Kemoreception

Kemoreception, often spelled chemoreception, is the physiological process by which organisms detect chemical stimuli in their environment or body. It encompasses the sense of smell (olfaction), taste (gustation), and other chemically mediated cues that influence behavior and physiology. In many species, kemoreception guides food selection, predator avoidance, social communication, reproduction, and homeostatic regulation. Some definitions expand the term to include internal kemoreception, the sensing of chemical states such as pH, carbon dioxide, and osmolarity that inform physiological responses.

Mechanisms rely on specialized chemoreceptor cells. In vertebrates, olfactory receptor neurons express diverse G protein-coupled receptors that bind volatile odorants, triggering second-messenger cascades and opening ion channels to produce electrical signals. Taste receptor cells use distinct receptor families: sweet, umami, and bitter tastes are detected by GPCRs of the T1R and T2R families, while sour and salt involve ion channels. Signals are relayed to the brain via cranial nerves (olfactory nerve I for smell; facial VII, glossopharyngeal IX, and vagus X for taste) and processed in brain regions such as the olfactory bulb and gustatory cortex, respectively. Some species also rely on chemesthesis, the detection of chemical irritants via somatosensory pathways (for example via TRP channels) that contribute to sensations of heat, cold, or burning.

Chemoreception is studied across diverse organisms. In insects, odorant receptors function with a co-receptor and distinct signaling mechanisms. In vertebrates, kemoreception integrates with behavior and physiology, influencing feeding, mating, circadian rhythms, and hormonal regulation. Understanding kemoreception has applications in flavor and fragrance industries, pest management, and medical diagnostics through olfactory testing and chemosensory disorders.