Useful Information

What is odour and how do we smell it?

Odour is the property of certain substances, in very small concentrations, to stimulate chemical sense receptors that sample the air surrounding a person.

Smell, also called olfaction, is the detection and identification by sensory organs of airborne chemicals. Olfaction depends primarily on chemically sensitive nerves with endings in the lining (epithelium) of the nasal cavity.

Olfactory receptor cells are present in very large numbers, forming an olfactory epithelium within the nasal cavity. The human olfactory epithelium covers about 5–10 sqcm and has about 10–40 million olfactory receptor cells. Each receptor cell has a single external process that extends to the surface of the epithelium and gives rise to a number of long, slender extensions called cilia. The cilia are covered by the mucus of the nasal cavity. The olfactory receptor cells have axons that connect directly to the brain, allowing substances to be sensed. Olfactory receptor cells are continually replaced, with new cells developing from basal cells in the olfactory epithelium. In humans the receptor cells are replaced about every 60 days.