The
chemical senses, particularly olfaction, are deemed the oldest sensory system.
These sensory systems are dedicated to the detection of chemicals in the environment.
Here I will briefly describe olfactory system based on our present understanding
of olfactory system, however, in many ways, it is the least understood of the
sensory modalities. I will briefly describe vomeronasal system first; but then
focus on olfactory system for the rest of the discussion.
The Vomeronasal System:
This system is found in some vertebrates. The receptors of this system is found in the roof of mouth, and fibers from the receptors project to the accessory olfactory bulb. Vomeronasal system is specialized for the recognition of sex-pheromones/ territory odors, aggression, suckling behavior; however, vomeronasal system is nonfunctional in adult human beings.
The Olfactory System:
The olfactory system detects airborne molecules called odors. In humans, odors provide information about food, other people, animal, and many other aspects of the environment. Human beings can smell various acids, alcohol, aldehydes, ester, aromatic compounds, as well as other compounds and mixtures. From an evolutionary perspective, olfactory system seem to play an important role in the survival of different species; for example, in mouse, 2% of its entire genome encodes genes for olfactory receptors. In fact, it is the largest GPCR (G-protein coupled reactions) family by far. As a result a lot of researches are being conducted on olfactory system now, still many aspects of olfactory system remains unknown.
Acknowledgments: I am grateful to Professor Carl Hopkins (Cornell University) as some figures and discussion materials are taken from his lectures on olfactory system. Photo Courtesy: www.art-et-parfum.com/ creation.htm
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