orthonasalis

Orthonasal, also spelled orthonasalis, is a term used in anatomy and sensory science to describe olfactory perception that occurs when odorants enter the nasal cavity through the external nares (the nostrils). It contrasts with retronasal olfaction, in which volatile compounds reach the olfactory receptors from the oropharynx during eating or drinking. The orthonasalis route is the primary pathway for most environmental odors, while retronasal input is closely linked to flavor perception.

Anatomy and physiology follow a common olfactory pathway. Odorants inhaled through the nostrils dissolve in mucus and bind to receptors on olfactory receptor neurons in the olfactory epithelium located in the superior nasal cavity. Signals are transmitted via the olfactory nerve to the olfactory bulb and then to higher brain regions, including the piriform cortex, amygdala, and orbitofrontal cortex, where odor identity and emotional associations are processed.

In research and clinical practice, orthonasalis olfaction is often assessed separately from retronasal olfaction. Olfactometry and nasal sniff tests deliver odors nasally to measure thresholds, discrimination, and detection accuracy for the orthonasalis route. Differences between orthonasalis and retronasal perception can influence fragrance evaluation, environmental odor reporting, and the diagnosis of olfactory disorders.

Clinically, conditions such as nasal obstruction, chronic rhinosinusitis, or head trauma can impair orthonasalis olfaction. Understanding orthonasalis function is important for diagnosing anosmia and guiding treatments, as well as for interpreting the sensory contributions of ambient odors versus flavors during eating.