Luktsensen

Luktsensen, or the sense of smell, is the chemosensory system that detects volatile odorant molecules in the environment. It contributes to flavor perception, detects hazards such as smoke or spoiled food, and influences memory and emotion through connections with the limbic system.

Anatomy: The primary sensory apparatus is the olfactory epithelium, a specialized tissue lining the roof of the nasal cavity that contains olfactory receptor neurons. Each neuron expresses one odorant receptor gene from a large receptor family. Their axons converge to the olfactory bulb, where signals are organized into glomeruli and transmitted by mitral and tufted cells to higher brain regions.

Physiology: Odorant molecules bind to receptors, triggering G-protein–coupled signaling, increasing cyclic AMP, and opening ion channels to generate action potentials. This information travels from the olfactory bulb to the piriform cortex and other areas, including the amygdala and entorhinal cortex, linking odor identity to affect and memory. Humans detect many odorants using hundreds of receptor types.

Development and variation: Sensitivity develops in early life and changes with age, genetics, and exposure. Conditions such as anosmia (loss of smell), hyposmia (reduced smell), parosmia (distorted smell), and phantosmia (olfactory hallucinations) are recognized clinical phenomena with various causes, including infections, head injury, sinus disease, and neurodegenerative disorders.

Testing and evolution: Smell is assessed with standardized tests such as UPSIT and Sniffin’ Sticks. The sense has evolved differently across species, with numerous odorant receptors in many mammals. The discovery of odorant receptors and the organization of the olfactory system by researchers such as Richard Axel and Linda Buck underpins current understanding.