OLFACTION

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Olfaction is very important for us and also for other animals.

Dog’s sense of smell is 1000 times more than humans. People use dog’s keen sense of smell in many ways---
Govt. agencies use specially trained dogs in search and rescue missio
Detection of narcotics.
Detection of forensic cadaver material.

Due to lack of smell the following disorders may be seen---
Anosmia : lack of ability to smell
Hyposmia- decreased ability to smell
Phantosmia- [“hallucinated smell”] often unpleasant in nature
Dysosmia- things smell differently than they should.
Hyperosmia- an abnormally acute sense of smell

Some times olfaction serve as marker for Perkinson’s diseases. Some illness can be diagnosed by their associated smell( e.g. acetone and diabetes). So smell therapy and clinical use of odour is an area for future.

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OLFACTION

  1. 1. OLFACTIONOLFACTIONSARAMITA DESARAMITA DECHAKRAVARTICHAKRAVARTIResearch AssistantResearch AssistantChembiotech Research LaboratoriesChembiotech Research LaboratoriesWorcestershire, United KingdomWorcestershire, United Kingdom
  2. 2. What is Olfaction ?What is Olfaction ?Olfaction (the sense of smell i.e., the detection ofOlfaction (the sense of smell i.e., the detection ofsmall molecules in the air ) is one of the mostsmall molecules in the air ) is one of the mostancient sense, which allows vertebrates andancient sense, which allows vertebrates andother organisms with olfactory receptors toother organisms with olfactory receptors toidentify food, mates, predators and provide bothidentify food, mates, predators and provide bothsensual pleasure (the odour of flowers andsensual pleasure (the odour of flowers andperfume) as well as warning of danger (spoiledperfume) as well as warning of danger (spoiledfood, chemical dangers).food, chemical dangers).
  3. 3. A Wide Variety of Organic Compounds areA Wide Variety of Organic Compounds areDetected by OlfactionDetected by OlfactionHuman beings can detect and distinguish thousand ofdifferent compounds by smell, often with considerablesensitivity and specificity. Most odourants are relativelysmall organic compounds with sufficient volatility and theycan be carried as vapours into the nose.Figure 1 : Structure of different organic molecule
  4. 4. The shape of the molecule rather than itsThe shape of the molecule rather than itsother physical properties is crucialother physical properties is crucialFigure2 : Structure of different organic molecule
  5. 5. General Physiology of OlfactionGeneral Physiology of Olfaction The olfactory region consist of ciliaThe olfactory region consist of ciliaprojecting down, out of the olfactoryprojecting down, out of the olfactoryepithelium into a mucous layer.epithelium into a mucous layer. The mucous layer is produced byThe mucous layer is produced byBowman’s gland, which resides inBowman’s gland, which resides inthe olfactory epithelium.the olfactory epithelium. Odorants are volatile chemicalOdorants are volatile chemicalcompounds, carried out by inhaledcompounds, carried out by inhaledair to the Regio olfactoria (Olfactoryair to the Regio olfactoria (Olfactoryepithelium) located in the roof ofepithelium) located in the roof ofthe two nasal cavities of the nose.the two nasal cavities of the nose. In the olfactory epithelium, olfactoryIn the olfactory epithelium, olfactoryreceptor neurons are present. Eachreceptor neurons are present. Eacholfactory receptor neurons have 8-olfactory receptor neurons have 8-20 whip like ciliary projection.20 whip like ciliary projection.Figure 3: The Main Nasal Epithelium
  6. 6.  The olfactory receptor neurons extend through the epithelium to contact odorants inThe olfactory receptor neurons extend through the epithelium to contact odorants inthe atmosphere, on the opposite side within the epithelium, the neuronal cells formthe atmosphere, on the opposite side within the epithelium, the neuronal cells formaxons that are bundled in groups of 10-100 to penetrate the ethmoidal cribriformaxons that are bundled in groups of 10-100 to penetrate the ethmoidal cribriformplate of bone, reaching the olfactory bulb of the brain where they converge toplate of bone, reaching the olfactory bulb of the brain where they converge toterminate with post-synaptic cells to form synaptic structures called glomeruli. Theterminate with post-synaptic cells to form synaptic structures called glomeruli. Theglomeruli are connected in groups that converge into mitral cells.glomeruli are connected in groups that converge into mitral cells. Physiologically, this convergence increases the sensitivity of the olfactory signalPhysiologically, this convergence increases the sensitivity of the olfactory signalsent to the brain. From the mitral cells the message is sent directly to the highersent to the brain. From the mitral cells the message is sent directly to the higherlevels of the central nervous system in the corticomedial amygdala portion of thelevels of the central nervous system in the corticomedial amygdala portion of thebrain (via the olfactory nerve tract) where the signaling process is decoded andbrain (via the olfactory nerve tract) where the signaling process is decoded andolfactory interpretation and response occurs.olfactory interpretation and response occurs.Figure4 : Cells and connection of olfactory epithelium and olfactory bulb
  7. 7. The Trigeminal Sense in theThe Trigeminal Sense in theOlfactory EpitheliumOlfactory EpitheliumIt must also be recognized that the olfactory epithelium containsanother sensory system in the form of "Trigeminal Nerve" receptors,present in mouth, eyes and nasal cavity.A number of trigeminal chemical stimulants produce effectsdescribed as hot, cold, tingling or irritating. For examples ---ChemicalsChemicalsleavo menthol or (-) menthol cold (at moderateleavo menthol or (-) menthol cold (at moderateconcentration)concentration)hot (at high concentration)hot (at high concentration)allyl isothiocyanate --- mustard, mustard oilallyl isothiocyanate --- mustard, mustard oilcapciacin --- hot Chile powder, mace spraycapciacin --- hot Chile powder, mace spraydiallyl sulfide --- oniondiallyl sulfide --- onion
  8. 8. The Odorant BindingThe Odorant Binding ProteinsProteinsIn 1979, Steven Price & coworkers and later Fesenko. et. al. found a number ofIn 1979, Steven Price & coworkers and later Fesenko. et. al. found a number of“Odorant Binding Protein” (OBP) for odorant chemicals such as ---“Odorant Binding Protein” (OBP) for odorant chemicals such as ---5-a-ANDROST-16-EN-3-ONEFigure 5 : Different odourant binding protein
  9. 9. Function Of OBPFunction Of OBP They bind lipophilically to odorants inThey bind lipophilically to odorants inthe aqueous / lipid mucousthe aqueous / lipid mucousincreasing the concentration andincreasing the concentration andfacilitate in transport.facilitate in transport. They bind to ligand and receptors &They bind to ligand and receptors &assist in transport.assist in transport. They act as a kind of filter to preventThey act as a kind of filter to preventexcessive amounts (over stimulation)excessive amounts (over stimulation)from reaching the receptors.from reaching the receptors. The role of OBPs become clear inThe role of OBPs become clear in2000 with characterization of human2000 with characterization of humanlipocalins involvement in odorantslipocalins involvement in odorantsbindings.bindings.Figure 6: Partial structure ofFigure 6: Partial structure ofHuman OPB IIaHuman OPB IIamodeled against 1EW3A (CRYSTALmodeled against 1EW3A (CRYSTALSTRUCTURESTRUCTUREOF THE MAJOR HORSE ALLERGENOF THE MAJOR HORSE ALLERGENEQU C 1)EQU C 1)
  10. 10. Odorant or olfactory receptor (OR)Odorant or olfactory receptor (OR) In 1991, Linda Buck andIn 1991, Linda Buck andRichard Axel discoveredRichard Axel discoveredboth the family ofboth the family oftransmembrane proteins,transmembrane proteins,called odorant receptors.called odorant receptors.The proteins contained the 7The proteins contained the 7helical transmembranehelical transmembranestructure and have sequencestructure and have sequencesimilarity to other memberssimilarity to other membersof the G-protein family.of the G-protein family. Recently (2000), DoronRecently (2000), DoronLancet & co-workers at theLancet & co-workers at theWeizmann Institute ofWeizmann Institute ofScience Crown HumanScience Crown HumanGenome Center haveGenome Center haveconstructed a database ofconstructed a database ofhuman olfactory receptorhuman olfactory receptorgenes present in differentgenes present in differentchromosomes.chromosomes.Figure 7 : 7-transmembrane olfactory receptor
  11. 11. Figure 8 : Human olfactory receptor genes by chromosome location
  12. 12. Molecular events in OlfactionMolecular events in Olfaction The olfactory stimulus arrives at the sensory cells by diffusion through air. The odorant molecule binds directly to an olfactory receptors or to a specificbinding protein that carries the odorant to a receptor. Interaction between odorant and the receptor triggers a change in receptorconformation that result in the replacement of bound GDP by GTP on G-protein (Golf). The activated Golf then activates adenyl cyclase of the ciliary membrane,which synthesize cAMP from ATP, raising local [cAMP]. The cAMP gated Na+and Ca++channels of the ciliary membrane open and theinflux of Na+ and Ca++produce a small depolarization called receptorpotential. if a sufficient number of odorant molecules encounter receptors, thereceptor potential is strong enough to cause the neuron to fire an actionpotential. This relayed to brain in several stages and registers as a specificsmell. These events occur within 100-200 ms.
  13. 13. Figure 9 : Molecular events of Olfaction
  14. 14. Other second messengers inOther second messengers inolfactionolfaction Inositol triphosphate (IPInositol triphosphate (IP33)actively participate in)actively participate inolfactory transduction with in certain mammals.olfactory transduction with in certain mammals. Recent evidence is that the cAMP is mediated byRecent evidence is that the cAMP is mediated byanother cyclic nucleotide cGMP.another cyclic nucleotide cGMP. NO modulate cGMP concentration in mitral cells.NO modulate cGMP concentration in mitral cells. Similarly carbon monoxide (CO) serves as aSimilarly carbon monoxide (CO) serves as agaseous neuronal messenger linked to cGMPgaseous neuronal messenger linked to cGMPproduction.production.
  15. 15. ConclusionConclusionSo from this discussion we can say that olfaction is very important forSo from this discussion we can say that olfaction is very important forus and also for other animals.us and also for other animals.Dog’s sense of smell is 1000 times more than humans. People useDog’s sense of smell is 1000 times more than humans. People usedog’s keen sense of smell in many ways---dog’s keen sense of smell in many ways---i.i. Govt. agencies use specially trained dogs in search and rescueGovt. agencies use specially trained dogs in search and rescuemissiomissioii.ii. Detection of narcotics.Detection of narcotics.iii.iii. Detection of forensic cadaver material.Detection of forensic cadaver material.Due to lack of smell the following disorders may be seen---Due to lack of smell the following disorders may be seen---Anosmia : lack of ability to smellAnosmia : lack of ability to smellHyposmia- decreased ability to smellHyposmia- decreased ability to smellPhantosmia- [“hallucinated smell”] often unpleasant in naturePhantosmia- [“hallucinated smell”] often unpleasant in natureDysosmia- things smell differently than they should.Dysosmia- things smell differently than they should.Hyperosmia- an abnormally acute sense of smellHyperosmia- an abnormally acute sense of smellSome times olfaction serve as marker for Perkinson’s diseases. SomeSome times olfaction serve as marker for Perkinson’s diseases. Someillness can be diagnosed by their associated smell( e.g. acetone andillness can be diagnosed by their associated smell( e.g. acetone anddiabetes). So smell therapy and clinical use of odour is an area fordiabetes). So smell therapy and clinical use of odour is an area forfuture.future.
  16. 16. AcknowledgementAcknowledgement Thanks to Dr. Prof John Kerry, University of London for giving meconstant encouragements and suggestions whenever it is necessary. Other Professors and Scholars of my department, to whom I amindebted for various courtesies. The liberal assistance of the non – teaching staffs and technicalassistance of our Technical Assistant of our Department is alsoacknowledged. I am thankful to my entire colleagues for encouragement andappreciations and their co – operations. Lastly, but not the least, I would like to express my gratitude to myparents and my sister for their constant encouragements andblessings on me.
  17. 17. Thank YouThank You

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