Orthonasal

Orthonasal olfaction refers to the sense of smell as odorants are detected through the nostrils during inhalation. Volatile molecules enter the nasal cavity via the external nares and travel to the olfactory epithelium in the upper part of the nasal cavity, where they bind to olfactory receptors on sensory neurons. These signals are transmitted to the olfactory bulb and then to higher brain regions, where odor identity and qualities are processed.

This pathway is distinct from retronasal olfaction, in which odorants originate in the mouth and move from the oral cavity to the nasal cavity during chewing and swallowing, contributing to flavor perception. While the same receptor families can be activated by orthonasal and retronasal stimuli, the route, context, and resulting perceptual experience differ; orthonasal and retronasal inputs combine to form the overall aroma and flavor experience.

In clinical and research settings, orthonasal olfaction is commonly assessed with sniff tests or olfactometry to evaluate detection thresholds, discrimination, and identification of odors, isolating nasal odor perception from gustatory input. Impairments of orthonasal smell occur in olfactory disorders such as hyposmia or anosmia and can affect everyday detection of environmental odors, warnings, and fragrances.

Etymology and usage: The term orthonasal combines ortho- meaning straight or normal and nasal, contrasting with retronasal, which describes odorant passage from the mouth through the pharynx to the nasal cavity. The concept is widely used in olfactory science, sensory psychology, fragrance research, and food science to distinguish routes of odor perception.