Trigeminal chemoreception

Trigeminal chemoreception mediates the perception of chemical pain, as well as thermal, tactile, and proprioceptive cues (Green et al. 1990). This review is limited to the discussion of chemical pain, the kind of stimulation that humans describe as burning, itching, or tingling (Rozin et al. 1982). Trigeminal nociceptors are free nerve endings that can be found in the mouth and nose, as well as 

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Mason, J. R., Greenspon, J. M. and Silver, W. L. (1987a). Capsaicin and its effects on olfaction and trigeminal chemoreception. Acta Physiologica Hungarica 69,469-479. 

Mason, J.R. L. Clark. 1996. Capsaicin detection in trained European starlings the importance of olfaction and trigeminal chemoreception. Wilson Bull. 107 165-169. 

Vertebrates possess three primary chemosensory systems gustation ( taste ), trigeminal, and olfaction ( smell ) but only one of these, the olfactory system, mediates responses to pheromones. Chemicals that stimulate the olfactory system are known as odorants and comprise one type of biological cue (any entity that stimulates a sensory system). Bouquets of odorants that can be discriminated as specific entities are termed odors. The olfactory system contains olfactory receptor neurons (ORNs) that comprise cranial nerve I and project directly to the forebrain. ORNs are now known to express only one to a few olfactory receptor proteins ( receptors ), which means that the chemoreceptive range of each neuron can be very narrow. The olfactory system also has several subcomponents including the vomeronasal organ, which is described below. 

It irritates skin and mucous membranes. In terms of chemoreception, it irritates the trigeminal nerve. Capsaicin binds to the vanilloid receptor subtype 1 (VRl). Birds lack this receptor. Since they cannot sense capsaicin, they eat and distribute seeds of red hot peppers. Medically capsaicin is used as painkiller (analgesic). 

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