hajuaistissa

Hajuaisti, or the olfactory sense, is the sensory system by which mammals and other organisms detect volatile chemical compounds in the air. The phrase hajuaistissa can be used in Finnish to refer to perception or processing "in the olfactory sense." The olfactory system detects odorants through receptors in the olfactory epithelium of the nasal cavity. Humans have a large family of olfactory receptor genes, allowing detection of thousands of odorants, though sensitivity varies among individuals.

Olfactory receptor neurons extend from the epithelium and send signals via the olfactory nerve to the olfactory bulb, which contains glomeruli where signals from receptor types converge. From the bulb, information is relayed to higher brain regions such as the piriform cortex, entorhinal cortex, amygdala, and orbitofrontal cortex, where odor quality, intensity, and hedonic value are integrated with memory and emotion.

The sense contributes to flavor perception, hazard detection (for example, smoke or spoiled food), and social communication. It operates alongside the trigeminal system, which mediates chemesthetic sensations such as irritation or cooling.

Olfactory function can be affected by aging, infections, trauma, or disease. Conditions include anosmia (loss of smell), hyposmia (reduced smell), parosmia (distorted smell), and phantosmia (olfactory hallucinations). Assessment is done with olfactometry tests such as Sniffin’ Sticks or the University of Pennsylvania Smell Identification Test.

Evolutionarily, the olfactory system is ancient and varies across species in sensitivity and receptor repertoires, reflecting ecological needs. In humans, the sense contributes to food choice, mate selection, and environmental awareness, although it is often integrated with other senses in the perception of the external world.