Functions chemoreception

Analysis of the relative distribution and expression of OR/VNOR genes would clarify the variety of functional chemoreceptive divisions amongst this transitional group. 

The higher vertebrates retained the basic Nervus termitialis, a VN-associated chemoreceptive neurai network (Fig. 2.9) with some cognate functions (Chap. 5 and Murphy, 1998). In mammals, an apparently unique and enigmatic OR cell cluster with a separable MOB input occurs. This minor structure (Fig. 2.10), the Septal Organ (of Masera), is possibly adaptive, has no peripheral connection to the VNO, and its capacity for central modulation of MOS and or AOS input is unknown (Naguro, 1984 Marshall, 1986). 

Evans C.S. (1984). On the structure and function of accessory chemoreceptive organs. Acta Zool Fennica 171, 57-62. 

Graves B.M. (1993). Chemical delivery to the vomeronasal organs and functional domain of Squamate chemoreception. Brain Behav Evol 41, 198-202. 

Evolution of metazoan chemoreception eventually gave rise to anatomically and functionally distinct chemosensory systems—olfac-... 

Temperature may significantly affect chemoreception. For instance, electrical responses to amylacetate delivered to olfactoiy receptors of a tortoise, Gopherus polyphemus, were little affected by air temperatures between 20 and 30 °C at the nares but changed considerably above and below that range. Up to - -35 °C and down to -1-10 °C, the olfactory response was a monotonic slowly decreasing function of temperature (Tucker, 1963 see also Grundvig etal., 1967). 

In general, perceived odor intensity is a power function of the odor concentration. The exponent is below 1, meaning that boosting the perceived intensity requires increasingly more odor production. As odor production becomes more and more costly, fine-tuning of chemoreception (instead of odor production) becomes the more attractive alternative evolutionarily. 

Thus, in various insect species, the expression of CSP occurs in many different tissues, especially in the legs and contact sensory organs. The differences between CSPs and OBPs in tissue distribution and developmental expression suggest that the roles of these proteins in chemoreception may also be different. CSPs may have a broader function than OBPs, functioning in more systems than olfaction and taste, perhaps as general molecule carriers but especially involved in the transport of contact sensory molecules. 

Dimensionless numbers are very simple to calculate, although proper interpretation is dependent on the choice of variables such as which length to use for the characteristic length. The magnitudes of the dimensionless numbers are predictors of physical behavior. In addition, the functional relationships written in terms of the appropriate dimensionless numbers are extremely powerful because they will be valid for that geometry and boundary conditions for a wide range of variable combinations. In chemoreception there are six dimensionless numbers that are particularly important (Re, Pe, Sh, Fo, Sc, and Wo). 

Non-ciliated receptors show much variation. Some resemble ciliated receptors in that they have a terminal dendritic bulb with a basal body but no distal cilium (85, 942). Others, as in H. nana (Fig. 2.9), show little structural specialisation and appear to be little more than free nerve endings which may have a single, double or triple structure. Endings which do not penetrate the tegument to the external environment may have a mechanoreceptive or proprioceptive (i.e. receptive to internal stimuli) -rather than chemoreceptive - function (12, 206, 942). 

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