In case you
have not noticed, your dog's world revolves around his nose. Dog's
noses are not like our noses. They are so much more! In fact, a dog uses its nose much
like humans use their hands. Dog’s noses are highly sensitive
and when those tissues are dry and chapped, it can be very painful to your pup.
Olfaction, the act or process of smelling, is a dog's primary special sense. A dog's sense of smell
is said to be a thousand times more sensitive than that of humans. In fact, a dog has more than
220 million olfactory receptors in its nose, while humans have only 5 million. Because of this
keen sense of smell, dogs are able to locate everything from forensic cadaver material to disaster
survivors as demonstrated during the terrorist attack on the World Trade Center on September 11,
2001.
A dog's nose consists of a nasal cavity and a pair of nostrils (nares) for inhaling air and odors.
The olfactory receptor cells in a dog's nose extend throughout the entire layer of specialized
olfactory epithelium found on the ethmo-turbinate bones of the nasal cavity. The olfactory portion
of the nasal mucous membrane contains a rich supply of olfactory nerves that ultimately connect
with the highly developed olfactory lobe in the dog's brain.
Dogs possess
an additional olfactory chamber called the vomeronasal organ that also contains olfactory epithelium.
The vomeronasal organ, known as Jacobson's organ, consists of a pair of elongated, fluid-filled
sacs that open into either the mouth or the nose. It is located above the roof of the mouth and
behind the upper incisors. Interestingly, the olfactory receptors in the nasal cavity are anatomically
distinct from those in the vomeronasal organ. Each receptor neuron (nerve cell) in the olfactory
epithelium of the nasal cavity has a dendrite that ends in a knob with several thin cilia covered
by mucus. Receptor neurons in the vomeronasal organ typically lack cilia but have microvilli
on the cell surface.
A dog's nose should be cool and moist. A dry and or warm nose indicates an unhealthy and uncomfortable
nose. The moisture secreted by mucous glands in the nasal cavity captures and dissolves molecules
in the air and brings them into contact with the specialized olfactory epithelium inside the nose.
Dogs use sniffing
to maximize detection of odors. The sniff is actually a disruption of the normal breathing pattern.
Sniffing is accomplished through a series of rapid, short inhalations and exhalations. A bony
subethmoidal shelf, which is found below the ethmo-turbinate bones of the nasal cavity, forces
inhaled air into the olfactory epithelium. Washing out of the region upon exhalation does not
occur due to the nasal pocket created by the bony subethmoidal shelf. The nasal pocket permits
the odor molecules that are unrecognizable in a single sniff to accumulate and interact with
olfactory receptors. Odor molecules in the olfactory epithelium of the nasal cavity are absorbed
into the mucous layer and diffuse to the cilia of receptor neurons. This interaction generates
nerve impulses that are transmitted by the olfactory nerves to the dog's brain, which has a well-developed
olfactory lobe. This allows the dog to recognize a scent and follow a trail.
Olfactory
receptor cells in the vomeronasal organ also send impulses to the region of the hypothalamus
associated with sexual and social behaviors. This organ is believed to be important in the detection
of pheromones (body scents). This theory could account for the dog's ability to identify and
recognize other animals and people.
