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 concentration.
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
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 which 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.
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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