[Olfaction: from nose to cortex].

Olfactory physiology involves four main steps: nasal airflow perireceptor events, transduction, and central olfaction. Complex and diverse physiological processes are involved at each step and may be undermined by numerous pathological processes. Nasal airflow physiology involves fluid mechanics and specifc physicochemical properties of odorants; its main pathology is nasal polyposis. Perireceptor events involve transport molecules and enzymes which eliminate xenobiotics; its main pathology is chronic rhinitis. Transduction is the role of primary olfactory neurons, which detect and discriminate various chemical molecules across a wide range of concentrations. To fulfill this task, these cells use a large family of G protein-coupled receptors (odorant receptors). The main pathology is acute viral rhinitis affecting the olfactory organ. Finally, after olfactory signals are generated, the information is processed and coded in the olfactory bulb before being disseminated to several areas of the brain; its pathology is dominated by neurodegenerative disorders.