Even with their well-developed senses of sight and hearing, it’s smells that make a dog’s world.
Of all the canine super-senses, the dog’s ability to detect scent is the most extraordinary and furthest removed from humans. The dog’s scent-described world is so different to a human’s that it’s almost impossible for most people to imagine.
It all comes down to the number of scent-receptor cells nature has given each species. A human has 5 million specialized scent-receptor cells in its nose whereas a dog has almost 200 million. Certain breeds have even more. A tracking dog such as a Bloodhound can have up to 300 million scent receptors.
But what does that mean? A dog can recognize over a million scent patterns. Humans can manage about a thousand. It also means that dogs can smell scents even at very low concentrations.
Survival tools from distant relations
This extraordinary power of smell evolved in the dog’s earliest wolf-like ancestors. Along with well-developed hearing and sight, powerful scent-receptors help dogs to hunt, avoid predators, and recognize territories. To hunt and scavenge year-round, even in the winter when snow covers the ground, a heightened sense of smell helped dogs find food they couldn’t see.
Dogs can breathe in and out at the same time. Lifting the head and flaring the nostrils to breathe in maximizes the amount of air passing over the receptor cells. A dog can continue to breathe out through its mouth while breathing in through its nose, keeping up a constant airflow and allowing the animal to amass more olfactory information.
Have you ever tested the wind direction by licking a finger and holding it up in the air? The moisture makes your finger more sensitive to temperature changes caused by the wind, helping you to judge its direction. Dogs have extended tear ducts that run into the nose, keeping it moist. A dog’s wet nose helps it to tell from where a particular scent is coming. The water in its nasal cavity also dissolves scent molecules, helping the dog to distinguish more subtle odors.
More smell per sniff
But picking up a scent is only part of a dog’s remarkable ability with smells. Once the dog’s nose detects scent molecules, they travel to a complex, super-sensitive membrane folded over a lattice of thin bones. This membrane and lattice acts like a net, capturing all the molecules. A mass of sensory cells in the membrane convert the molecules into electrochemical impulses and transmits them to the brain.
Humans who rely on sight have a large visual cortex to process information from the eyes. In dogs, the olfactory cortex is more developed. The olfactory cortex decodes the electro-chemical messages from the nose and triggers the animal’s responses.
Dogs’ whiskers also link to the olfactory cortex. Dogs can smell with their whiskers, too! A dog’s mouth also harbors an additional organ not present in humans, which captures and transmits scent molecules in a similar way to the nose.
Of the dog’s astonishing super-senses, its sense of smell is the most remarkable. It’s also the one which sets dogs apart from humans. The scent-receptors and the olfactory cortex contribute the largest amount of information which a dog uses to build its perceptions of the environment. When it comes to smells, dogs and humans live in two different worlds.
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