September 05, 2019
K9 Super power
Dogs are famous for their sense of smell, but do you know just how much of a super power it really is?
Often damp, sometimes wriggling but always cute as a button, your dog’s nose helps them interpret their world. A dog’s ability to smell is nothing short of incredible!
Superior sniffer design
When we try to smell something, we breathe air in through the nose. When we need to exhale, the air goes back out the nose, taking the smell with it. Dogs have thought this through a little better! They can separate out their inhaled breath into two components – one for breathing and one for smelling. The portion of air that’s used for sensing smell goes to a specialised lining in the back of the nasal cavity, just in front of the brain, called the olfactory epithelium. Some idea of the importance of their sense of smell can be gained from the surface area of this epithelium, which is 18-150 cm2 in dogs (depending on breed), 21 cm2 in cats, but only 3-4 cm2 in humans. So dogs have an ability to store smell in their nose, while continuing to breathe in and out.
The olfactory epithelium is covered by a layer of mucus, into which airborne molecules which cause sensation of odour must dissolve before they can be detected by special chemical receptors. Each receptor is a nerve cell, which transmits information to other nerve cells in the olfactory part of the brain.
Dogs have up to 300 million olfactory receptors in their noses, compared to only around 6 million for us. Plus the region of their brain dedicated to interpreting these is about 40 times larger than ours. This means that your dog’s sense of smell is up to 100,000 times better than yours! To put that into perspective, a dog can detect a teaspoon of sugar in two Olympic-sized swimming pools!
Dogs also have the ability to smell separately with each nostril, which helps them locate the source of a smell. When dogs deliberately sniff objects, the duration of the sniffs is adjusted to allow optimum exposure of the olfactory epithelium to the stimulus. If a stimulus is weak, dogs tend to increase the rate of sniffing, rather than the duration of each sniff.
Dogs also possess something called the vomeronasal organ, which we humans don’t have. This organ detects special chemicals called pheromones and comes with its own nerves and specialised part of the brain.
Dogs not only have a well-developed olfactory sense, but are also readily trained and this combination of skills has been utilised for thousands of years for the hunting, tracking and retrieving of game.
The tracking skills of dogs depend on their ability to detect the volatile fatty acids found in human sweat, in concentrations which are hundreds or thousands of times lower than our own threshold for smell. Dogs can also detect whole human odours, even those derived from fingerprints, both when fresh and following a week or more of weathering. Perhaps most impressive is a dog's ability to detect features specific to the individual in all the body odours (palm, armpit, sole) from a single person, even though these regional odours smell quite different to us.
The ability of trained dogs to distinguish between different people has been investigated using pairs of identical twins. In tracking experiments, when direct comparisons could be made, the twins could be reliably discriminated, but in successive choices the same dogs indicated that the twins were much more similar to each other than to other humans. In other words, tracking dogs can tell people apart by their smell, about as well as we can by sight.
So next time you notice your dog wriggling their nose, you'll appreciate just how much is going on under the surface!