Canine Anatomy

While a wet nose can help to determine good health, it shouldn’t be relied upon. A dogs nose may be dry for reasons other than poor health, and other factors such as lethargy, poor appetite, behavior change etc. should be relied upon more to determine good health, rather than a wet nose.

So why is a dogs nose wet?
Scientists have speculated for years that the reason behind the wet nose was to help with scenting (as scent molecules tend to hold better in wet rather than dry). In 2008 a study was done on 54 dogs that determined the wet nose is, in fact, there to help with scenting. However, rather than to simply trap molecules, the mucus on the nose actually helps to sort scent molecules. Doctor Brent Craven, from Pennsylvania State University, stated in Daily Mail: “We’ve shown that this sorting out of the different odorants before they even get to the receptors is also important”.

How does the Canine Olfactory System work?
Scent molecules are inhaled through the nose, and first sorted in the mucus covering the nose. When a dog flares his nostrils to sniff, the shape of the nostril openings change, and thus redirecting air into the upper part of the snout. This is where most of the olfactory sensory cells are located. These olfactory neurons have mucus-covered cilia (which are like little hairs) that reach into the nasal cavity. When scent molecules hit these cilia, the cell is stimulated, sending a signal along tiny nerves (or axons) which form olfactory nerves, and these congregate in the olfactory bulb. Next, the signals are carried from the olfactory bulb to the brain, which interprets them as smells.

This all sounds rather complicated, but to a dog it is no different than how we use our eye sight to determine things about our surroundings. Just like how we can look at a cluttered desk full of different objects and point out which one is a pencil, using our eyes, dogs use their nose to determine different scents amongst a clutter of other scents.



What else contributes to a dogs sense of smell?
Although it is still not fully understood, pigment seems to play a role in olfactory. The olfactory epithelium is pigmented, and its depth of colour seems to correlate with its sensitivity. It is light yellow in humans, and dark yellow or brown in dogs.

Pigmentations seems to also play a role in a dogs olfactory system. The olfactory epithelium is pigmented, and its depth of colour seems to correlate with its sensitivity. For example, in humans it is a light yellow while in dogs it is a dark yellow or brown. It has also been observed that light-coloured dogs have a less acute sense of smell than darker ones, and that albino animals have no sense of smell at all.

The anatomy of a dogs muzzle and nose play a big part in why they seem to have this “super sense”. It’s bony framework greatly influences the dogs smelling ability. Dogs with longer muzzles are better at scenting than shorter muzzled, or flat-faced dogs, most likely because they have more space for more olfactory receptors. Regardless of whether or not the dog has a short muzzle or long, the dogs nose is still a powerful tool.

Nostrils on dogs are highly mobile which gives them the advantage of determining the directions which scents are coming from. When a dog sniffs, incoming odor-laden air is directed onto the olfactory membrane over a structure called the “subethmoidal shelf” (this structure is not seen in humans). This shelf serves to accumulate and hold odor molecules in the nose as air is exhaled. The nasal mucous traps these molecules. This mucous is also produced in much higher quantities in dogs than in humans.

How much greater is dogs nose compared to mans?
How much greater a dogs nose is compared to mans is still quite unknown, especially since no two dogs have the same scenting capabilities. These capabilities vary between short and long nosed, different breeds, and individuals among different breeds. However, it is estimated that canines can smell somewhere between 10% and 100% better than humans.

Different breeds have different variations of receptor cells. For example, a Dachshund has approximately 125 million receptor cells, a Fox Terrier has approximately 147 million receptor cells, and a German Shepherd Dog has approximately 225 million receptor cells. The more the receptor cells, the greater the dogs ability is to detect and differentiate between different scents. Dogs with more receptor cells can also track for longer period of time (they can hold the scent for longer).