18 different members of a multigene family encoding seven transmembrane domain proteins have been identified to be involved in olfactory expression. Studies suggest detection of chemically distinct odorant result from the association of odorous ligands with specific receptors on olfactory neurons. However, the receptors themselves have yet to be identified. Olfactory sensory neurons are bipolar. Its Dendritic processes extend to the mucosal surface and give rise to a number of specialized cilia. Its axons project to the olfactory bulb of the brain towards subcortical and cortical regions for discrimination of odors. Recent experiments have yielded results and data that indicate a family of genes transducing signald via GTP-binding proteins encoding thousands of different receptors likely to only recognize a small number of odorants.