Snuffle. Sniff. Snort. Repeat.
So goes man’s best friend as he ambles odiferously through his daily routine. Everyone knows that canines have epic olfactory capabilities, but just how great is the doggie sense of smell and how is it accomplished?*
To start with, the anatomy of a dog’s nose is magnificently designed to maximize odor detection. The number of scent receptors for humans is about 5 million, for a dog it ranges from 125 to 300 million, depending on the breed (with Blood hounds being the heavyweight champion of odor detection). This means that dogs can smell somewhere between 10,000 to 100,000 times better than humans. To give you an idea of the difference several million receptors make, imagine if this were vision instead of smell and a dog could see only 10,000 times better than you can. In this case, if you stood at the Farmer’s market in Granville and looked up Broadway to Whit’s ice cream, a total of 338 feet, then your dog could see clearly, all the way to Hilton Head Island, South Carolina, 647 miles away. If, dogs smell 100,000 times better and taste were the analogy, then where we can detect a teaspoon of sugar in our coffee, a dog could detect 1 teaspoon in a million gallons of water.*
The anatomical structure of a dog’s nose also aides super powers of an olfactory nature. Humans breathe in and out and we have no dedicated pathway for odor detection. Our “sense of smell is relegated to a small region on the roof of our nasal cavity, along the main airflow path.”* When a dog breathes in, the air is divided in two. 88% is devoted to respiration and 12% heads directly to the dog’s olfactory center. (See Figure A). Imagine for a moment how wonderful it would be to wake up to the smell of cinnamon rolls on a Sunday morning if the smell wasn’t filtered but instead channeled directly into our brains!
Dogs inhale throughout he central part of the nostril and the aerodynamic design of the central nostrils aids them in determining which nostril the odor entered. They exhale through the slits in the sides of their noses which “actually helps usher new odors into the dog’s nose. More importantly, it allows dogs to sniff more or less continuously.”* Thus, dogs can quickly pick up more scents as well as determine from whence they came.
Now, if all of this weren’t cool enough, they also have a second scent detection system called the vomeronasal organ (VNO) or Jacobson’s organ.** Also found in a variety of animals, including snakes, tigers, tapirs, and horses (See figure to the the left), the VNO is generally assumed to be important in detecting pheromones “that advertise mating readiness and other sex-related details.”* It may also cause physiological or behavioral changes in animals. For example, “[i]nduction of uterine growth and estrus in female prairie voles normally resulting from exposure to males is also dependent on an intact VNO.”** Who knew? Vole secrets revealed!
A dog’s vomeronasal organ is located in the bottom of the dog’s nasal passage. “The pheromone molecules that the organ detects—and their analysis by the brain—do not get mixed up with odor molecules or their analysis, because the organ has its own nerves leading to a part of the brain devoted entirely to interpreting its signals. It’s as if Jacobson’s organ had its own dedicated computer server.”* While it is generally accepted that the VNO detects pheromones, the full function of the VNO is not entirely understood. This may explain, in part, why your dog likes to carry around your smelly sock, underwear, or t-shirt: it has your distinctive smell on it and carrying it around puts your scent close to him, literally!***
We are often told that we ought to stop and “smell the roses.” So, even though a well trained dog should walk along with you when you want him to do so, think about how he perceives the world and allow him the occasional luxury of leisurely smelling the smorgasbord of smells that await him on every block.
* This is a great synopsis of our dog’s phenomenal olfactory abilities: http://www.pbs.org/wgbh/nova/nature/dogs-sense-of-smell.html
**Whether or not adult humans have a VNO and what function(s) it might perform has been a long-standing debate. “Recent endoscopic and microscopic observations suggest that here is an organ on at least one side in most adults. This review enquires into its function.” Human Vomeronasal Organ Function: A Critical Review of Best and Worst Cases (http://chemse.oxfordjournals.org/content/26/4/433.full)
*** In humans, apocrine glands are located in specific areas such as the armpits and groin area. These glands secrete information about our age, sex, health, emotional state, etc. This information is specific to each person, thereby giving your dog something highly personal to hang on to. The Canine Senses (http://www.responsibledog.net/canine_senses.html)
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