Initial mechanisms basic to olfactory perception.

Animal experimentation has proposed three mechanisms at the olfactory mucosa that may underlie olfactory discrimination. First, the olfactory receptor cells appear selectively tuned to different odorants. Second, in a gas chromatographic-like process, the molecules of different odorants appear to be distributed in different sorption patterns across the mucosal surface. Third, different regions of the mucosa appear to have different selective sensitivities. These three mechanisms could complement each other by together generating a greater number of neural discharge patterns to encode the odorants passing over the mucosal surface. In this interplay, the mucosal distribution patterns could differentially limit the receptor cells and mucosal regions to which different odorants have access. The mucosal distribution pattern could thereby affect the odorant analyses made by these other mechanisms as well as contribute its own analysis. The mucosal distribution patterns appear fairly stable in the face of rather wide variations in the pertinent variables characterizing the nasal airflow (namely, odorant concentration, flow rate, volume, and duration). There are, however, limits to these variables beyond which significant shifts in the molecular distributions and neural discharge patterns can be produced. Thus, in humans any naturally occurring or surgically induced alteration in the nasal airflow which appreciably alters these variables may affect olfactory perception. Olfaction in a laryngectomized patient is discussed as an example.