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  1. The chemical sense: taste and smell
    • Our sense of taste (gustation) and smell
    • (olfaction) complement each other
    • Both rely on chemoreceptors, cells with membrane
    • bound proteins which bind to specific chemicals
    • Taste receptors respond to chemicals dissolved
    • in saliva
    • Olfaction responds to chemicals dissolved in
    • mucus coating the nasal membranes&
  2. Smell (olfaction)
    • 80% of taste is smell
    • When nasal receptors are blocked, food tastes
    • bland
    • The olfactory epithelium is localized to a 5cm2
    • patch on the roof the nasal cavity (superior nasal conchae)Sniffing draws more air over the olfactory
    • epithelium
    • Recent research indicates that humans can use
    • bilateral differences in smell to track an odor trail
  3. The nasal epithelium contains 3 cell types
    • Basal cells are stem cells which replace
    • olfactory neurons every 30 days or so
    • Supporting cells, containing a yell brown
    • pigment dominate the epithelium
    • Olfactory (bowman’s) glands secrete thick mucus
  4. Smell (olfaction)
    • The olfactory receptors are highly modified
    • neurons, each with up to 20 cilia which extend into the mucus
    • Each olfactory receptor neuron expresses 1 of
    • 347 odor receptor genes.
    • Odor receptor proteins on the neurons respond to
    • airborne molecules (odorants) that are dissolved in the mucus
    • The odor receptor truggers the G protein signal
    • pathway
    • A secondary messenger, cyclic AMP, opens Na+
    • (and Ca2+) channels
    • This leads to depolarization of the membrane of
    • the neuron
    • If depolarization is sufficient, an AP ( or
    • train of Aps) is generated
Card Set
AP 1
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