THE SENSE OF SMELL
Harry T. Lawless

1. Physiology and Anatomy
   Several million receptors, ciliated, at top of nasal passage.
   Axons from these cells converge on 2,000 or so glomeruli (amplification?)
   Spatial patterns of stimulation differ for different odors and patterns of lateral interaction are possible (sharpening?).

   Recent work by Buck and Axel suggests a large family of receptor proteins.

   Since volatile aromatics pass from the mouth to the nose, much ³taste² is really smell - RETRONASAL stimulation.

2. Humans can smell thousands of compounds in the MW range of 100 - 300.
   This leads to a wide variation in smell qualities.
   Different compounds have different potency - some have very low thresholds.

3. As in taste, adaptation, mixture inhibition and release effects occur.
   Adaptation - decrease in responsiveness under constant stimulation.
   Mixture inhibition - odors are less intense in mixtures (at equal concentration to their unmixed comparisons)
   Release from inhibition - when one odor in a mixture is adapted, the others may seem stronger.

4. A universal system for categorizing odors is lacking - several approaches
   Specific anosmia - smell blindness - may define categories
   Functional systems - wine aroma wheel; useful for odor naming
   Number of categories needed is probably LARGE (50 - 100?).

5. Olfaction is poorly connected to verbal processing
   - emotional tone and physical reaction are its functions.