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Olfaction Olfaction, the act or process of smelling, is a dog's primary special sense. A dog's sense of smell is said to be a thousand times more sensitive than that of humans. In fact, a dog has more than 220 million olfactory receptors in its nose, while humans have only 5 million. Because of this keen sense of smell, dogs are able to locate everything from forensic cadaver material to disaster survivors as demonstrated during the terrorist attack on the World Trade Center on September 11, 2001.

Anatomy

A dog's nose consists of a nasal cavity and a pair of nostrils (nares) for inhaling air and odors. The olfactory receptor cells in a dog's nose extend throughout the entire layer of specialized olfactory epithelium found on the ethmo-turbinate bones of the nasal cavity. The olfactory portion of the nasal mucous membrane contains a rich supply of olfactory nerves that ultimately connect with the highly developed olfactory lobe in the dog's brain.

Dogs possess an additional olfactory chamber called the vomeronasal organ that also contains olfactory epithelium. The vomeronasal organ, known as Jacobson's organ, consists of a pair of elongated, fluid-filled sacs that open into either the mouth or the nose. It is located above the roof of the mouth and behind the upper incisors. Interestingly, the olfactory receptors in the nasal cavity are anatomically distinct from those in the vomeronasal organ. Each receptor neuron (nerve cell) in the olfactory epithelium of the nasal cavity has a dendrite that ends in a knob with several thin cilia covered by mucus. Receptor neurons in the vomeronasal organ typically lack cilia but have microvilli on the cell surface.
 

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