The Basics of Canine Senses
A dog’s nervous and sensory systems are essential to his health and well-being. Perceptions and reactions to his environment are dependent on his senses; movement is controlled through the central nervous system (the brain and spinal cord); and the endocrine system (the hormone-producing glands) controls his patterns of behaviour.
Canine vision is inferior to human during the day, but is superior at night. Dogs do see colours, but not as distinctly as humans (in pastel as opposed to strong colours), and their peripheral vision is better than ours. In addition to the upper and lower eyelids, there is a third eyelid – the nictitating membrane (haw), which is comprised of a thin sheet of pale tissue tucked away in the corner of the eye. Its function is to help remove dust and dirt from the surface of the eye (cornea) by moving across it during any inward movement, and also to help keep the eyeball moist and lubricated.
A dog’s hearing is vastly superior to that of a human and he is, therefore, more sensitive to sounds than we are – especially those at high frequencies which we cannot hear (hence the use of ‘silent’ dog whistles). A dog’s mobile ears help to pinpoint the source of a sound, since they can be directed towards it.
A dog’s primary sense is his sense of smell, as it is essential in relation to his sex life and hunting for food and water. The area in a dog’s nose for detecting scent is nearly 37 times larger than that in humans, and is approximately 100 times more powerful than a human’s. The parts of the brain that process signals coming in from the nose are far greater in size and complexity in a dog than are the corresponding parts of the human brain.
A special organ in the roof of the mouth – the vomeronasal (or Jacobson’s) organ -‘tastes’ certain smells (such as that exuded by a bitch in season) to help the dog analyse and react to them faster. When the dog is using this organ, he will draw in mouthfuls of air and appear to be ‘tasting’ it.
When two dogs meet they will usually smell each other’s face and then their inguinal regions. Scent plays a significant part in territory. When a male dog marks a prominent object with urine, he is deliberately masking the smell of dogs that have recently passed by, and thereby stamping his claim as ‘top dog’ in that territory. Faeces are also used as scent markers, with the anal glands discharging a foul-smelling substance unique to that dog.
Whereas humans have taste buds, situated on the tongue, that differentiate between sweet, sour, salty and bitter tastes, the canine sense of taste is thought not to be as well developed – only about one-sixth as sensitive as that of humans.
Dogs use their noses, mouths and paws to examine objects, after first checking them using their primary sense, smell. The skin is the main touch receptor, and different breeds and types of dogs are more touch-sensitive than others. Dogs that have not been well handled since puppyhood tend to shy away from being touched in sensitive areas, such as the feet, mouth, head, ears, between the hind legs and tails – these are the areas on a dog’s body that are vulnerable if attacked.