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  • OR : odorant receptor O : odorant BP : binding protein G olf : G protein GDP : guanosine diphosphate GTP : guanosine triphosphate AC : adenylate cyclase ATP : adenosine triphosphate cAMP : cyclic adenosine monophosphate CNGC : cyclic nucleotide-gated channel CaM : calmodulin; decreases CNGC sensitivity PDE : phosphodiesterase 5’AMP : 5’-adenosine monophosphate RK : receptor kinase PLC : phospholipase C ER : endoplasmic reticulum PIP 2 : phosphatidylinositol-4,5-bisphosphate IP 3 : inositol-1,4,5-trisphosphate PKC : protein kinase C; increases sensitivity of AC and CNGC There appears to be a 3rd pathway that utilizes a guanylyl cyclase (cGMP) receptor. Odorant cells are one of the few cells where [Cl - ] is greater inside than outside.  -arrestin binds the phosphorylated receptor AND appears to recruit phosphodiesterase to degrade the cAMP signal Kallmann syndrome, a rare hypogonadotropic hypogonadism
  • Olfaction

    1. 1. Olfaction The Sense of Smell
    2. 2. Smell helps us: <ul><li>Avoid dangerous situations (fumes, smoke) </li></ul><ul><li>Avoid consuming poisonous substances and spoiled food (sour milk) </li></ul><ul><li>Choose mates? </li></ul>
    3. 3. What are olfactory stimuli? <ul><li>Odorants (airborne molecules) </li></ul><ul><li>Odorants must be volatile (they give off vapors) </li></ul><ul><li>More vapors are given off when an odorant is heated!! (warm soup smells better than cold soup) </li></ul>
    4. 4. Olfaction Eric Niederhoffer SIU-SOM <ul><li>Olfaction signaling </li></ul><ul><li>Cyclic nucleotide gated channels </li></ul><ul><li>Inositol trisphosphate/Ca 2+ /Protein kinase C </li></ul>
    5. 5. Odorants reach olfactory receptors by: <ul><li>1. Being inhaled through the nose. </li></ul><ul><li>2. Through the mouth (vapors circulate up through throat) </li></ul>
    6. 6. Olfaction CNGC Cl - Ca 2+ PIP 2 Ca 2+ ER OR G olf   GDP PDE AC OR i RK O BP GTP GDP cAMP ATP  GTP 5’-AMP PLC OR G q GDP PKC RK GTP GDP GTP O BP CaM (IP 3 )
    7. 7. Olfactory Receptors Figure 16.3a, b
    8. 8. Olfactory Epithelium Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
    9. 9. Olfaction- originates in the nasal cavity
    10. 10. Olfactory system structures
    11. 11. Olfactory Receptor Neurons <ul><li>Carry impulses directly to the brain </li></ul><ul><li>Live for 5- 8 weeks & then die. </li></ul>
    12. 12. Summary: olfactory pathway <ul><li>Olfactory receptor neurons detect odorants in mucosa. </li></ul><ul><li>Signals are sent via olfactory receptor neurons to bulb structures (glomeruli). </li></ul><ul><li>Mitral and tufted cells carry signals to orbitofrontal cortex, temporal lobe, and the limbic system. </li></ul>
    13. 13. Which animal is most sensitive to smell? <ul><li>Dogs 300-10,000 times more sensitive to smell than humans </li></ul><ul><li>Why? Humans have 10-40 million olfactory receptor neurons, dogs have over a billion!! </li></ul>
    14. 14. Odor Hedonics <ul><li>What are “pleasant” and “unpleasant” odors? Variability is high. </li></ul><ul><li>Most universally-rated “pleasant” odorant is vanilla. </li></ul>
    15. 15. How is perception affected by odor? <ul><li>Odor enhances our experience of the world (food, surroundings, people). </li></ul><ul><li>We associate memories with certain odorants. </li></ul><ul><li>We lose the ability to experience “flavors” if our sense of smell is impaired. </li></ul>
    16. 16. Anosmia : loss of sense of smell <ul><li>May be to specific odors or all odors. </li></ul><ul><li>Caused by infection to nasal cavity or brain injury (frontal lobe). </li></ul><ul><li>About 2 million people in US are anosmic. </li></ul>
    17. 17. Olfaction and behavior <ul><li>A. Infant perception & attachment </li></ul><ul><li>Babies enthusiastically “orient” to pleasant odors (banana, vanilla) and cry/grimace to unpleasant odors (shrimp; rotten eggs). </li></ul><ul><li>Babies can discriminate their mother’s scent from other women (Macfarlane, 1975). </li></ul>
    18. 18. Chemical Senses – Taste and Smell Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings <ul><li>Both senses use chemoreceptors </li></ul><ul><ul><li>Stimulated by chemicals (odorants) in solution </li></ul></ul><ul><ul><li>Taste has four types of receptors </li></ul></ul><ul><ul><li>Smell can differentiate a large range of chemicals </li></ul></ul><ul><li>Both senses complement each other and respond to many of the same stimuli </li></ul>
    19. 19. Olfaction – The Sense of Smell Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings <ul><li>Olfactory receptors are in the roof of the nasal cavity </li></ul><ul><ul><li>Neurons with long cilia </li></ul></ul><ul><ul><li>Chemicals must be dissolved in mucus for detection يكتشف </li></ul></ul><ul><li>Impulses are transmitted via the olfactory nerve </li></ul><ul><li>Interpretation تفسير of smells is made in the cortex </li></ul>
    20. 20. Smell (Olfaction) <ul><li>Receptors are part of the olfactory epithelium </li></ul><ul><li>Olfactory epithelium composed of: </li></ul><ul><ul><li>Cell bodies of olfactory receptor cells </li></ul></ul><ul><ul><li>Supporting cells – columnar cells </li></ul></ul><ul><ul><li>Basal cells – form new olfactory receptor cells </li></ul></ul>
    21. 21. Smell (Olfaction) <ul><li>Olfactory receptors react to their stimuli by developing a generator potential (depolarization) that triggers يثير one or more nerve impulses. </li></ul><ul><li>Olfaction has a low threshold. </li></ul><ul><li>Adaptation occurs rapidly. </li></ul>
    22. 22. The olfactory pathway <ul><li>Olfactory (I) nerves (bundles of olfactory axons) run on both sides of the nose. </li></ul><ul><li>Terminate ينتهي in the brain in paired masses of grey matter (olfactory bulbs). </li></ul><ul><li>Within the olfactory bulbs the axon terminals of the olfactory receptors (1 st order neurons) form synapses with dendrites & cell bodies of second order olfactory neurons. </li></ul><ul><li>Axons of the olfactory bulb neurons extend posteriorly and form the olfactory tract. </li></ul>
    23. 23. <ul><li>Axons of the olfactory tract project تروح to the primary olfactory area. </li></ul><ul><li>Other axons of the olfactory tracts extend to the limbic system and hypothalamus (emotional responses to odors). </li></ul><ul><li>Axons extend from the primary olfactory area to frontal lobe (odor عطر .. او رآآئحه identification & discrimination). </li></ul>The olfactory pathway
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