chemoreception

Chemoception is the sensory process by which organisms detect chemical stimuli in the external environment or within their bodies. It includes olfaction (smell) and gustation (taste) in many animals, as well as specialized chemical sensing such as pheromone detection and chemesthesis (chemical irritation). Chemoception guides critical behaviors, including food choice, avoidance of toxins, mating, navigation, and social communication, shaping ecological interactions and survival.

In olfaction, odorant molecules bind to receptors on olfactory sensory neurons in the nasal epithelium. Most vertebrate odorant receptors are G protein-coupled receptors that initiate intracellular signaling cascades leading to neuron depolarization and transmission to the olfactory bulb. The olfactory system encodes patterns of activity across receptor types, enabling discrimination of thousands of odorants. In gustation, taste receptor cells within taste buds transduce chemical stimuli into neural signals. Sweet, umami, and bitter tastes involve GPCRs, while salty and sour involve ion channels. Signals travel via cranial nerves to the brainstem and gustatory cortex, where they contribute to flavor perception and nutrient assessment.

Chemoreception is not limited to vertebrates. Insects rely on a family of odorant and gustatory receptors, often expressed in antennae and mouthparts, to detect food sources, mates, and predators. Some organisms rely on pheromones for social communication. The neural coding of chemical information can be combinatorial, with many receptors broadly tuned and each chemical activating a subset of receptors, enabling rich odor landscapes from comparatively few receptor types.

Disruptions to chemoreception can affect nutrition, safety, and quality of life, as in anosmia (loss of smell) or ageusia (loss of taste). Research explores receptor biology, signal transduction, neural representation, and applications in flavors, fragrance, pest control, and medical diagnostics.