The Special Senses Chapter 17

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The Special Senses Chapter 17
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2011-02-20 20:32:41
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The Special Senses Chapter 17
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  1. About how many olfactory receptors do we have?
    We have 10-100 million olfactory receptors in our noses.
  2. Where are olfactory receptors located?
    • They are present in a specialized olfactory epithelium.
    • Olfactory epithelium covers the inferior surface of the cribiform plate. Extends along superior nasal concha.
  3. What cells are present in the olfactory epithelium?
    • Olfactory receptors
    • Supporting cells
    • Basal cells
  4. Function: Olfactory Receptors
    • - Bipolar neurons- the first order neurons of the olfactory pathway.
    • - Axon project through cribiform plate (at base of ethmoid bone) and ends at olfactory bulb.
    • - Olfactory haris are cilia that project from the dendrites and are stimulated by odorants (chemicals with smell).
    • - The odorant chemical produces a generator potential which initiated the olfactory response.

    *Part of the olfactory epithelium*
  5. Function: Supporting Cells
    • - Columnar epithelial cells in mucous membrane of nose.
    • - Provide nutrients, electrical insulation and support to the olfactory receptors.
    • - Provide a role in detoxification of chemicals.

    *Part of the olfactory epithelium*
  6. Function: Basal Cells
    • - Basal cells are stem cells- cells with a capacity to divide and differentiate.
    • - Basal cells replace the olfactory receptors that have a lifespan of only about a month.

    (This is unusual as mature neurons are usually not replaced)

    *Part of the olfactory epithelium*
  7. What is the purpose of Bowman's Glands?
    • Bowman's Glands = Olfactory Glands
    • Provide mucous to cover the surface of the olfactory epithelium.
    • Provide lubrication and helps dissolve some odorants.
    • Innervated by facial nerve VII - some chemicals cause stimulation of both nasal mucous glands and lacrimal glands. (Ex: pepper)
  8. Physiology of Olfaction
    • We can recognize about 10,000 different odors.
    • Odorants activate the enzyme adenylate cyclase. This results in a change of events that produces the messenger molecule cAMP, which in turn opens sodium channels resulting in membrane depolarization.
  9. Olfactory Transduction
    (Page 601 Figure 17.2)
    • 1. Odorant molecule binds to receptor
    • 2. Binding activates a G Protein that activates adenylate cyclase resulting in production of cAMP
    • 3. cAMP opens sodium ion channels
    • 4. Sodium ions enter resulting in a depolarization that may activate an action potential
    • 5. The action potential propagates along the axon of the olfactory receptors.
  10. What is meant by odor threshold and adaptation?
    • Olfactory sensation has a low threshold: Only a few molecules of certain substance need be present in air to be perceived as an odor. (Example: methyl mercaptan this is an odorant added to natural gas to make it smell)
    • Adaptation: Decreasing sensitivity to odors occurs rapidly. Olfactory receptors adapt by about 50% in the first second or so after stimulation but adapt very slowly thereafter.
  11. Whats the olfactory pathway?
    *Know the olfactory pathway from the olfactory receptors to higher brain centers*
    • Each side of the nose bundles of the slender, unmylinated axons of olfactory receptors extend through about 20 olfactory foramina in the cribriform plate of the ethmoid bone.
    • 40 or so bundles of axons collectively form the right and left olfactory nerve (I) that terminate in the brain in the olfactory bulbs.
    • Axons extend along olfactory tract to the limbic system and olfactory area of the frontal lobe.
  12. What different tastes can be detected?
    • Sour
    • Sweet
    • Bitter
    • Salty
    • Umami ("Meaty or Savory" by Japanese scientists, Stimulated by monosodium glutamate, MSG)

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