Olfactory chemoreceptor system

Apart from taste, vertebrates have five different chemoreceptor systems for airborne chemosignals the main olfactory system, the vomeronasal organ (VNO), the trigeminal nerve, the septal organ of Masera, and the nervus termi-nalis. They each will be discussed in turn. All five are fully functional in most mammals (Fig. 5.1). 

Margolis, F.L. (1980) A marker protein for the olfactory chemoreceptor neuron. In R.A. Bradshaw and Schneider (Eds.), Proteins of the Nervous System, pp.59-84. Raven Press, New York. 

Mammalian semiochemistry (Albone, 1984) differs from the analogous study of insects, in which chemistry has played a prominent role, in that mammalian systems are characterized by a greater complexity. Unlike insect chemoreceptors, mammalian olfactory chemoreceptors are not tuned to specific compounds but detect a wide range of substances and odors (which may be associated with quite complex mixtures of compounds) that will be differentiated at a higher level in the nervous system (Shirley, 1984). 

The vomeronasal system, also known as the accessory olfactory system, consists of chemoreceptors, organized into the VNO, the vomeronasal nerve, its terminal, the accessory olfactory bulb, and more central pathways. First described by Jacobson in 1811, the VNO has been studied intensely. We now know how stimuli reach it and what behaviors it mediates. The VNO occurs in amphibians, reptiles, and mammals. Among mammals, it is best developed in marsupials and monotremes. In birds it only appears during embryogenesis. The VNO and its function are best known for squamate reptiles, particularly snakes, and rodents and ungulates among the mammals. 

Chemoreceptor Gene Families in the Main Olfactory System... 

The elicitation of neural responses caused by odorants is not restricted to the olfactory systems other excitable systems, e.g., the trigeminal, vomeronasal, and contact chemoreceptor, are also able to respond to odorants. From these facts, it may be considered that an excitable membrane in general might respond to odorants. 

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