Luktesansen

Luktesansen is the sense by which organisms detect airborne chemical compounds, enabling the perception of odors. In humans, it contributes to flavor perception, food preferences, hazard detection, and social communication, and it interacts with memory and emotion through connections to brain regions such as the olfactory cortex and limbic system.

Anatomy and physiology

Olfactory function begins in the olfactory epithelium, a specialized tissue in the roof of the nasal cavity. The epithelium contains olfactory receptor neurons, supporting cells, and basal stem cells. Each olfactory neuron expresses one type of G protein–coupled odorant receptor from a large gene family. Odorant molecules bind to these receptors, triggering a signal transduction cascade that starts at the receptor and leads to electrical activity in the neuron. Axons of these neurons pass through the cribriform plate to the olfactory bulb, where signals converge in structures called glomeruli. From there, mitral and tufted cells relay information to higher brain regions, including the piriform and entorhinal cortices, amygdala, and orbitofrontal cortex, allowing odor identification and conscious perception as well as emotional associations.

Receptors, regeneration, and perception

Humans have hundreds of olfactory receptor genes, with thousands of receptor proteins contributing to a broad range of detectable smells. Olfactory receptor neurons continually regenerate from basal stem cells, maintaining sensory function over a lifetime. Smell perception involves not only detection but discrimination and identification, which are influenced by experience, context, and integration with gustation and memory.

Clinical and diagnostic aspects

Loss or distortion of smell is known as anosmia, hyposmia, or dysosmia, and can result from infections, head trauma, allergic conditions, or neurodegenerative diseases. Diagnostic approaches include standardized smell tests such as the Sniffin’ Sticks and the University of Pennsylvania Smell Identification Test (UPSIT). Olfactory training or rehabilitation is sometimes recommended for certain forms of olfactory impairment.

Evolution and variation

Olfaction is highly important for survival in many species, aiding foraging and predator avoidance. In humans, sensitivity varies and is generally less acute than in many animals, but the sense remains integral to flavor, safety, and social signaling.