 Dear students, in this topic we shall discuss the mechanism of olfactory reception. The olfactory receptors are neurons with long dendrites and axons. They are located inside the nasal cavity and they send impulses directly to the olfactory bulb of the brain. Dear students, the olfactory receptor neuron has a long thin dendrite that terminates in a small knob-like structure at its surface. The knob has about 4 to 25 olfactory cilia at its tip. These cilia are about 200 micrometer long. These cilia are covered by a proteinaceous mucus. Now we shall discuss the mechanism of olfactory transduction. Dear students, these adduent molecules are absorbed into the mucus layer and then they are delivered to the cilia. In the cilia, they bind to a receptor protein. The receptor protein is coupled to a G protein. This G protein activates the enzyme adenyl cyclase that converts an ATP into cyclic AMP. The cyclic AMP opens ion channels that are permeable to both sodium and calcium. As a result of calcium inflow, colorite channels also open. Both these factors that is the opening of and inflow of calcium ions and outflow of colorite ions results in the depolarization of membrane of olfactory receptor cell. As a result, the action potentials are generated and these action potentials are transmitted to the central nervous system by the olfactory nerve. This mechanism of transduction through a G protein linked receptor ensures that the stimulus received by certain adduent molecules is amplified multiple times. This increases the sensitivity of olfactory receptors. The students now we shall discuss the basis of differentiating different types of smells. The receptor proteins that are involved in the olfactory transduction and are present in the olfactory cilia of receptor cells, these proteins belong to a very large family of proteins. These proteins are expressed only in the olfactory cells. These proteins have very small variations in their structures. So all these proteins can perform the same function of olfaction but with small variations. As a result of these variations, these proteins have many subtypes and each subtype is specialized to receive a particular type of chemical substance that is an odorant. This forms the basis of differentiation, the ability to differentiate a large number of chemical compounds that have different smells.