More so than sight, smell dictates a feline’s behavior and is one of the most important ways it receives feedback about its environment. A cat’s sense of smell is superior to any human’s. Felines have 200 million odor-sensitive receptors, much higher than the 5 million for humans. Even most dog breeds fall short to that number.
Cats are born with a great sense of smell. From the moment they are born, a kitten already has a highly developed sense of smell. This provides them the ability to distinguish their mother’s smell and locate its preferred nipple to nurse from even when their eyes are shut. Until their vision becomes a kitten’s main guide after 3 weeks of age, it relies on its olfactory, the medical term for the sense of smell, cues for navigation. Even then, felines rely on their olfactory senses in order to determine edible prey. It is known that cats with the inability to smell may refuse to eat. Cats with upper respiratory infections and have congested nasal cavities often lose their appetites.
Cats use their sense of smell to smell food and guide them to prey, locate a mate, recognize enemies and dangers, establish territorial lines, and discover where an individual has been.
Anatomy of the Nose
The visible nose of a feline comes in a variety of color and is unique to each individual. The color of a cat’s nose is directly related to the color of its fur. If they have solid color pelts, so will their noses. If multicolored, it is possible for its nose to be multicolored as well. And like a human’s fingerprints, every cat’s nose has a unique pattern of bumps and ridges. The outer nose protects the nasal cavity from weather and foreign bodies as scents waft towards the cat’s face.
Past the nostril openings, also known as nares, is the nasal planum (the external bridge), the nasal cavities, and the sinuses. There are two nasal cavities, separated by the nasal septum, a bone and cartilage structure. The floor of the nasal cavities is the bony hard palate, which continues toward the pharynx and becomes the soft palate-nasolacrimal duct, the drainage path for tears.
As the passing air is cleaned, moistened, and warmed by the nasal cavity, it passes over the maxilloturbinals at the back of the cavity. Turbinates are the vascular cartilaginous projections that are shaped in a honeycomb structure. Within the structure are mucosa-olfactory nerves to the brain’s olfactory bulb. These nerve endings are coated in a thin protective film of mucus which traps the air molecules that make up the smell. They are connected together in bundles between 10 to 100 of the same kind of receptor before transmitting their information to the brain. Depending on which type of receptor is being stimulated and by how much in comparison with other types of receptors, the brain can deduce the character of each odor.
Olfactory Apparatus: The Vomeronasal Organ
The vomeronasal organ (VNO), also known as the Jacobson’s organ, is present in many animals and has been studied for its importance in the role of reproduction and social behavior. However, the genes essential for VNO function are non-functional in humans. Most studies agree that the organ regresses during fetal development.
The VNO is the first stage of the accessory olfactory system and contains sensory neurons that detect chemical stimuli. Also known as pheromones, the stimuli are chemical messengers that carry information between individuals of the same species.
The opening to the VNO is the papilla behind the upper incisor teeth which opens up to two nasopalatine canals. The canals will run from the roof of the cat’s mouth to the nostrils. Connected halfway up each one of these tubes is a sac that contains its own VNO filled with chemical receptors and fluids so that odors can be dissolved in saliva to be detected. Cats contain at least 30 different kinds of receptors, more than the nine a dog has, thus detecting and analyzing a wider range than a dog. The ducts connecting the VNO to the canal are only about 1/100 of an inch wide, so thin that the odors must be pumped in and out of the sacs by a dedicated set of tiny muscles. This gives the cat precise control over when it uses the VNO, unlike the nose which is always collecting sensory information.
Each of the receptor cells are connected to their own area of the brain known as the accessory olfactory bulb and to the amygdala region of the hypothalamus, a region of the brain associated with sexual, social, and feeding activities.
In order to utilize the Jacobson’s organ, the cat performs the Flehmen response. The flehmen behavior is used when the cat draws its lips back, wrinkles its nose, and opens its mouth partially for inhalation. This behavior allows the odors to enter the oral canals and reach the VNO. Cats may also taste the object that is being analysed by licking it. This further aids the cat when detecting scents.
This type of facial contortion is used exclusively in social situation. Although intact, meaning not neutered, males most commonly use the Flehmen response during courtship, both sexes have been recorded of doing it. It is seen in kitten as young as two months of age.
Featured Image Via Wild Eye Showing a Lion’s Flehman Response
References + For More Reading
Cat Sense by John Bradshaw
Smithsonian’s Answer Book: Cats by John Seidensticker
Eyewitness Companion: Cat by Dr. Bruce Fogle