Olfaction

1. Olfaction

2. Objectives: Be able to • Define olfactory receptor proteins, glomeruli, and odotopes. • Describe odorant transduction. • Relate olfactory receptor proteins, receptor neurons, glomeruli, and odotopes to odor identification. • Describe theories of olfaction. • Describe the major parts of any perfume and explain their functions. • Discuss memory for odors.

3. Olfaction • Olfactory Physiology • From Chemicals to Smells • Olfactory Psychophysics, Identification, and Adaptation • Olfactory Hedonics • Olfaction, Memory, and Emotion

4. Olfactory Physiology • Odors: Olfactory sensations • Chemical compounds • But not every chemical is odorant • In order to be smelled: Molecule must be volatile, small, and hydrophobic

5. Odorants

6. Olfactory Physiology (cont’d) • The human olfactory apparatus: • Primary purpose of nose: to filter, warm, humidify air we breathe • Nose: Small ridges, olfactory cleft, olfactory epithelium

7. The Nose

8. The Olfactory System

9. Peripheral Olfactory System and the Olfactory Bulb

10. Olfactory Receptor Neurons

11. Olfactory Receptor Neuron

12. Olfactory Receptors on Cilia

13. Olfactory Receptor Proteins

14. (a) Two molecules with the same structure and different odor. (b) Two molecules with different structures but the same odor.

15. Olfactory Receptor Neuron Response to Two OdorsGray cells respond to odor 1, Dark outlined cells respond to odor 2, Two cells respond to both

16. Response of a Rabbit Glomerulus to Particular Odotopes

17. Olfactory Physiology (cont’d) • The olfactory epithelium: the “retina” of the nose: • Three types of cells: • 1. Supporting cells • 2. Basal cells • 3. Olfactory sensory neurons (OSNs)— have cilia protruding into mucus covering olfactory epithelium • Olfactory receptors (ORs): Interaction between these and odorant stimulates cascade of biochemical events

18. Olfactory Sensory Neuron

19. Olfactory Perception Pathway

20. Pathway for Odorant Molecule-Odorant Receptor Binding (1)

21. Pathway for Odorant Molecule-Odorant Receptor Binding (2)

22. Discussion Question 61 • Relate olfactory receptor proteins, receptor neurons, glomeruli, and odotopes to odor identification.

23. Olfactory Physiology (cont’d) • Olfactory loss can cause great suffering: • Sense of flavor (taste +) • Danger warning

24. Olfactory Physiology (cont’d) • Olfactory receptor cells are different from all other sensory receptor cells: They are not mediated by any protective barrier, make direct contact with brain. • (e.g., visual receptors are protected by cornea, receptors for hearing are protected by eardrum, taste buds are buried in papillae) • Therefore many drugs can be inhaled • OSN axons are among thinnest and slowest in body • Therefore it takes a long time to perceive odors compared to other perceptions

25. Olfactory Physiology (cont’d) • Subtle differences between sensation and perception: • Sensation occurs when scent is neurally registered • Perception occurs when becoming aware of detecting it

26. Olfactory Physiology (cont’d) • The genetic basis of olfactory receptors: • In 1991 Buck and Axel showed that genome contains about 1000 different olfactory receptor genes, each codes for single type of OR • Animals have fewer ORs • Trade-off between vision and olfaction

27. Olfactory Physiology (cont’d) • The feel of scent: • Odorants can stimulate somatosensory system through polymodal nociceptors (touch, pain, temperature receptors) • These sensations are mediated by the trigeminal nerve (cranial nerve V) • Often, it is impossible to distinguish between sensations traveling up cranial nerve I from olfactory receptors and those traveling up cranial nerve V from somatosensory receptors

28. From Chemicals to Smells • Theories of olfactory perception: • Shape-pattern theory: Match between shapes of odorants and odor receptors; dominant biochemical theory • Recent molecular research: Scents are detected by means of combinatorial codes • Vibration theory: There is a different vibrational frequency for every perceived smell, molecules that produce same vibrational frequencies will produce same smell

29. Presumed Odorant-Receptor Binding

30. From Chemicals to Smells (cont’d) • Specific anosmia: • The inability to smell one specific compound with otherwise normal smell perception • 50% of population has specific anosmia to androstenone • Change in detection can occur with training • This cannot be explained by vibration theory

31. From Chemicals to Smells (cont’d) • Study of stereoisomers: • Molecules that are mirror-image rotations of one another; although they contain the same atoms, they can smell completely different • Vibration theory cannot explain this phenomenon

32. Stereoisomers

33. From Chemicals to Smells (cont’d) • The importance of patterns: • How can we detect so many different scents if our genes only code for about 1000 olfactory receptors? • We can detect the pattern of activity across various receptor types • Intensity of odorant also changes which receptors will be activated • So weak concentrations of odorant do not smell the same as strong concentrations of it • Specific time order is important

34. Hypothetical Role of OR Receptor Activation

35. From Chemicals to Smells (cont’d) • Odor mixtures: • We rarely smell “pure odorants,” rather we smell mixtures • How do we process the components in an odorant mixtures • Two possibilities: • Analysis • Synthesis

36. From Chemicals to Smells (cont’d) • Analysis: Example from auditory mixtures: high note and low note • Synthesis: Example from color mixtures: mixing red and green lights, resulting in yellow light

37. Synthesis

38. National Geographic Smell Survey

39. Recognition Memory for Symbols, Faces, and Odors by Young and Elderly Persons

40. Hedonic Rating of Odorants

41. Making Perfume • Perfumes have three types of ingredients: • Essential oils (that give you the smell of the perfume), pure grain alcohol, water. • The mixture of essential oils includes three types: Bass notes – not volatile, stay longest on the skin • Middle notes – less volatile, influence smell for a pretty long time; they drag the bass notes into the air. • Top notes-most volatile, short lasting, drag middle notes

42. Perfume Oils • Last, but not least, here’s a list of the most easily found oils that may lead you to your dream perfume: • 1. Bass notes – sandalwood, vanilla, cinnamon, mosses, lichens, ferns; • 2. Middle notes – lemongrass, geranium, neroli, ylang-ylang; • 3. Top notes – orchid, rose, bergamot, lavender, lemon, lime.

43. Discussion Question 62 • Describe the major parts of any perfume and explain their functions

44. From Chemicals to Smells • Odor imagery: • Humans have little or no ability to conjure odor “images” • We do not think in smell, do not imagine smells

45. Olfactory Psychophysics, Identification, and Adaptation • Detection, discrimination, and recognition • How much stimulation is required before we perceive something to be there? • Olfactory detection thresholds: Depend on several factors

46. Olfactory Psychophysics, Identification, and Adaptation • Women: Generally lower thresholds than men, especially during ovulatory period of menstrual cycles, but their sensitivity is not heightened during pregnancy • Professionals can distinguish up to 100,000 odors (e.g., professional perfumers, wine tasters) • Durability: Our recognition of smells is durable even after several days, month, or year

47. Odor Recognition Retention

48. Olfactory Psychophysics, Identification, and Adaptation (cont’d) • Identification: • Attaching verbal label to smell is not easy • “Tip-of-the-nose phenomenon” • Compare to “tip-of-the-tongue” phenomenon • Anthropologists found that there are fewer words for experience of smells as opposed to other sensations

49. Olfactory Psychophysics, Identification, and Adaptation (cont’d) • Sense of smell and language: Disconnected, possibly because: • Olfactory information is not integrated in thalamus prior to processing in cortex • Majority of olfactory processing occurs in right side of brain while language processing occurs in left side of brain

50. Description of Colors vs. Odors