 | 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. |
http://www.aces.edu/pubs/docs/U/UNP-0066/UNP-0066.pdf
Anatomy
A dog's nose consists of a pair
of nostrils (nares) for inhaling
air and odors and a nasal cavity.
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
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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.
highly developed olfactory lobe
in the dog's brain.
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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.
| 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.
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Physiology A dog's nose is normally cool
and moist. 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 ethmoturbinate
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. |
Utility
Today, people use a dog's keen
sense of smell in many ways.
Federal, state, and local government
agencies employ specially
trained dogs in search and rescue
missions and in the detection of
narcotics and contraband agriculture
products. The Federal
Emergency Management
Agency has national dog-handler
teams that respond to disasters
worldwide. State and local law
enforcement agencies in the
United States (U.S.) have canine
units trained to detect drugs and
search for lost individuals,
homicide victims, and forensic
cadaver materials. | U.S. Customs and Border
Protection has more than 800
canine teams that work with the
U.S. Department of Homeland
Security to combat terrorist
threats, stop the flow of illegal
narcotics, and detect unreported
currency, concealed humans, or
smuggled agriculture products.
Its Canine Enforcement Program
(CEP) uses a variety of dogs
including Labrador retrievers,
golden retrievers, German shepherds, Belgian Malinois, and
many mixed breeds. | The CEP uses beagles to detect
agriculture contraband. The
passively trained Beagle Brigade
dogs detect prohibited fruits,
plants, and meats in baggage and
vehicles of international travelers
as they go through Federal
Inspection Service areas. Beagle
Brigade teams work at several
major border-crossing stations in
the United States as well as many
international airports that are
ports of entry into this country.
Medical tests have recently
shown that specially trained dogs
are capable of detecting certain
types of tumors in humans. |
References:
American Rescue Dog Association. (2nd ed.) (2002). Search and rescue dogs: Training the k-9 hero. New York, NY: Howell Book House, Wiley Publishing, Incorporated. Campbell, K. L., Corbin, J. E., & Campbell, J. R. (2005). Companion animals: Their biology, care, health, and management. Upper Saddle River, NJ: Pearson Education, Incorporated. Case, L. P. (1999). The dog: Its behavior, nutrition, and health. Ames, IA: Iowa State University Press. Gerstenfeld, S. L., & Schultz, J. L. (1999). ASPCA complete guide to dogs. San Francisco, CA: Chronicle Books LLC. Giffin, J. M., & Carlson, L. (3rd ed.) (2000). Dog owner's home veterinary handbook. New York, NY: Howell Book House, Hungry Minds, Incorporated. Guthrie, S., Lane, D., & Sumner-Smith, G. (2001). Ultimate dog care. Lydney, Gloucestershire, UK: Ringpress Books. Randall, D., Burggren, W., & French, K. (5th ed.) (2002). Eckert animal physiology: Mechanisms and adaptations. New York, NY: W.H. Freeman and Company. Reece, W. O. (12th ed.) (2004). Dukes' physiology of domestic animals. Ithaca, NY: Cornell University Press. Whitehead, S., Viner, B., Cuddy, B., & Sullivan, K. (1999). Dog: The complete guide. London, UK: Team Media
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