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Chapter 8 The Chemical Senses

Chapter 8 The Chemical Senses. Introduction. Animals depend on the chemical senses to identify nourishment, poison, potential mate Chemical sensation Oldest and most common sensory system Chemical senses Gustation Olfaction Chemoreceptors.

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Chapter 8 The Chemical Senses

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  1. Chapter 8 The Chemical Senses

  2. Introduction Animals depend on the chemical senses to identify nourishment, poison, potential mate Chemical sensation Oldest and most common sensory system Chemical senses Gustation Olfaction Chemoreceptors

  3. in 1907 he conducted experiments to identify the fifth taste category…. umami

  4. Taste The Basics Tastes Saltiness, sourness, sweetness, bitterness, and umami Examples of correspondence between chemistry Sweet—sugars like fructose, sucrose, artificial sweeteners (saccharin and aspartame) Bitter—ions like K+ and Mg2+, quinine, and caffeine Advantage – Survival Poisonous substances - often bitter

  5. Taste The Basic Tastes Steps to distinguish the countless unique flavors of a food Each food activates a different combination of taste receptors Distinctive smell Other sensory modalities

  6. Taste The Organs of Taste Tongue, mouth, palate, pharynx, and epiglottis

  7. Taste The Organs of Taste Areas of sensitivity on the tongue Tip of the tongue Sweetness Back of the tongue Bitterness Sides of tongues Saltiness and sourness

  8. Taste The Organs of Tastes Papillae Foliate papillae Vallate papillae Fungiform papillae Threshold concentration Just enough exposure of single papilla to detect taste

  9. Taste Tastes Receptor Cells Apical ends Microvilli Taste pore Receptor potential: Voltage shift

  10. Taste Taste Receptor Cells

  11. Taste Mechanisms of Taste Transduction Transduction process Taste stimuli (tastants) Pass directly through ion channels Bind to and block ion channels Bind to G-protein-coupled receptors

  12. Taste Mechanisms of Taste Transduction Saltiness Salt-sensitive taste cells Special Na+ selective channel Blocked by the drug amiloride

  13. Taste Mechanisms of Taste Transduction Sourness Sourness- acidity – low pH Protons causative agents of acidity and sourness

  14. Taste Mechanisms of Taste Transduction Bitterness Families of taste receptor genes - TIR and T2R

  15. Taste Mechanisms of Taste Transduction Sweetness Sweet tastants natural and artificial Sweet receptors T1R2+T1R3 Expressed in different taste cells

  16. Taste Mechanisms of Taste Transduction Umami Umami receptors: Detect amino acids T1R1+T1R3

  17. Taste Central Taste Pathways

  18. Taste Central Taste Pathways (Cont’d) Localized lesions Ageusia- the loss of taste perception Gustation Important to the control of feeding and digestion Hypothalamus Basal telencephalon

  19. Taste The Neural Coding of Taste Labeled line hypothesis Individual taste receptor cells for each stimuli In reality, neurons broadly tuned Population coding Roughly labeled lines Temperature Textural features of food

  20. Smell Pheromones Smell— a mode of communication Important signals Reproductive behavior Territorial boundaries Identification Aggression Role of human pheromones

  21. Caspar Berthelsen Bartholin - Danish physician and theologian who who in 1619 wrote one of the most widely read Renaissance manuals of anatomy. He was first to describe the olfactory nerve (the first identified cranial nerve).

  22. Smell The Organs of Smell Olfactory epithelium Olfactory receptor cells, supporting cells, and basal cells

  23. Smell The Organs of Smell Odorants: Activate transduction processes in neurons Olfactory axons constitute olfactory nerve Cribriform plate: A thin sheet of bone through which small clusters of axons penetrate, coursing to the olfactory bulb Anosmia: Inability to smell Humans: Weak smellers Due to small surface area of olfactory epithelium

  24. Smell Olfactory Receptor Neurons Olfactory Transduction

  25. Smell Olfactory Receptor Neurons (Cont’d) Olfactory Transduction

  26. Olfactory Transduction Adaptation: Decreased response despite continuous stimulus Smell

  27. Central Olfactory Pathways (Cont’d) Smell

  28. Central Olfactory Pathways (Cont’d) Smell

  29. Central Olfactory Pathways (Cont’d) Axons of the olfactory tract: Branch and enter the forebrain Neocortex: Reached by a pathway that synapses in the medial dorsal nucleus Smell

  30. Spatial and Temporal Representations of Olfactory Information Olfactory Population Coding Olfactory Maps (sensory maps) Smell

  31. Concluding Remarks Transduction mechanisms Gustation and olfaction Similar to the signaling systems used in every cell of the body Common sensory principles - broadly tuned cells Population coding Sensory maps in brain Timing of action potentials May represent sensory information in ways not yet understood

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