04 The Chemical Senses

1. 04 The Chemical Senses Psychology 355

2. Introduction • Animals depend on the chemical senses to identify nourishment • Chemical sensation • Oldest and most common sensory system • Chemical senses • Gustation • Olfaction • Chemoreceptors Psychology 355

3. Taste The Basics Tastes • Saltiness • sourness, • sweetness, • bitterness, and • Umami Examples of correspondence between chemistry • Sweet—sugars like fructose, sucrose, artificial sweeteners (saccharin and aspartame) • Bitter—ions like K+ and Mg2+, quinine, and caffeine • Sour— Acidity (low Ph), H+ • Salt—Na+ Psychology 355

4. Taste Advantage – Survival: Poisonous substances - often bitter Single-Trial Learning; Self-Balancing Diet Psychology 355

5. Taste The Basics Tastes • Saltiness • sourness, • sweetness, • bitterness, and • Umami chemistry • Sweet—sugars like fructose, sucrose, artificial sweeteners (saccharin and aspartame) • Bitter—ions like K+ and Mg2+, quinine, and caffeine • Sour— Acidity (low Ph), H+ • Salt—Na+ Advantage – Survival: Poisonous substances - often bitter Psychology 355

6. Taste The Basics Tastes • Saltiness • sourness, • sweetness, • bitterness, and • Umami chemistry • Sweet—sugars like fructose, sucrose, artificial sweeteners (saccharin and aspartame) • Bitter—ions like K+ and Mg2+, quinine, and caffeine • Sour— Acidity (low Ph), H+ • Salt—Na+ Advantage – Survival: Poisonous substances - often bitter Psychology 355

7. Taste The Basic Tastes • Steps to distinguish the countless unique flavors of a food • Each food activates a different combination of taste receptors • Distinctive smell • Other sensory modalities Psychology 355

8. Taste The Organs of Taste Tongue, mouth, palate, pharynx, and epiglottis Psychology 355

9. Taste Areas of sensitivity on the tongue • Tip of the tongue Sweetness • Back of the tongue Bitterness • Sides of tongues Saltiness and sourness Psychology 355

10. Taste The Organs of Tastes • Papillae • Foliate papillae • Vallate papillae • Fungiform papillae Threshold concentration Just enough exposure of single papilla to detect taste Psychology 355

11. Taste • Tastes Receptor Cells • Apical ends Microvilli Taste pore • Receptor potential: Voltage shift Psychology 355

12. Taste Mechanisms of Taste Transduction • Transduction process • Taste stimuli (tastants) • Pass directly through ion channels (Na+) • Bind to and block ion channels (sour-H+) • Bind to G-protein-coupled receptors (bitter, sweet, umami) Psychology 355

13. Taste Mechanisms of Taste Transduction Saltiness • Salt-sensitive taste cells • Special Na+ selective channel • Blocked by the drug amiloride Psychology 355

14. Taste Mechanisms of Taste Transduction Sourness • Sourness- acidity – low pH • Protons causative agents of acidity and sourness Psychology 355

15. Taste Mechanisms of Taste Transduction Bitter, Sweet, Umami • G-protein coupled receptor • Activates Phospholipase C • Increases messenger inositol triphosphate (IP3) • CA2+ Psychology 355

16. Taste Mechanisms of Taste Transduction Bitterness • Families of taste receptor genes - TIR and T2R Psychology 355

17. Taste Mechanisms of Taste Transduction Sweetness • Sweet tastants natural and artificial • Sweet receptors • T1R2+T1R3 • Expressed in different taste cells Psychology 355

18. Taste Mechanisms of Taste Transduction • Umami • Umami receptors: • Detect amino acids • T1R1+T1R3 Psychology 355

19. Taste Central Taste Pathways • Gustatory nucleus Point where taste axons bundle and synapse • Ventral posterior medial nucleus (VPM) of the thalamus • Primary gustatory cortex Receives axons from VPM taste neurons Psychology 355

20. Taste Psychology 355

21. Taste Psychology 355

22. Taste Central Taste Pathways (Cont’d) • Localized lesions • Ageusia- the loss of taste perception • Gustation • Important to the control of feeding and digestion • Hypothalamus • Basal telencephalon Psychology 355

23. Taste The Neural Coding of Taste • Labeled line hypothesis • Individual taste receptor cells for each stimuli • In reality, neurons broadly tuned • Population coding • Roughly labeled lines • Temperature • Textural features of food Psychology 355

24. Smell Pheromones • Smell— a mode of communication • Important signals • Reproductive behavior • Territorial boundaries • Identification • Aggression • Role of human pheromones Psychology 355

25. Smell The Organs of Smell Olfactory epithelium Olfactory receptor cells, supporting cells, and basal cells Psychology 355

26. Smell Psychology 355

27. Smell The Organs of Smell • Odorants: Activate transduction processes in neurons • Olfactory axons constitute olfactory nerve • Cribriform plate: A thin sheet of bone through which small clusters of axons penetrate, coursing to the olfactory bulb • Anosmia: Inability to smell • Humans: Weak smellers Due to small surface area of olfactory epithelium: Dogs have about 170 cm2 compared to 10 cm2 in humans, and about 100 times more receptors per unit area Psychology 355

28. Perception of Smell The dimensions of smell Psychology 355

29. Perception of Smell (cont.) • We can distinguish between about 10,000 different smellsDifferent threshold levels for different smells • Two thresholds for each smell -low threshold for the existence of a chemical, somewhat higher threshold to discriminate one smell from another Psychology 355

30. Perception of Smell • Adaptation - Olfactory fatigue - cross-adaptation • Smell Constancy - receptors are more stimulated during a deep sniff than a shallow one - the judgment of odor intensity does not change - Psychology 355

31. Smell Psychology 355

32. Pheromones: Mammals Powerful effects on behavior, specifically sexual behavior, territorial behavior and identification of kin Mammals • Most mammals only become sexually aroused in the presence of pheromones • Increased likelihood of pregnancy • Synchronization of estrus cycles • Mutual recognition of mother and offspring • Territory marking (e.g. dogs)

33. Pheromones: Mammals • Releasers - trigger a specific behavioral response • Primers - trigger a hormone response which increases the likelihood of certain types of behaviors Psychology 355

34. Pheromones: Humans Humans • infants can correctly identify their own mother's milk and are much more likely to nurse when its their own mother • female menstrual cycles can be altered by pheromones - the sorority effect • male and female behavior is highly influenced by pheromonest-shirt experiment - musky versus sweet - • the musky odor is rated by males and females as unpleasant and is thought to serve as a territorial marker among males

35. Pheromones: Humans Increase sexual arousal in males • Increases male perception of female attractiveness • women in photographs were rated as significantly more sexually attractive when judges were first exposed to alpha androstenol • Increases willingness of females to initiate social contact with males • females exposed to alpha androstenol were much more receptive to male-initiated contact • more likely to seek out male company • less likely to seek female company Psychology 355

36. Smell Olfactory Receptor Neurons • Olfactory Transduction Psychology 355

37. Smell Olfactory Receptor Neurons Olfactory Transduction Oderant to receptor protein Stimulates G(olf)-protein Activates adenylyl cyclase cAMP Opens Na+ Ca2+ channels Opens Cl- channels (out) Depolarization Psychology 355

38. Smell Olfactory Receptor Neurons Olfactory Transduction Psychology 355

39. Smell Olfactory Transduction Adaptation: Decreased response despite continuous stimulus Psychology 355

40. Smell Central Olfactory Pathways Psychology 355

41. Olfactory Bulb Olfactory bulb - organ which houses all the nerves which receive inputs from the olfactory receptors Limbic and Thalamic connections Olfactory cortex (frontal lobe)

42. Smell Central Olfactory Pathways Psychology 355

43. Smell Central Olfactory Pathways • Axons of the olfactory tract: Branch and enter the forebrain • Neocortex: Reached by a pathway that synapses in the medial dorsal nucleus Psychology 355

44. Smell Central Olfactory Pathways • Axons of the olfactory tract: Branch and enter the forebrain • Neocortex: Reached by a pathway that synapses in the medial dorsal nucleus Psychology 355

45. Smell • Spatial and Temporal Representations of Olfactory Information • Olfactory Population Coding • Olfactory Maps (sensory maps) • Temporal Coding in the Olfactory System Psychology 355

46. Concluding Remarks • Transduction mechanisms • Gustation and olfaction • Similar to the signaling systems used in every cell of the body • Common sensory principles - broadly tuned cells • Population coding • Sensory maps in brain • Timing of action potentials • May represent sensory information in ways not yet understood Psychology 355

47. End of Presentation Psychology 355