Olfactive mucus

Future olfactive (olfactive mucus) detection systems will probably be ultrasensitive chemical sensors [16] detecting nucleotides and hormones (e.g., pheromones). Biosensor research may also become orientated towards new bioreceptors [265], and perhaps even new biocatalysts, such as artificial enzymes [266]. 

Scientific debate continues as to whether dogs detect odorants as vapors or whether they may be trapped and carried on particles inhaled. It has been shown with the aid of micron-sized graphite dust that inhaled particles are trapped by the hairs and mucus at the front of the nasal cavity, although a small fraction may pass through to the olfactory epithelium [12]. Accordingly, this would suggest that olfaction is primarily a vapor process, although particles may still play a role. 

The mechanism of olfaction has many theories but is not fully understood and is still the subject of research. The nose is the human organ that detects smell (Fig. 5.9). It extends from the face to the end of the palate. In its simplest explanation the two nasal cavities are lined with a mucous membrane, kept moist by the secreted substance mucus. Chemicals in the air entering the nose must dissolve in this mucus before they can be detected. A small area - about the size of a small postage stamp - in the upper part of the nasal cavity contains olfactory cells, which are sensitive to the chemicals in the mucus solution. For a molecule to be detected it must bind specifically to the sensitive cells that act as sensory receptors. The sensory receptors situated in the olfactory epithelium (epithelium is the name given to the outer layer of covering cells) are believed to bind specifically with substances according to the shape of their molecules. 

To these species the structure of air currents is not invisible. A considerable portion of their brains has evolved to process information from their whiskers (or vibrissae), and one may plausibly suggest that their olfactory sensitivity derives, at least in part, from the ability to monitor the structure of air and to situate a scent within the currents that eddy about their snouts (Cain, et al., 1985). If, even in the absence of vibrissae, human olfaction can, nevertheless, sense the heterogeneity of odors, this adds another complexity to our experience of smell. As argued above, diffusion through mucus limits the temporal resolution of olfaction to about 0.1 second. If humans have the capacity... 

The initial step in olfaction is the binding of an odorant to an odor binding protein (OBP). This step is essential since most odorants are hydrophobic in nature, and they could not otherwise pass through a polar mucus membrane to reach the olfactory receptors (OR). Thus, odor molecules are bound to the OBP and either simply solubilized by the OBP or perhaps actively transported to the OR by the OBP. Once at the OR, the odorant may be released to interact with the OR or the odorant-OBP complex is sensed by the OR — this has not been determined (Figure 1.5) [52]. The... 

The nasal passages function as passageways for air to enter the respiratory system and for olfaction. The air is warmed, humidified, and filtered as it passes through them. A mucus blanket, secreted by goblet cells, covers the nasal mucosa, which is heavily ciliated. The mucosa requires a balanced autonomic nervous system in order to function properly. The blood vessels, which function to warm the air, rely on the sympathetic nervous system to create the necessary amount of dilation. 

---