information:extraction
Mechanism

Odorants are small molecules present in the environment that bind receptors on the surface of cells called olfactory receptor neurons (ORNs). ORNs are present in the olfactory epithelium which lines the nasal cavity and are able to signal due to an internal balance of signal molecules which vary in concentration depending on the presence or absence an odorant. When odorants bind receptors on ORNs, Ca 2+ ions flood into the cell causing depolarization and signaling to the brain. Increased Ca 2+ also activates a negative, stabilizing feedback loop which lowers the olfactory neuron's sensitivity the longer it is stimulated by an odorant to prevent overstimulation. This happens by limiting the amount of cyclic AMP (cAMP) in the cell and by making the Ca 2+ -importing channels which cAMP binds to less responsive to cAMP, both effects reducing further intake of Ca 2+ and thus limiting depolarization and signaling to the brain. It is important to note that the same mechanism which allows for signaling also limits signaling for prolonged periods of time, the first cannot occur without the second.