Explain signal transduction (changing from a chemical signal to a nerve impulse) for the sense of smell.

The odorant molecules arrive either directly by diffusion into the mucus, or are supported by transport proteins (odor binding protein or OBP) that allow the hydrophobic molecules - majority - to penetrate the mucus covering the epithelium, and thus to reach the membrane receptors present on the eyelashes of the olfactory neurons. These transport proteins are thought to concentrate odorant molecules on membrane receptors. As ligands, the odorant molecules bind to membrane receptors on the eyelashes, triggering a transduction pathway for a stimulus involving G.olf protein (first messenger), adenylate cyclase, and cAMP ( second messenger). The second messenger causes the opening of ion channels Ca2 + / Na + present on the plasma membrane of the olfactory receptor, these two ions then enter the cell. Ca2 + causes the opening of a Cl- channel, the output of this ion causes depolarization of the membrane so that the olfactory receptor produces action potentials. These impulses will go directly to the olfactory bulb, in the prefrontal region of the brain, where this information (and that of taste) is processed by the body.