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Olfaction.docx

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Department
Psychology
Course
PSYC 2390
Professor
Lana Trick
Semester
Fall

Description
Olfaction 11/15/2012 4:32:00 PM Importance of Olfaction Macrosmatic: having a keen sense of smell is important for survival Microsmatic: having less keen sense of smell that is not crucial to their survival (humans)  Contact sense o Contact with molecules of the thing you are sensing  Connected with sense of esthetics (what is beautiful / ugly) o Rotting food  disgusting o Flowers  beautiful o Tied up in evaluation  Early warning system o Telling us about dangerous situations in the world o Can be useful in smelling other animals (good if you are predator / prey) o E.g. smelling fire, telling us when food is dangerous (bad milk)  Used in communication o Through pheromones (chemical signal release by individual that affects physiology / behaviour of another individual often without conscious awareness)  Communicate where territory is (cat rubbing up against you  marking you), sexual interest / readiness, emotional state (stressed out human being smell)  Smell and taste are related o Pinch nose to eat something (things taste different when you can’t smell them) o Aroma goes up back of throat into nasal cavity  Other uses: o Can be used to diagnose disease (different disorders have different smells)  TB  smell of stale beer  Kidney failure  smell of ammonia o Manufactures use this for sales  Smell closely associated with emotions and memory  New car smell - cause people to think car is newer or nicer than it actually is The Stimulus for Olfaction  Molecules that float in air (or water / fluid)  Some things don’t have smells o Substance must give off vapour (“sheds molecules”  Molecules must be fat soluble Physiology of Olfaction (structures, functions and associated problems) Nostrils:  Designed to sniff, bring in air o Optimal rate for sense of smell is 30m/minute  Important for sneezing o Protective mechanism o Get rid of things that are irritating (get rid of rapidly)  Nasal cycle o Nostrils take turns over the course of the day  2-3hrs, left nostril does most of work, then next 2-3hrs, right nostril does most of work  Can see this in terms of brain activity  Left nostril doing most of work  right olfactory system more active  One that is “on duty” is wider o Controlled by autonomic nervous system o Due to the fact that when cells are exposed to certain chemicals, need time to recover Nasal Cavity and Baffles:  3 bones (baffles)  Air is held, warmed up and moistened o Improves smell acuity  Allows air to be caught (around bones)  Hairs in nasal cavity removes a lot of dust etc.  Olfactory system works best in warm conditions (smell things best in warm, humid air  smells are more intense) Olfactory Mucosa (/ Epithelium):  One for each nostril  Size of dime on each case  On top of nasal cavity o Contains receptors for olfaction Supporting Cells  Secretes mucus o Contains olfactory binding protein (sticks molecules of odor on to mucus) Free Nerve Endings  Nerve sticking right down into mucosa  Basis of common chemical sense o Not olfaction proper o Combination between smell, taste and pain o Tangy smell (Vick’s vapour rub, ammonia, spicy foods  all stimulate common chemical sense) o Warning of danger  Something is a little bit toxic o If over stimulated…  Causes reflexive changes in breathing o Ozone also stimulates common chemical sense (smell in the mountains) Olfactory Receptor Neurons  Cilia o Move and get mucus moving (if it stayed in place, you wouldn’t be able to smell new things)  To expose neurons to different smells o Number varies between species  Humans  8 per neuron  Dogs  approx. 100 per neuron o Only case where you have brain cells in direct contact with the environment o Only kind of brain cells that degenerates  Die and are reborn every 5-7 weeks  Olfactory Receptors (OR) o This is where transduction takes place  Sensitive to certain / narrow range of chemical odorants o On the cilia  Contain olfactory receptor protein (critical to what it is you smell)  Different substances allow cell to pick up / absorb different things  Causes cell to take in Ca2+ ions  action potential  Over 350 kinds of receptor proteins  1 neuron has 1 type of protein (350 different types of olfactory receptor neurons) o Mice have 700-1000  Part of reason we can identify 100,000+ different odors Olfactory Nerve  Axons of neurons  Go through bone  cribform plate o Keeps axons (delicate) from getting banged together and thus damaged Olfactory Bulb  Where olfactory nerve comes to  Contains glomeruli o Different substances will produce different patterns of activity o All of 10,000 olfactory receptor neurons of a particular type send their signals to just one or two glomeruli  Each glomerulus collects information about the firing of a particular type of olfactory receptor neuron  Functional group associated with a particular type of compound determines the general area of the olfactory bulb that is activated and the compound’s chain length determines the position within each area  Activity is also related to the perceived odor Olfactory Tract  Information goes out olfactory bulb to olfactory tract Olfactory Cortex  Sense of smell is only sense that doesn’t go through the thalamus  Goes directly to olfactory cortex  Primary (information from olfactory tract) o A.k.a. piriform cortex  Responds at same rate of sniffing  Right nostril on duty  left piriform will be more active and vise versa  Perceiving complex odors that are created from overlapping activity of many different odorant molecules  Look to see how well rats can distinguish between a mixture and the component  When given enough time, neurons in piriform cortex can learn to discriminate between different odors o Might be involved in ability to tell difference between different odors in environment  Secondary (information from primary cortex) o A.k.a. orbital frontal cortex  Areas that identify what you are smelling  Evidence of top down effects (effects of expectations / knowledge)  Ambiguous smell  Condition 1 – tell them pleasant smell  Condition 2 – tell them unpleasant smell  More activity associated with smells with higher pleasantness ratings  Priming effects how the orbital cortex responds  Amygdala o Plays role in the emotional reactions that odors elicit Disorders of Olfaction 11/15/2012 4:32:00 PM Disorders of Olfaction Anosmia:  Smell blindness, lost sense of smell Temporary  Common cause is hard blows to the head o 3 bones condense and snip off axons o Killed olfactory receptor neurons  Can also do this if you inhale certain substances o Cocaine, zinc, anesthetics  Neurons regenerate every 5-7 weeks therefore sense of smell recovers (during that time, can’t smell anything) Permanent  General anosmia o Never goes away o Common cause is tumour in olfactory cortex  Specific types of anosmia o Blind to specific smells but can smell other things o 3% of population can’t smell scent of sweat o 47% can’t smell scent of urine o Some people can’t smell scent of skunk o Common cause is by not having all 350 kinds of olfactory receptor proteins  Everyone is probably missing a few (350 is a lot)
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