The Olfactory System Smell

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Olfactory System notes for Human Anatomy Class

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The Olfactory System Smell

  1. 1. The Olfactory System - Smell
  2. 2. Why is smell important? <ul><li>Strongly associated with memories </li></ul><ul><li>Key factor in tasting food. </li></ul>
  3. 3. Human experiment: How well do we taste without smell?
  4. 4. The olfactory epithelium: the “retina” of the nose: <ul><li>– Three types of cells: 1. Supporting cells 2. Basal cells 3. Olfactory sensory neurons (OSNs)—cilia protruding into mucus covering olfactory epithelium </li></ul><ul><li>– Olfactory receptors (ORs): Interaction between these and odorant stimuli </li></ul><ul><li>5 cm ^2 – covered with mucus </li></ul><ul><li>60 day life span before replacement </li></ul>
  5. 5. Hey gang, Please ignore the religious parts… sorry, there aren’t many smell videos out there : ) Please stop at 9:05
  6. 6. Unique… <ul><li>Olfactory receptor cells are different from all other sensory receptor cells: They are not mediated by any protective barrier, make direct contact with brain. – (e.g., visual receptors are protected by cornea, receptors for hearing are protected by eardrum, taste buds are buried in papillae) – Therefore many drugs can be inhaled – OSN axons are among thinnest and slowest in body – Therefore it takes a long time to perceive odors compared to other perceptions </li></ul>
  7. 7. 2 parts to Olfactory system <ul><li>Main Olfactory System </li></ul><ul><ul><li>Odor Detection </li></ul></ul><ul><ul><li>Odor Coding </li></ul></ul><ul><li>Accessory Olfactory System </li></ul><ul><ul><li>Pheromone Detection </li></ul></ul><ul><ul><li>Pheromone Coding </li></ul></ul>
  8. 8. In the Nose: <ul><li>Neurons express one receptor </li></ul><ul><li>Neurons with the same receptor are in random locations </li></ul><ul><li>Neurons with the same receptor send axons to the same place </li></ul><ul><li>Neurons with same receptor send axons to one glomerulus </li></ul><ul><li>Neurons with different receptors project to different glomeruli </li></ul>
  9. 9. 1: Olfactory bulb 2: Mitral cells 3: Bone 4: Nasal epithelium 5: Glomerulus 6: Olfactory receptor cells
  10. 10. <ul><li>- Each glomerulus receives input from one receptor type </li></ul><ul><li>- About 1000 different types of receptor cells </li></ul><ul><li>- Combinations result in tens of thousands of unique odors </li></ul>
  11. 11. The Second Nose: the Vomeronasal organ <ul><li>detects pheromones (chemical cues secreted by animals) </li></ul><ul><li>- best evidence of pheromones in insects and many mammals ( this is one of the reasons teenagers have BO…body is producing sex hormones to stimulate puberty) </li></ul><ul><li>triggers stereotyped behaviors (mating and fighting) maybe if high schoolers wore more deodorant we would have less fights  </li></ul>
  12. 13. Smell Pathway <ul><li>1.Scent molecules enter the nose. </li></ul><ul><li>2.Molecules attach to knob, that projects from the epithelial cell through mucus layer of the nasal mucosa. </li></ul><ul><li>3. 8-20 cilia extend from the know head with their lower ends an axon connecting to the olfactory bulb. </li></ul><ul><li>4. Axons join to form Olfactory tract </li></ul><ul><li>5.Nerve impulse travels to the thalamus and then the frontal cortex to compare with memories until recognition is reached. </li></ul><ul><li>6. Recognition activates impulses – flight, reflex, digestive etc. </li></ul>

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