What are exactly senses and how do they relate to dogs? If we look at our reference book "Clinical Anatomy & Physiology for Veterinary Technicians, p. 269:" it says that senses are "extensions of the central nervous system" that allow it to monitor what's going on inside and outside of the dog's body. Generally, when an internal or external stimulus is detected by the dog's sensory receptors, a nerve impulse travels to the dog's central nervous system and then it's interpreted as a sensation that may generate a response. How many senses do dogs have though? So here's our Tuesday Trivia question for today:
How many senses do dogs have?
A: Less than 5
C: More than 5
And the answer is......
Answer: if you answered A, which is less than 5, you have missed out several important senses. If you answered B and said 5, you may likely think you got it right, as traditionally most of us grew up knowing that there are 5 main senses, but there are actually many more! So the correct answer is C, more than 5. Let's take a closer look at them, shall we?
A Dog's Five Special Senses
These are for a good part the senses we are mostly accustomed to, the traditional ones we grew up knowing from studying them in classes. What these special senses have in common is that the sensory organs are located in the dog's head. Even though these senses are the ones we most commonly think of, by limiting ourselves to these, we fail to give our dog's bodies full credit for all of the amazing things they're capable of doing. Here's a quick rundown of them:
Sense of Taste: also known as the gustatory sense, your dog has several sensory receptors in his dog's mouth which are commonly known as "taste buds." Most of these are located on the tongue, but some are also found in the lining of the dog's mouth and throat. When these receptors are stimulated, they generate nerve impulses to the brain which are interpreted as taste.
Sense of Smell: also known as the olfactory sense, your dog has several sensory receptors in his nose that generate nerve impulses to the brain and are interpreted as odors. A dog's sense of smell is surely remarkable compared to ours and plays an important role in his perception of the world. If you're guilty of yanking on your dog's collar the moment he stops to sniff the fire hydrant, it's time to start seeing things more from your dog's perspective. Next time, as you walk towards the hydrant, ask your dog to heel a few steps and then reward him by telling him to "go sniff!" the fire hydrant. Your dog will be grateful for that and you can take a moment to admire this amazing sense.
Sense of Hearing: also known as the auditory sense, your dog's hearing system converts vibrations of air molecules into nerve impulses that are interpreted by the brain as sounds. Does your dog sometimes barks at night and you can't find a good reason why? Most likely, your dog has a good reason to bark as he can hear sounds that our ears cannot detect. If he does it quite often, it's not a bad idea to check your attic, deck, basement or yard for any unwanted critters.
Sense of Vision: when it comes to vision, dogs have less visual acuity, color and depth perception compared to us humans, but they're good at sensing movement even in dim light. When the photoreceptors of a dog's eyes detect a stimulus, they generate nerve impulses that are interpreted by the brain as images.
Sense of Equilibrium: we're not used to including this sense with the usual ones we're most accustomed to, but it's a sense and and as such deserves its spot among the other dog's senses that originate from the dog's head. We often take this sense for granted, but it's thanks to this sense that our dogs are capable of maintaining their balance. The equilibrium receptors in this case are found in the dog's inner ear and they collaborate with the eyes and several other sensors called proprioceptors that provide information about the dog's position in space.
As the name implies, general senses are senses that are distributed throughout our dog's bodies other than being restricted to the head. When we think about a dog's senses, we often think about the sensory organs that we are used to seeing on our dog's bodies such as the dog's nose, ears and eyes, but that's just half of the story as there are several more! Several fall under the visceral category, meaning that they are interior, within the dog's body. Here's a quick rundown of them.
Sense of touch: also known as tactile sense, this sense tells the dog that something is in contact with the surface of his body. Special touch receptors located on the dog's skin inform the dog's brain about several sensations such as pressure, vibrations, and texture. The skin is the dog's largest organ and it's meant to protect his internal body from potential dangers of the external world.
Sense of Temperature: dogs also have several temperature receptors which are meant to inform the dog's central nervous system about the body's temperature so the body can make adjustments to return it within normal range. The dog's temperature control system may therefore attempt to correct any conditions of hypothermia (low body temperature) or hyperthermia (high body temperature).
Sense of Pain: dogs have several pain receptors, known as nociceptors, which are located on the surface of the body and inside of the body. These pain receptors are found scattered almost everywhere on the dog's body so the central nervous system can be alerted and measures can be taken to protect it. Sadly for many years, pain perception in dogs was underestimated, but nowadays a better understanding of ways dogs manifest pain proves they feel pain just as we do.
Sense of Inner Body: also referred to as "visceral sensations" under this category are found some miscellaneous senses of things happening internally. A deficiency of water elicits the sensation of hunger. A deficiency of nutrients elicits the sensation of hunger. Internal organs that are hollow have stretch receptors meant to inform about a sensation of fullness (think a full bladder eliciting a need to urinate) or pain (think the a bubble of gas in the intestine or the pain of a urinary stone).
Sense of Proprioception: we may not be too familiar with our dog'sproprioception sense, but our veterinarian certainly is and even more are veterinarians specializing in neurology. Dogs have several stretch receptors located in their muscles, tendons, joints and ligaments that are meant to inform the central nervous system about their whereabouts, including position, contraction of muscles, tension on ligaments etc.
In other words, they help your dog know exactly where his body parts are, relative to their other body parts. When neurologists must evaluate dogs for neurological problems they'll often lift the dog's foot so that it's upside down and evaluate how long it takes for the dog's nervous system to detect the abnormality and adjust the foot's position.
So here you have it, 10 senses, which include 5 special senses and 5 general senses. There may be even more though if you talk to a neurologist. Quite amazing, huh? But wait, this isn't limited to only dogs! For the human version of this article read "How Many Senses Do You Really Have?" And just between us, let's not forget about "sense of humor" and "common sense"! Just joking of course, haha!
Clinical Anatomy & Physiology for Veterinary Technicians, Thomas Colville DVM MSc, Joanna M. Bassert, VMD, Mosby 2002