Biological Olfaction - The Electronic Nose Artificial Olfaction Technology - page 73

Fig. 3.9 Odorants pathway

3.3.5 Olfactory Epithelium

The sense of smell begins with an odorant molecule binding to a receptor on the
cilia of olfactory receptor neurons in the olfactory epithelium.

1. The olfactory epithelium resides in the back of the nasal cavity below the
olfactory bulbs.
2. Roughly 5-10 million olfactory receptor neurons (ORNs) reside in the olfac-
tory epithelium. These receptors are true bipolar neurons, extending a dendrite
toward the epithelial surface and an axon that project into the olfactory bulb.
The ends of the ORN dendrites are knobs that contain fine cilia projecting into a
layer of mucus. On these cilia the odorant receptors are located. Odorants are
dissolved in the mucus layer and bind to the receptors, initiating the trans-
duction process that leads to an action potential in the ORN.

Humans and other mammals are capable of discriminating a great variety of
odors and flavors. The olfactory capability of humans is somewhat limited com-
pared with that of some other mammals; we are nevertheless able to perceive
thousands of different odorous molecules (odorants). Perfumers, who are highly
trained to discriminate odorants, say that they can distinguish as many as 5,000
different types of odorants, and wine tasters report that they can distinguish more
than 100 different components of taste based on combinations of flavor and aroma.

3.4 Olfactory Transduction

The information about conditions inside or outside the body is provided to the
central nervous system with the cell processes (i.e., Sensory receptors). Our sen-
sitivity to temperature, pain, touch, pressure, vibration is described as generally