THE CHEMICAL SENSES
THE CHEMICAL SENSESAnimals depend on the chemical senses to identify nourishmentChemical sensation   Oldest and most commo...
TASTEThe Basics Tastes   Saltiness, sourness, sweetness, bitterness, and umami.   Innate preferences and rejections for pa...
TASTEThe Organs of Taste    Tongue, mouth, palate, pharynx, and epiglottis    Nasal cavity for smell
TASTEAreas of sensitivity on the tongue (but most of the tongue is sensitive to all basicstastes)     Tip of the tongue: S...
TASTETastes Receptor Cells     Apical end is the chemically sensitive part. It has small extensions called microvilli     ...
TASTETransduction: process by an environmental stimulus cause an electrical responsein a sensory receptor.In the case of t...
TASTESaltinessSpecial Na+ selective channel.The ion pass directly through channelcausing deporalizationSournessSourness- a...
TASTEBitternessBitter substances are detected by different typesT1R and T2R receptor. They work as G-proteincoupled recept...
TASTEBitterness   Sweetness   Umami
TASTE        VII Facial nerve        IX Glossopharyngeal nerve        X Vagus nerve        They carry primary gustatory   ...
SMELLSmell is not only important for taste but also for social communicationPheromones are important signals    •   Reprod...
SMELLThe Organs of Smell1)Olfactory epithelium: contains olfactory receptor cells, supporting cells (produce mucus),and ba...
SMELL  Olfactory TransductionReceptor potential: if strong enough generates APs in the cell body andspikes will propagate ...
SMELLAdaptation: decreased response despite continuous stimulus. Common features of sensoryreceptors across modalities    ...
SMELLCentral Olfactory PathwaysMapping of receptor cell into glomeruli is extremely precise
SMELLAxons of the olfactory tract branch and enter the forebrain (unconscious perception)bypassing the thalamusNeocortex (...
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Ch08

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Ch08

  1. 1. THE CHEMICAL SENSES
  2. 2. THE CHEMICAL SENSESAnimals depend on the chemical senses to identify nourishmentChemical sensation Oldest and most common sensory system with the aim to detect environmental chemicalsChemical senses Gustation & Olfaction (separate but processed in parallel) Chemoreceptors
  3. 3. TASTEThe Basics Tastes Saltiness, sourness, sweetness, bitterness, and umami. Innate preferences and rejections for particular tastes (sweet and bitter) have a survival reasons Usually there is correspondence between chemical ingredients and taste: Sweet—sugars like fructose, sucrose, artificial sweeteners (saccharin and aspartame) Bitter—ions like K+ and Mg2+, quinine, and caffeine Salty—salts Sour—acids How to distinguish the countless unique flavors of a food 1) Each food activates a different combination of taste receptors 2) Distinctive smell (it combines with taste to give the flavor) 3) Other sensory modalities (texture and temperature)
  4. 4. TASTEThe Organs of Taste Tongue, mouth, palate, pharynx, and epiglottis Nasal cavity for smell
  5. 5. TASTEAreas of sensitivity on the tongue (but most of the tongue is sensitive to all basicstastes) Tip of the tongue: Sweetness Back of the tongue : Bitterness Sides of tongues: Saltiness and sournessPapillae (taste receptors)FoliateVallateFungiformAt threshold concentration(just enough exposure ofsingle papilla to detect taste)they respond to only one taste.More concentrations lead toless selectivity
  6. 6. TASTETastes Receptor Cells Apical end is the chemically sensitive part. It has small extensions called microvilli that project into the taste pore. Receptor potential: Voltage shift – depolarization of the membrane cause CA++ entering the cell and release of transmitter
  7. 7. TASTETransduction: process by an environmental stimulus cause an electrical responsein a sensory receptor.In the case of taste, chemical stimuli (tastants) may:1)Pass directly through ion channels2)Bind to and block ion channels3)Bind to G-protein-coupled receptorsSlightly different mechanisms for saltiness, sourness, bitterness, sweetness andumami (amino acids)
  8. 8. TASTESaltinessSpecial Na+ selective channel.The ion pass directly through channelcausing deporalizationSournessSourness- acidity – low pHH + binds to and block ion channelscausing deporalization
  9. 9. TASTEBitternessBitter substances are detected by different typesT1R and T2R receptor. They work as G-proteincoupled receptorsSweetnessIt also detected by receptors T1R2+T1R thathave the same signaling mechanism (cf. bittertaste)The expressed in different taste cells allow thesystem not to be confused about the tasteUmamiUmami receptors T1R1+T1R3 detect aminoacids
  10. 10. TASTEBitterness Sweetness Umami
  11. 11. TASTE VII Facial nerve IX Glossopharyngeal nerve X Vagus nerve They carry primary gustatory axons Gustatory nucleus Point where taste axons bundle and synapse Ventral posterior medial nucleus (VPM) Deals with sensory information from the head Primary gustatory cortex (Insula) Receives axons from VPM taste neurons Lesion in VPM and Gustatory cortex can cause ageusia- the loss of taste perception
  12. 12. SMELLSmell is not only important for taste but also for social communicationPheromones are important signals • Reproductive behavior • Territorial boundaries • Identification • Aggression
  13. 13. SMELLThe Organs of Smell1)Olfactory epithelium: contains olfactory receptor cells, supporting cells (produce mucus),and basal cells (source of new receptor cells)2)Olfactory axons constitute olfactory nerve3)Cribriform plate: A thin sheet of bone through which small clusters of axons penetrate,coursing to the olfactory bulbAnosmia: Inability to smell
  14. 14. SMELL Olfactory TransductionReceptor potential: if strong enough generates APs in the cell body andspikes will propagate along the axon
  15. 15. SMELLAdaptation: decreased response despite continuous stimulus. Common features of sensoryreceptors across modalities Each receptor cell express a single olfactory receptor protein. They responds to different odours but with preferences. Many different cells are scattered into the epithelium
  16. 16. SMELLCentral Olfactory PathwaysMapping of receptor cell into glomeruli is extremely precise
  17. 17. SMELLAxons of the olfactory tract branch and enter the forebrain (unconscious perception)bypassing the thalamusNeocortex (conscious perception) is reached by a pathway that synapses in the medialdorsal nucleus of the thalamus

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