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taste & smell

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

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taste & smell

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

  12. Taste transduction • Specific chemical interaction • microvillae • G-protein receptor • Ion channel • Depolarization • Passive spread is enough • …but can produce APs • Ca2+ 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 • Primary gustatory cortex • Insular / frontal operculum • Rostral medulla • reflexes, e.g. DMN X • VPM (head - sensory) • Cortical relay • via central tegmental tract (ipsi) • Rostral pons • Parabrachial nucleus (non-human)

  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 smell selectivity & integration memory & emotion dorsomedial nucleus

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

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