2. CHEMICAL SENSES Olfaction – Receptors – Olfactory Pathway Taste – Basic qualities – Receptors – Taste Pathway – Supertasters

3. Chemical Senses Smell and taste detect chemicals that come into contact with receptors Chemical senses act as “gatekeepers,” determining which things the body should consume

4. Olfactory Receptors Chemicals stimulate cilia on olfactory sensory neurons Located in olfactory mucosa Cilia contain olfactory receptors Receptors replaced every 5-7 weeks

5. Olfactory Receptors About 350 types of receptors (in humans) Odorants cause different patterns of responses across receptors (recognition profiles) Combinatorial code

6. Olfactory Pathway Trigeminal Nerve carries information from olfactory receptors Olfactory bulb: contains glomeruli where OSN fibers have synapses Amygdala (limbic system)

7. Olfactory Pathway Primary Olfactory Cortex (Piriform) - under temporal lobes Secondary Olfactory Cortex (Orbitofrontal) - frontal lobes near eyes

8. Taste: Basic Qualities sweet - sugar hydroxyl sour - hydrogen ions salty - sodium ions bitter - bases umami (savory) - MSG

9. Taste Receptors papillae contain taste buds taste buds contain taste cells tips of taste cells are taste pores receptor sites are located on the taste pores

10. Taste Receptors areas on the tongue are sensitive to all 5 qualities, but areas differ in sensitivity center of the tongue has no taste receptors taste receptors are also located in the mouth and throat receptors replaced every 10 days

11. Taste Pathway Chorda Tympani Nerve: front and sides of tongue Glossopharyngeal Nerve: back of tongue Vagus Nerve: mouth and throat

12. Taste Pathway Nucleus of the Solitary Tract (NST) in brain stem thalamus frontal lobes: – Insula – Frontal operculum cortex – Orbitofrontal cortex (bimodal taste/smell neurons)

13. Supertasters Sensitivity to the bitter taste of PROP is genetically based Supertasters are especially sensitive Higher density of taste buds Lower threshold for bitterness Differences in types of taste receptors