Upright and standing tall, folded or curled, cat ears come in a variety of sizes and shapes. Despite dramatic variations in appearance between some breeds, all cat ears function the same way. Ears can be the difference between winning a cat show or being able to dart away from danger. The ears are a component of the cosmetic appearance of a cat but they are also an important part of feline communication. Ear position lets you know if your cat is happy, scared, or mad. Ears provide a channel for hearing and function in balance, which are two very important senses in the animal world. Many owners think that their cat has a hearing problem when he does not come or perform on command. Unfortunately, this is seldom the case. I think the truth is that most cats have a very selective sense of hearing!
The anatomy of the ear is complicated, and the way it functions is amazing. The precise interactions involved occur in milliseconds. Hearing is a basic sense, but the components are far from basic. Balance and equilibrium are considered reflexes. The brain processes the information it receives from the ears and reacts without conscious thought ever occurring.
The ear is composed of three distinct areas: the external ear, the middle ear, and the inner ear. Most cat owners are familiar with the external ear. The pinnas are the skin and cartilage that protrude from the surface of the head, and what most owners consider to be the “ear”. The pinna conducts sound down into the external ear canal. The ear canal leads to the ear drum or tympanic membrane. The tympanum is the beginning of the middle ear.
The middle ear is encased in bone and delivers signals to the inner ear. Within this bone is a cavity that holds small bones (auditory ossicles) that connect the vestibular window. The vestibular system is responsible for balance. The inner ear is the termination of nerves that are components of hearing and equilibrium. It creates transmissions to the brain with information from fluid filled chambers called the cochlea and vestibular labyrinths. The brain processes these signals and is able to recognize sounds and balance. Any change in head or body position causes transmission of impulses to the brain that stimulate muscular reflexes to restore the body to a normal position.
Volume, pitch, and tone are components of sound that a cat can recognize. The actual receptors for sound are special hairs lining the basilar membrane of the organ of Corti in the cochlea. When the hairs are stimulated they evoke electrical impulses which travel to the brain. Through training and experience, the brain associates different sounds with different meanings. What may startle an older cat may not affect a young cat.
Assessing the hearing abilities of a cat is difficult. The only definitive diagnostic tool is the electroencephalograph, which measures brain waves in response to sound stimuli. This testing is performed under anesthesia and is only available through certain veterinary specialists. It is specifically called brain stem auditory evoked response testing. Most veterinary practitioners rely on less scientific testing, such as the cat’s response to a loud noise. Hearing is more important to a cat that spends time outside. Good hearing alerts a cat to cars and other animals that can pose threats. Deaf cats are at risk when let outside.
Loss of hearing in cats can be the result of a variety of problems. Trauma to the head or ear canal can impair hearing or cause complete deafness. Aging changes can decrease hearing and progress to deafness in geriatric cats. Tumors in the ear or brain can affect hearing abilities. Prolonged administration of certain antibiotics can cause hearing loss by damaging the hairs in the organ of Corti. Ear infections can cause permanent damage to the tympanic membrane, middle or inner ear. The most common cause of chemicals destroying hearing (ototoxicity) is the improper application of ear cleaners or mite killing products into ear canals with ruptured ear drums.
Deafness in cats can be a congenital abnormality. Developmental problems during gestation can lead to improper formation of ear structures. White cats, especially those with blue eyes, have a higher likelihood of deafness. This is because of genetic defects that cause numerous cochlear abnormalities.
At this time, hearing aids are not available for cats. If you have a deaf cat, you need to protect it from outdoor dangers. These include other animals and cars. Deaf cats are easily startled, and in my experience can be more aggressive. They can be more defensive and protective since they’ve lost one of their important protective senses. Fortunately deaf cats can make good pets and live normal life spans. If you are unsure about your cat’s ability to hear, you should consult with your veterinarian.
Written by Dr. Wexler-Mitchell of The Cat Care Clinic in Orange, CA
Copyright © 2011 The Cat Care Clinic