Smell receptors. Coloured transmission electron micrograph (TEM) of an olfactory neurone (blue). This nerve cell is found in the nasal epithelium. The swollen part of the cell is the olfactory vesicle. Protruding from it are small hairs (cilia). These are the smell receptors. The information from these receptors is passed to the olfactory bulb in the brain where it is processed. In order for a substance to be smelled it must be a gas, and water and lipid soluble. There are over a million olfactory receptor cells in a human nose, all located in a small area at the back of the nasal cavity. Magnification: x 10,000 when printed 10 centimetres wide.