What we do not know about olfaction. Part 1: from nostril to receptor.

The sense of smell is still mysterious in many ways, despite the advances of the past few years. This review gives a broad overview of the state of the field by examining each step of the process of signal transduction from odorant to brain. Each subject section was searched individually in Pubmed, ISI Web of Science and Google Scholar as well as materials known to the author. The results are sequentially presented in order of anatomical progression of the signal. The review finds many surprising and interesting theories, facts and methods worthy of further research.