Canines can have as many as 230 million olfactory receptors, and if unfolded would cover an area as large as a handkerchief. To give some perspective, a human has around 5 million olfactory receptors, and if unfolded would only cover the area of a postage stamp. Dogs also possess a special olfactory receptor organ called Jacobson’s organ. Due to their extraordinary sense of smell, canines are often used in work that involves tracking scents.
Working from the outside in, the canine nose has a pair of nostrils for inhaling air and odors, which then flow through the nasal cavity. The nasal cavity is separated into two chambers by a septum, which is made of cartilage and bone. In the chambers are a maze of spongy spiraled bones, or turbinate bones, that direct air flow. The olfactory receptors and nerves are found throughout this maze of bones, and eventually connect with a specially developed olfactory lobe in the canine brain.
Canines detect scents either by sniffing the air or the ground in a series of rapid and short inhalations and exhalations, which maximizes the intake of an odor to the olfactory receptors. Odors that are not recognized in the first sniff accumulate and interact with the olfactory receptors and get absorbed into a mucous layer covering the turbinate bones. The odor molecules are then dispersed by the olfactory receptors to the nerves, creating nerve impulses that get transmitted to the olfactory lobe in the brain. This is how canines are able to recognize scents and follow them.
Canines possess an organ in the upper part of the mouth called Jacobson’s Organ. Unlike the regular olfactory receptors that transmit to the olfactory lobe, this organ contains unique nerve cells that communicate with the part of the brain that relates to mating and emotion. Canines utilize it simply by opening their mouth while sniffing, allowing the hormones to flow through the organ to the brain to be processed. The main function of Jacobson’s Organ is the detection of pheromones and other hormones, so it is more of a hormone receptor than a scent receptor. Pheromones provide canines with information regarding breeding availability. Jacobson’s Organ allows canines to differentiate between people and other animals through their hormone scent.
Due to their superior sense of smell, canines are utilized for many tasks. Scent dogs are used for search and rescue, finding cadavers, detecting explosives, firearms, and drugs, and even cancer in human patients. Canines have long been used for hunting because they can track the scent of an animal for a long way.