Olfactory physiology • From chemical to smells • Olfactory psychophysics • Olfactory hedonics • Olfaction, memory, and emotion • Anatomy and physiology of taste • The five basic tastes • Taste versus flavor o Flavour is actually a smell… has to do with the nose • Vestibular system Olfaction: Introduction • Immanuel Kant on smell o Most important philosopher of 18 century o Didn’t think smell was very important o Probably due to the fact that their sewer systems were not very functionable o It’s actually very important • IKEA o Companies know how to use smell to their advantage o Walking into IKEA, it smells like fresh wood…. Suggesting furniture is good quality  It’s actually fake… just perfume o Uses that to influence us and suggest something that is not true • Attention o All senses run through the thalamus o Smell doesn’t o We have very little control of what we can and cannot smell • Language o Difficult to name things that have a certain smell • Sex Olfactory Physiology • A look at the olfactory apparatus • Genes and olfaction • Multisensory perception • Physical event that is processes by receptors, than the brain • Chemical events • Odors: olfactory sensations o Chemical compounds that are…  Volatile • Fly through the air… so it can reach your nose  Small  Hydrophobic • Chemical properties that allow molecules to bind to olfactory area o But not all  Can’t smell methane/ Carbon monoxide  Can be lethal • We have detectors in our noses • The human olfactory apparatus: • Nose: small ridges (nasal cycle) • Ridges create turbulences • Sniffing o To enhance smell o Make smells richer and clearer • Olfactory cleft, olfactory epithelium o Have a bunch of olfactory receptors that fish for molecule to be processed • Secondary purpose of the nose o First purpose is for breathing • The olfactory epithelium: the “retina” of the nose contains 3 types of cells:  Equivalent to retina in the eye 1. Supporting cells 2. Basal cells (precursors to…) 3. Olfactory sensory neurons (OSNs) – cilia protruding into mucus covering olfactory epithelium  Hairs imbedded in here (cilia) o Olfactory receptors (ORs): interact with odorants  action potentials along… o Olfactory nerve (cranial nerve I; thin axons, slow) • Axon bundles are the first cranial nerve • Small bundles that are distributed • Has little holes in it for axons of olfactory neuron enter from the olfactory epithelium and into the brain o Essentially like a sieve o Like hairs on the head of a toothbrush • Electric razor… has two layers that create shearing forces o Applied for olfactory system • When head is forcefully decelerated… inside head… your brain will hit the inside of your skull o As brain moves… olfactory nerves get sheared o Lose sense of smell… really bad • Lesions to olfactory nerve cause anosmia: o Head trauma (cribriform plate)  Hard for axons to regrow  Usually in severe car accidents o Infections • Olfactory loss can cause great suffering: o Affects emotions o Sense of taste/flavour o Danger warning  Can’t smell if something is burning • Quite common • Early symptom for Alzheimer’s, Parkinson’s o Just one symptom amongst many o Having poor smell doesn’t indicate these diseases • the olfactory bulb: • ipsilateral projection o tip of olfactory bulb o no cross over with other senses • glomeruli: spherical structures in which OSNs synapse with mitral cells and tufted cells • chemo-topography : glomeruli sort according to ORs o organized fairly regularly • olfactory cortex • amygdala-hippocampal complex • entorhinal cortex • smell has a lot to do with emotions • we remember smells extremely well • doesn’t run through the thalamus • the genetic basis of olfactory receptors: o ~1000 different olfactory receptor genes, each codes for single type of OR  Each receptor has its own genes  Most of these genes… we would never use o Pseudogenes: dormant, don’t produce proteins (I.e., Ors), 20% in dogs, 60-70% in humans  Olfaction much better in dogs o Trade-off between vision and olfaction?  Because dogs don’t have very good vision, they have better smell  And vice versa for humans • Multisensory perception: a feel of scent: o Odorants can stimulate somatosensory system (touch, pain, temperature receptors)  Smelling something peppery… you smell... but also feel pain (tickling in nose) o These sensations are mediated by the trigeminal nerve (cranial nerve V)  Somatosensation for the face o Also see taste!  Smell and flavor go together Olfaction & Taste • From Chemicals to Smells o Shape-pattern theory o Odor mixtures From chemicals to smells • Shape-pattern theory: match between shapes of odorants and odor receptors (key & lock); dominant biochemical theory o Molecules that float through the air and bind to receptors in olfactory epithelium o 3-d structure o Goes into olfactory structure like a lock o recent molecular research: scents are detected by means of combinatorial codes  lock and key  similarly shaped o All sorts of random shapes...can fit in different orientation into olfactory receptors • the importance of patterns: o We detect a multitude of scents based on ‘only’ 300-400 olfactory receptors… how?  The molecules can orient themselves to fit in different receptors  Very flexible in terms of which lock and key they can fit into o We can detect the pattern of activity across various receptor types o Similar to metameres in colour vision: phenyl ethyl alcohol = rose  Can’t tell the difference between truly yellow light and a mix of blue and green light  Because we only have space for a few colour receptors in retina (3)  Practical for computer scenes… can’t have too many pixels o The chemical smells like roses… because the odor molecules are similar o Have to deal with complex things… but we only have 300-400 olfactory receptors • Odor mixtures: o we rarely smell “pure odorants,” rather we smell mixtures  similar to having different wavelengths in sound o How do we process the components in a mixture of odorants? o Two possibilities: 1. Analysis (audition: hi/low pitched tones) 2. Synthesis (metameres in colour vision) o Olfaction rather synthetic but can be trained Olfaction & Taste cont’d • Olfactory psychophysics • Differences between detection – discrimination – recognition • How do we adapt to smells? Olfactory Psychophysics, Identification and Adaptation • Olfactory detection thresholds: depend on several factors, e.g., length of carbon chains (vanilla!) o Small molecules… but vanilla has a long carbon change o We can easily detect it’s smell • Women: lower thresholds than men, depending on menstrual cycles but not pregnancy o More sensitive to smell… like colour • New research suggests that humans can distinguish at least 1trillion olfactory stimuli (1 000,000,000, 000) o Previously, they thought professionals can distinguish up to 100, 000 odors (e.g., professional perfumers, wine tasters) – the textbook is wrong o Smell can be trained o We can extrapolate and get a trillion out of different tests o This study shows even just normal people can smell so many different scents • Yet another dream job… o Professional smellers that test deodorant on people • Recognition: smell and memory • Durability: our recognition of smells is durable even after several days, month, or year o You never forget a smell o Can remember a smell from childhood o Smells can remind you of something you have seen or experienced • Identification: smell and language  Ability to name things related to smell o Attaching verbal label to smell is not easy (few words for smell)  Disjoint o “tip –of-the-nose phenomenon”  Smell something… that you recognize… but you can’t say what it is o Disconnect btw. Language and smell (left vs. right brain)  Smell with right hemisphere, while language is left hemisphere? • Probably not o Patrick Suskind: The Perfume  Story uses language to describe smell • Adaptation: o Sense of smell is essentially a change detector o e.g., walking into baker, plumber  plumbers use their nose to do their job o odors bind to G protein –coupled receptors that indirectly open Na+ channels  during adaptation the continuous stimulation through odors of the GPCRs, bury themselves into the membrane of the cilia of the olfactory sensory neurons  they become less sensitive to these sensors o receptor adaptation: continuous stimulation; GPCRs bury themselves inside cells o intermittent stimulation: e.g., wood smell at IKEA  ikea wants you to smell that all the time  have little wells of perfumes in their hall and puffs out perfume occasionally  helps reduce adaptation o Cross adaptation: reduced detection of odor after exposure to odors that stimulate the same ORs  Smelling lotions, smell a bowl of coffee beans to “clean” the nose • Cognitive (and other kinds of) habituation: after long-term exposure to an odorant, one has very diminished detection ability o after returning from vacation house has smell  you are less habituated to the smells in your house after a week of vacation o long-term (not necessarily cognitive) mechanisms 1. longer term receptor adaptation • stimulate senses for a long period of time 2. odorant molecules may be absorbed into bloodstream causing adaption to continue • you smell like your house • when you eat a lot of garlic… you will smell like garlic • odors enter your bloodstream • you can’t smell yourself that well 3. cognitive-emotional factors • when you have the impression that the odor is harmful, you will adapt less  * odors believed to be harmful won’t adapt Olfaction & Taste cont’d • What makes us (dis)like smells? Olfactory Hedonics o Familiarity vs. intensity o Nature vs. nurture Olfactory Hedonics • Odor hedonics: the liking dimension of odor perception; typically measured with scales pertaining to an odorant’s perceived pleasantness, familiarity, and intensity o Degree to which we enjoy/not enjoy certain smells o Use psychophysical methods to test that o Plot graph with how intense certain smells are o Can put too much perfume on yourself and people will not like this • Not all smells are enjoyed • We tend to like odors we’ve smelled many times before (nurture!) o Being more familiar to the smells as opposed to smells we don’t really know • Influence of intensity Olfaction & Taste cont’d • Chemical sensation in the body • Anatomy and physiology • The five basic tastes • Taste versus flavor Anatomy and Physiology • Taste buds: • Create neural signals conveyed to brain by taste nerves • Embedded in structure: papillae (bumps on tongue) o Increase surface of tongue o Increase grip on food o Inside papillae are taste buds • Each taste bud contains taste receptor cells o Has multiple receptors • Information is sent to brain via cranial nerves • Papillae: Four kinds o Filiform papillae: anterior portion of tongue; without any taste function o Fungiform papillae: resemble tiny mushrooms, on anterior part of tongue, visible o Foliate papillae: on sides of tongue, look like series of folds o Circumvallate papillae: large circular structures Taste Receptor Cell Mechanisms • 2 types of tastants: o Channels for salty & sour  Channels opening and closing  Physical fusion of neurotransmitters with synaptic cleft … o G protein-coupled receptors  Similar to smell; secondary messenger system; indirectly causes depolarization • Directly causes depolarization • 5 different tastes o o Salty o Sour o Sweet o Bitter o Umami Anatomy and Physiology cont’d • Central nervous system: • Facial nerve/chorda tympani (VII), glossopharyngeal nerve (IX), Vagus nerve (X) o Vagus nerve: so many different functions… vague as to what it does • Gustatory information travels through medulla and thalamus to cortex • Primary cortical processing area for taste: insular cortex o Piece of frontal cortex right behind the temporal cortex o Insulates from everything else • Orbitofrontal cortex: receives projections from insular cortex • some orbitofrontal neurons are multimodal • the pathway Olfaction & Taste cont’d • The Five Basic tastes o Either super-complex or extremely simple • Salty: o Salt made up of two particles: Cation (+anion) o Sodium saccharine  Salt even though anion is saccharine (which is sweet) o Ability to perceive salt & liking: not static  We can adapt to it o Gestational experiences may affect liking for saltiness  Also affected when you are a fetus  If mother eats a lot of salty food, babies will enjoy salt as well • Sour: o Acidic substances o At high concentrations, acids will damage both external and internal body tissues  Could be harmful if you eat too much • Bitter: o Quinine: prototypically bitter-tasting substance  Many things taste bitter o Cannot distinguish between tastes of different bitter compounds  Can’t tell the different between bitter … it just is o Many bitter substances are poisonous  The taste warns you
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