By Matt Soniak
Cats are fascinating creatures, and they’re built with some pretty amazing functions. As we’ve already pointed out, their “software” is pretty advanced, and they’re not lacking for cool hardware, either. A lot of attention gets paid to animals’ senses of smell and sight and their noses and eyes, but cats’ ears and hearing deserve a little praise, too. Here are 10 things you might not know about your cat’s ears and what they can do.
1. Cats’ ears are pretty similar to those of other mammals and share the same three structural areas: the outer ear, middle ear, and inner ear. The outer ear is made up of the pinna (that’s the external triangular part you can see on top of their heads, and what we usually think of when we talk about their ears) and the ear canal. The pinna’s job is to capture sound waves and funnel them down the ear canal to the middle ear. Cats’ pinnae are mobile, and they can turn and move them independently. “Cats have a lot of muscle control over their ear,” says Dr. George Strain, a neuroscientist at Louisiana State University’s School of Veterinary Medicine. “They can actually use it like a radar unit and turn it toward the source of sound and increase their hearing sensitivity by 15 to 20 percent.”
The middle ear contains the eardrum and tiny bones called ossicles, which vibrate in response to sound waves and transmit those vibrations to the inner ear. In the inner ear, sensory cells in the organ of Corti respond to the vibrations by moving and bending, which sends electrical signals through the auditory nerve to the brain for processing.
The inner ear also contains the vestibular system, which helps provide a sense of balance and spatial orientation. Its shared location and connectivity to the sensory parts of the inner ear mean that an inner ear infection can affect both hearing and vestibular function, Strain says. “As a result, [a cat with an inner ear infection] may exhibit signs like a head tilt or a curvature of the body toward the side where the infection is.”
2. For all their similarities to other mammalian ears, cat ears do have some anatomical differences, including one that can frustrate veterinarians. “One of the things that we struggle with in patients who have middle ear infections is that cats have a septum, like a bony shelf, that separates their middle ear into two compartments,” says Dr. Christine Cain, the section chief of dermatology and allergy at the University of Pennsylvania School of Veterinary Medicine. “That can make it really difficult for us to resolve their middle ear infections because there’s a compartment that you just can’t get to very easily.”
3. You might have noticed cats have folds of skin forming what look like small slits on the outer bases of their pinnae. These little structures are formally called the cutaneous marginal pouches, but are more commonly known as Henry’s pockets. Veterinarians are unsure what purpose the pockets serve, if any.
Henry’s pocket is a pretty great anatomical term, and there’s another one for the tufts of fur that grow on the interior of cat’s pinnae—they’re called “ear furnishings” by cat fanciers and breeders.
4. Most cat owners can tell you, anecdotally, that their pet has a very good sense of hearing. But just how good is it? “Cats hear lower frequencies and higher frequencies than dogs and people do,” Strain says. A cat’s hearing range is approximately 45hz to 64khz, compared to 67hz to 45khz in dogs. While the range of human hearing is usually pegged at 20hz to 20khz, Strain says 64hz to 23khz is a better representation.
“Among domestic animals, cats have some of the best hearing,” he says. “It helps them in that they’re predators by nature—being able to hear a wider range of sounds helps them detect a wider range of prey species, and gives them a chance of hearing and avoiding their own predators.”
5. White cats with blue eyes have higher than normal incidences of congenital deafness due to genetic anomalies that result in the degeneration of some of the important sensory parts of the ear. “The gene that produces white hair and skin does so by suppressing pigment cells,” Strain explains, including those in the tissue of the inner ear. If those cells don’t function, he says, the tissue degenerates and the sensory cells involved in hearing die, leading to deafness.
6. Some cats have four ears (or at least four outer ears, with extra pinnae behind their normal pinnae). The additional ears are the result of a genetic mutation. “They also have some other abnormalities,” Cain says. “Their eyes are smaller and they have a little bit of an underbite, too.”
7. Cats’ ear canals have a self-cleaning mechanism, Cain says, and they don’t need your help keeping their ears clean. In fact, trying to clean a cat’s ears can cause ear problems to develop. “They’re sensitive creatures and susceptible to developing things like irritant reactions when we put things into their ears,” Cain says. “Unless your cat has an ear problem, for which you should go to your veterinarian, I wouldn’t do a lot of cleaning at home. Don't try to fix it if it’s not broken.”
8. Cats are an altricial species, which means that for some time after birth, they’re relatively immobile and not all of their sensory systems are working at their full potential. Strain says cats are born with their ear canals sealed and their auditory systems immature. “They respond to sounds as soon as the ear canal opens, and their hearing threshold will get better—that is, they can hear softer and softer sounds—in the several weeks after that,” he says.
9. A cat’s ear temperature can help you tell if he is stressed out. Cats’ responses to fear and stress include increased adrenaline and other physiological changes that lead to energy generation in the body. Part of that energy is released as heat, increasing a cat’s body temperature in several areas. Scientists have found that the temperature of a cat’s right ear (but not the left ear) is related to the level of certain hormones released in response to stress, and could be a reliable indicator of psychological stress.
10. Giving a hearing test to a cat is sometimes tricky, but it can be done. Behavioral tests where veterinarians make a noise and look for responses have several problems, Strain says. They can’t detect unilateral deafness, for example, and it’s not uncommon for cats to be stressed out and unresponsive during the tests.
“The most objective test we have available to us is the BAER test, which stands for brainstem auditory evoked response,” Strain says. In these tests, he explains, electrodes are placed under the skin on the top of a cat’s head and in front of each ear. A sound is then played into each ear, and the electrodes detect electrical activity in the auditory pathway.
“It’s like a TV antennae picking up a signal deep in the brain,” he says. A series of peaks in activity indicates the ear heard the noise, while a lack of activity peaks suggests the ear is deaf.
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