Trigeminal system

Tucker D. (1971). Non-olfactory responses from nasal cavity Jacobson s Organ and trigeminal system. In Handbook of Sensory Physiology Chemical Senses, 1. Olfaction (Biedler L., ed.). Springer, Berlin, pp. 151-181. 

Bouvet, J. F., Godinot, F., Delaleu, J. C., and Holley, A. (1989). Interaction between the olfactory and the trigeminal systems in the frog. Chemical Senses 14,200. 

Non-olfactoiy responses from the nasal cavity Jacobson s organ and the trigeminal system. In Handiook of Sensory Physiology, vol. 4, ed. L. M. Beidler, pp. 151-181. Berlin Springer-Verlag. 

Many airborne substances are complex stimuli. They are combinations of many chemicals which can interact at one or several levels before or during the perception chemical or physical interaction in the gas mixture, interaction of molecules at the receptor surfaces (olfactory and trigeminal systems), peripheral interaction in the nervous system and finally interaction in the central nervous system. Therefore, effects such as masking, neutralisation and counteraction are not surprising in gas mixtures [13]. 

Odour only exists in the higher brain and is a synthesis of signals from the olfactory pathway, those of the trigeminal system, those from other senses (e.g. taste) and so on. There are many gates along the pathway with the potential to shut off or enhance odour signals. All of the various nerve pathways (those due to different smells and those from other channels interact with each other and so we can have odour enhancement or suppression as a result of these various interactions. For instance, any... 

Certain neurophysiological experiments in the tortoise and the rabbit implied that the trigeminal system behaved unlike the olfactory system in certain important temporal properties (7 ). 

Odors are perceived via the olfactory system, which is composed of two organs in the nose the olfactory epithelium, a very small area in the nasal system, and the trigeminal nerve endings, which are much more widely distributed in the nasal cavity (11). The olfactory epithelium is extremely sensitive, and humans often sniff to bring more odorant in contact with this area. The trigeminal nerves initiate protective reflexes, such as sneezing or interruption of irrhalation, with exposure to noxious odorants. 

TK NKxr displays a broad distribution in both peripheral tissues and in the central nervous system (CNS). In both CNS and enteric neurons, NKxr stimulation increase their excitability, whereas in trigeminal ganglion neurons SP has no intrinsic electrophysio-logical effects but is capable to enhance the amplitude of the inward current induced by the stimulation of serotonin 5-HT3 recqrtors. This enhancement dqjends on the activation of PKC via the stimulation of NKX recqrtors. This is an interesting case of receptor cross talk. Other functions of NKxr have been also highlighted. 

Absence from the first developmental stages as in whales and some Old World monkeys suggests that functional substitution is provided by other nasal chemoreceptors. The ganglia and fibres of the terminal nerve system (N. terminalis, Fig. 2.9) are the principal candidate (Wirsig and Leonard, 1987). The role of the trigeminal input, although a minor sensor, could well be expanded in a limited capacity (Tucker, 1971 Wysocki and Meredith, 1987 Westhofen, 1987). 

Devitsina G.V. and Cherova L. (1992). The trigeminal nerve system and its interaction with olfactory and taste system in fishes. In Chemical Signals in Vertebrates 6 (Doty R.L. and Miiller-Schwarze D., eds.). Plenum, New York, pp. 85-88. 

KuUe, T. J., and G. P. Cooper. Effects of formaldehyde and ozone on tlie trigeminal nasal sensory system. Arch. Environ. Health 30 237-243, 1975. 

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). 

An interaction between main olfaction and the trigeminal somatosensory system has been proposed to facilitate directional smelling. For carbon dioxide and menthol, human subjects were able to tell the odor direction in 96% of cases, while the results for hydrogen sulfide and vanillin were random (Kobal et ah, 1989). Rats can discriminate odor direction in one sniff (Rajan et ah, 2006). 

Jakubas, W. J. and Mason, J. R. (1991). Role of avian trigeminal sensory system in detecting coniferyl benzoate, a plant allelochemical. Journal of Chemical Ecology 17, 2213-2221. 

HT3 receptors are located exclusively on neurons and are widely distributed throughout the peripheral and central nervous systems. In the periphery, 5-HT3 receptors are found on autonomic, sensory, and enteric neurons (Fozard 1984). In the central nervous system, 5-HT3 receptors are labeled in cortex, hippocampus, caudate hypothalamus, brain stem, midbrain, and cerebellum, with the highest density in discrete nuclei of the lower brain stem (e.g., dorsal vagal complex and spinal trigeminal nucleus), the area postrema, and substantia gelatinosa at all levels of the spinal cord (Palacios et al. 1991 Waeber et al. 1989). 

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