1. taste & smell Basic Neuroscience NBL 120 (2008)

2. Gustatory & olfactory systems Extract information from chemicals in the environment G-protein coupled receptors Taste: (+ ion channels) Taste and olfactory receptor cells undergo continual lifetime turnover Taste: modified epithelial cells Smell: neurons Stimulus information is encoded in populations of neurons

3. Significance Emotion and memory: limbic system

4. Perception of flavor The chemical senses Multiple components: Taste buds Olfactory receptors Free-nerve endings (CN V) xe.g. spiciness & temperature Emotional and cognitive valence

5. Taste

6. Blue tongue disease

7. Taste buds Lingual buds: Foliate Fungiform Circumvallate 2000-5000 buds 50-150 taste cells

8. Papillae, buds & cells circumvallate

9. Innervation Chorda tympani (VII) Taste map - myth? palate & pharynx

10. Rostral medulla Why are we here?

11. VII IX X CNs and solitary nucleus/tract Principal visceral sensory relay Rostral portion

12. Taste transduction Specific chemical interaction microvillae G-protein receptor Ion channel Depolarization Passive spread is enough …but can produce APs Ca 2+ entry Transmitter (glutamate) release

13. G-proteins & ion channels Sweet Salty Sour Bitter “Umami” TRP channels (see PAIN) Tim Jacob (Cardiff University, UK)

14. Anatomical path Rostral medulla reflexes, e.g. DMN X VPM (head - sensory) Cortical relay via central tegmental tract (ipsi) Rostral pons Parabrachial nucleus (non-human) Primary gustatory cortex Insular / frontal operculum

15. Cortical processing orbitofrontal cortex integration, e.g., olfactory information Projections amygdala hypothalamus striatum

16. Broad tuning of taste pathway Solitarius cell - multiple Orbital cortex cell - selective

17. Neural coding of taste

18. Olfaction My dog’s got no nose…. How does it smell? Awful

19. Anatomical points Olfactory receptor cells are real neurons CN I & bulb is really part of the CNS No thalamic relay

20. Olfactory receptor neurons

21. Epithelia - surface area

22. Olfactory transduction very fine unmyelinated axons

23. Glomeruli - olfactory bulb Convergence (1000’s) & sorting mitral cells

24. CNS pathways Anterior olfactory nucleus Inhibit contralateral bulb Olfactory tubercule Primary olfactory cortex Piriform cortex Periamydaloid cortex (part of) parahippocampal gyrus Further projections Limbic system - amygdala Thalamus

25. Thalamic relay dorsomedial nucleus smell selectivity & integration memory & emotion

26. damage Anosmia Taste loss? Parkinson’s disease Seizures (uncinate) Begin with smell or taste (unpleasant)