Olfactory receptors (synonym olfactory receptors) are responsive to chemical stimuli receptors ( chemoreceptors ), in particular in the perception of smell ( olfaction ) are involved. In addition, olfactory receptors also occur in organs that are not involved in the perception of smell (eg, in the liver and testes ). Olfactory receptors are G- protein -coupled receptors. The number of different olfactory receptors of humans is about 350, while the dog has about 1200 different olfactory receptors.
Synonymous with the term olfactory receptor in physiology also used for nerve cells that are responsible for the olfactory perception ( see olfactory receptor ( cell) ).
Olfactory receptors are target molecules for odor, which can bind to it and activate the olfactory receptor. This olfactory receptors show selectivity for different odorants. At the extracellular end of the olfactory receptor, the seven spans the cell membrane, the receptor protein forms a pocket. This bag is a docking site for the fragrance molecule with which it can connect according to the key - lock principle. Due to their molecular structure, only certain molecules with the bag can connect. Therefore, the odorant receptor for that particular molecule or group of structurally-related molecules is specific. However, minor changes in the protein structure lead to changes in the overall conformation of the docking site and the specificity of the olfactory receptor.
After binding of the odorant to the receptor protein results in a conformational change that results in activation of the protein and the appended G- protein (Golf). This complex of receptor and G protein is responsible for the forwarding of the olfactory stimulus in the cell interior ( signal transduction). Activating the enzyme adenylyl cyclase, which catalyzes the conversion of ATP to cAMP and thus the concentration of this second messenger in the increased cilia. This second messenger in turn activates protein kinases that ion channels can open at the cell membrane, thereby affecting the membrane potential. For these channels, there are two different ion channels. The first is a non-specific channel can flow into the interior of the cell by the positive sodium and calcium ions. The influx of calcium ions activates the second channel, which is specific for the negative chlorine ions, which now flow out of the cell. The result is a depolarization that can generate an action potential in the axon hillock of odorant receptor. This signal is transmitted via the olfactory bulb and the olfactory tract later for evaluation of olfactory perception in the central nervous system.
The biggest recent success in the study of olfaction achieved by the two American researchers Linda Buck and Richard Axel, who could identify with their genetic research about 1000 responsible for the olfactory receptors genes and for 2004 received the Nobel Prize in Medicine. These are about 3% of the human genome. These genes determine the protein structure of the receptor protein and thus its specificity. Currently, only 6 of the 350 olfactory receptors of the body are explored in more detail.