The 5 senses of the dog: smell, sight, taste, hearing and touch

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 The smell

The dog's sense of smell is undoubtedly the most developed sense: it is between 30 and 40 times more developed than in humans. The olfactory mucosa is very developed and covers a very large surface with a significant number of olfactory receptors connected to the brain by nerves. It also has a vomeronasal organ, also called Jacobson's organ, which is very important in detecting pheromones. These are molecules with a chemical structure similar to that of hormones, which act as messages between dogs and even with other species.

Dogs can detect certain odors very finely. Through the sniffing mechanism, which consists of very short inspiration/expiration cycles, they are able to maximize the reception of molecules by bringing a large quantity of molecules to the receptors located in the nose.

The dog uses its sense of smell to find its way. It compensates for its poor eyesight by an increased scan of odors in its environment. It can recognize places without seeing them and find its way thanks to the odors encountered on its way.

His sense of smell also serves him in the search and selection of food. Before eating anything, a careful olfactory inspection is made by the dog to compensate for the small number of receptors present on his tongue. Finally, the dog uses odors to communicate with his peers. During walks, dogs sniff each other to get to know or recognize each other. These odors are also used during reproduction so that the male recognizes females in heat.

Their sense of smell is also of great use to dog squads, for example for detecting explosives, narcotics, or for finding people buried under avalanches or rubble during earthquakes.

In addition, very promising recent studies have been carried out on dogs for the detection of SARS-Cov2 (the virus responsible for Covid-19) or for the early detection of prostate cancer on urine samples. Other dogs are trained to help people with diabetes or epilepsy, for example, because they are able to detect seizures early and can therefore warn the beneficiary so that they can get to safety before the seizure occurs.

Finally, other leisure activities include dogs' highly developed sense of smell, such as searching for game when hunting or for truffles.

View

There is still a common misconception about dogs' vision: dogs see in black and white. Well, that's wrong! Of course, dogs don't see as well as we do, but they can detect a limited range of colors.

The retina is the structure at the back of the eye that receives light information. There are two types of cells: cones, which are used for color perception, and rods, which help with night vision and motion detection. The ratio of these two cell types is different from that of humans; dogs will therefore see fewer colors but will see better at night and see movement.

Another peculiarity is that dogs have a surface that reflects light on the retina, called "the carpet,"  which allows them to see better in the dark by amplifying the light that reaches the retina. This is why dogs have eyes that "glow" at night, like cats.

Finally, dogs have a wider field of vision than humans. In fact, their eyes are more lateral on their face, which allows them to have a much wider field of vision!

Taste

In dogs, the sense of taste is less developed. They have fewer taste buds than humans. They can recognize bitter, sour, sweet, and salty tastes, but the range of nuances that their taste buds can recognize is more limited. Before eating a food, smell therefore plays an essential role before deciding whether or not to ingest it. You will surely see your dog sniffing his food or a different food for a long time before putting it in his mouth.

Like us, some dogs are greedier than others. It is even suspected that this may be due to genetic factors in some breeds. For example, the POMC gene in Labradors is mutated, which changes their behavior and reduces satiety. As a result, they will be satiated much less quickly. This certainly predisposes them to obesity, but it is nevertheless an advantage in terms of training, thanks to the high level of motivation in a reward system.

Hearing

The dog has a hearing superior to that of man, both in terms of distance and in terms of range of sounds. In fact, it perceives ultrasounds, that is to say sounds that have a frequency greater than 20,000 hertz. It also perceives infrasounds, that is to say sounds whose frequencies are lower than 20 hertz.

This increased perception of sounds is explained in particular by the anatomy of the dog's ear, the latter having a large quantity of sensory cells in the inner ear at the level of the organ of Corti. These receptors make it possible to receive high-frequency sound waves.

Touch

Unlike humans, who only have the skin as an organ of touch, other organs are integrated into the dog's perception of touch. First of all, the dog's skin includes, like that of humans, thermoreceptors and mechanoreceptors, which ensure the perception of variations in pressure or temperature. The dog has the particularity of having a very developed platysma muscle that covers the surface of its trunk and which allows the hairs to stand on end or contract during pinching, for example.

The dog also has whiskers, which help it to find its way in space thanks to mechanoreceptors that bend under the effect of air movements or pressure and are integrated as information by the nervous system.

Our furballs do not have the same perception of their environment because their senses are not equal. The overall knowledge of the anatomy of the sense organs and its consequences allows us to better understand our dogs by observing them in their living environment and to question their behaviors when faced with external stimuli.

Bibliography

  • Courses at the National Veterinary School of Alfort on anatomy, physiology, and neurology
  • GRANDJEAN D. (2021) Olfactory Detection Dogs for COVID-19 Screening What's up to date? Journal of Animal Sciences and Livestock Production
  • GUEST C., HARRIS R., SFANOS KS, et al. (2021) Feasibility of integrating canine olfaction with chemical and microbial profiling of urine to detect lethal prostate cancer. PLOS ONE
  • University of British Columbia (2020) UBC Neuroanatomy. In neuroanatomy.ca [http://www.neuroanatomy.ca/]
  • ARANEDA RC, KINI AD, FIRESTEIN S. (2000) The molecular receptive range of an odorant receptor. Nature Neuroscience 3(12)

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