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raincali
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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&
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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
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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
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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
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