Chemical Senses Chemical Senses Chemical Senses Senses of taste and smell are different from the other sensory systems Gustatory system (gustation) Taste system Olfactory system (olfaction) Smell system Why have these systems? Reproduction Survival Avoid danger Enjoyment (hedonics) 1
Olfactory Physiology Olfactory system is sensitive to airborne odorants Small (< 5.8 x 10-22g) Volatile (airborne) Hydrophobic (repels water) Olfactory Cleft Olfactory Epithelium Nasal Dominance Olfactory Physiology Within the olfactory epithelium Olfactory Sensory Neurons (OSNs) Olfactory cilia Olfactory receptor Supporting Cells Basal Cells OSMs are sensitive to specific odorants Olfactory Physiology OSN axons form the Olfactory Nerve Pass through the cribiform plate Anosmia result if damaged OSNs first synapse in Olfactory Bulbs Glomerulus input from specific OSNs 2
Olfactory Physiology Odor information then sent to Olfactory Cortex Piriform Cortex Amygdala-Hippocampal Complex Entorhinal Cortex Chemicals and Odors Shape-Pattern Theory Odor Perception Receptors and odorants have unique shapes that fit together Optimal odorant that will fit into each receptor Chemicals and Odors Vibration Theory of Odor Perception Odorants stimulate receptors similar to how sound waves stimulating auditory nerve fibers Atomic structure of different odorants have unique frequencies Similar odors will have similar chemical compositions...similar atomic frequencies similar smells 3
Chemicals and Odors Shape-Pattern vs. Vibration Theory Specific Anosmias Shape Pattern: Pro Vibration: Con Different Perception of Same Odorant Shape Pattern: Pro Vibration: Con Perception of Stereoisomers Shape Pattern: Pro Vibration: Con Olfactory psychophysics Detection vs. Discrimination vs. Recognition Staircase method is used for determining thresholds Triangle test is a method of assessing odor memory Identification Tip of the nose phenomenon Olfactory psychophysics Relationship between intensity and pleasantness is nonlinear and depends on initial liking 4
Olfactory Psychophysics Adaptation to odors can be short-term or long-term Receptor Adaptation occurs after odorants bind to receptors Cognitive Habituation occurs after very long exposure to an odorant Perceived Intensity Acetone Butane Textile Workers Non-Workers Olfactory Psychophysics Top down Influences on Odor intensity (Dalton, 1996) Expectations of what an odor is affect our sensitivity Sensitivity increases if we believe something is dangerous Perceived Intensity "Hazardous" "Healthful" Initial Exposure 20 Minutes Later Gustation Gustation serves a fundamental survival role by detecting nutritious vs. poisonous foods Retronasal Olfactory Sensations are the flavors from airborne molecules that stimulate the olfactory system Tastes Flavors Aromas 5
Physiology of Gustatory System Tastants are the dissolved chemicals on the tongue Taste Buds are imbedded in Papillae Filiform papillae Fungiform papillae Foliate papilae Circumvallate papillae Physiology of Gustatory System Taste Pore is an opening at the top of the taste bud Each bud contains 50-100 taste receptor cells (TCRs) Microvilli Salty TCRs Sour TCRs Sweet-bitter TCRs The Four Basic Tastes Salty is the perception of sodium (Na+) No transduction Affected by diet Sour is the perception of acids in foods Can indicate spoilage Preferences for sour differs between children and adults 6
The Four Basic Tastes Bitter can be the perception of poisons Genetic predispositions TAS2R gene family Hormone levels during pregnancy Sweet is the perception of sugars (CH2O) n Basic fuel for all cells Several types of sugars and sugar receptors, but we cannot distinguish The Four Basic Tastes Differences in perceived intensity of different compounds Detection threshold is lowest for bitter substances The Four Basic Tastes Taste Map does not actually exist 7
Genetics and Tasting In 1930 s researchers discovered bitter thresholds vary Phenylthiocarbamide (PTC) accidentally released in a lab Some could taste it, others could not Propylthiouracil (PROP) has a similar effect Nontasters (~25 % of population) Tasters (~60 % of population) Supertasters (~15 % of population) Genetics and Tasting Everyday Stimulation Most Intense Pain Cross-Modality Matching Psychophysical method Developed by S.S. Stevens Match intensity of a stimulus in one modality to intensity of stimuli in other modalities Loudest Sound Brightest Light Brightness of Sun Scalding Water Fire engine siren Severe Headache Airplane taking off Hi-beam headlights Skunk Cold Snow Low Beam Headlights Bacon Frying Mild Headache Brightness of Moon Whisper Sound of a Watch No Sensation Supertasters Tasters Nontasters Pleasures of Tastes Many taste preferences are innate Jacob Steiner s work with infant facial expressions Infants smile for salts and sugars Infants frown for bitter and highly sour substances 8
Pleasures of Tastes Chili Peppers (The best food on the planet) Scoville Units Associated Peppers 0-100 Bell Peppers 500-1,000 New Mexico 1,000-1,500 Espanola 1,000-2,000 Ancho & Pasilla 1,000-2,500 Cascabel & Cherry 2,500-5,000 Jalapeno & Mirasol 5,000-15,000 Serrano 15,000-30,000 de Arbol 30,000-50,000 Cayenne & Tabasco 50,000-100,000 Chiltepin 100,000-350,000 Scotch Bonnet & Thai 200,000-350,000 Hananero 577,000 Red Savina Habanero 16,000,000 Pure Capsaicin 9