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taste & smell

DENT/OBHS 131 Neuroscience. taste & smell. 2009. Learning Objectives. Describe the cranial nerve / brainstem sensory innervation of the taste buds / tongue Explain the general ionic mechanism of taste cell excitation Identify the cortical regions important for primary gustation

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taste & smell

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  1. DENT/OBHS 131Neuroscience taste & smell 2009

  2. Learning Objectives • Describe the cranial nerve / brainstem sensory innervation of the taste buds / tongue • Explain the general ionic mechanism of taste cell excitation • Identify the cortical regions important for primary gustation • Compare and contrast olfaction with other sensory modalities, including its cranial nerve and nature of projection to cortex • Discuss how sub-modalities of taste and smell are sorted as they ascend to the cortex • Appreciate that taste / smell and other sensory modalities are combined at the level of the cortex along with limbic information to produce full sensation of flavor

  3. 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

  4. Significance • Emotion and memory: limbic system

  5. Perception of flavor • The chemical senses act in concert • Multiple components: • Taste buds • Olfactory receptors • Free-nerve endings (CN V) • e.g. spiciness & temperature • Emotional and cognitive valence

  6. Taste

  7. Blue tongue disease

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

  9. Papillae, buds & cells • circumvallate

  10. Learning Objective #1 • Describe the cranial nerve / brainstem sensory innervation of the taste buds / tongue

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

  12. Rostral medulla • Why are we here?

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

  14. Learning Objective #2 • Explain the general ionic mechanism of taste cell excitation

  15. 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

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

  17. 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 (to other regions) • Parabrachial nucleus (non-human)

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

  19. Learning Objectives #3 & 4 • Identify the cortical regions important for primary gustation • Discuss how sub-modalities of taste and smell are sorted as they ascend to the cortex

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

  21. Neural coding of taste

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

  23. Teaching Objective #5 • Compare and contrast olfaction with other sensory modalities, including its cranial nerve and nature of projection to cortex

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

  25. Olfactory receptor neurons

  26. Epithelia - surface area

  27. Olfactory transduction • very fine unmyelinated axons

  28. Learning Objective #5 • Discuss how sub-modalities of taste and smell are sorted as they ascend to the cortex

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

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

  31. Learning Objective #6 • Appreciate that taste / smell and other sensory modalities are combined at the level of the cortex along with limbic information to produce full sensation of flavor

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

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

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