Music to My Ears: Feline Hearing (and Balance)

“Hearing is the cat’s second most important sense, which is one of the reasons blind cats can get around well.” – Dr. Weigner

A superior ability to detect sound helps the cat not only in locating prey but also detecting predators and navigating its environment. This skill is attributed to a cat’s ears, the paired receptor organs designed for the special senses of hearing and maintaining balance. The ears are located on both sides of the head, sitting above and behind the eyes. The external portion is identified as the pinnae but also consists of the middle and inner ear which are located internally.

Cats are very sensitive, with a range of hearing both above and below the range of frequencies that can be detected by humans. They can hear better than people and even better than most dogs. They are also able to accurately pinpoint the source of a sound. A cat up to 3 feet away from the origin of a sound can pinpoint its location to within a few inches in a mere 6/100th of a second. Not only are they accurate, they can also hear sounds at far greater distances – four or five times farther away than what humans can hear.

feline-primary-field-of-hearing

The two main functions of the ear are to detect sound and allow for hearing as well as to maintain balance.

Sound enters the external ear canal as sound waves. As these waves strike the eardrum, it begins to vibrate and the three small bones of the middle amplify the sound vibration. It then moves to the cochlea, the snail shaped portion of the inner ear, transforming the vibrations into nerve signals and are transmitted to the brain for interpretation.

To maintain balance, the three semicircular canals of the inner ear are orientated at right angles to each other. When the head turns, the resulting movement of fluid in these canals allows the brain to detect which way and how much the head is turning. Another part of the inner ear responds to gravity and sends information to the brain when the head is held still, in a stationary position.

Anatomy

Each ear is divided anatomically and functionally into regions called the external (outer) ear, the middle ear and the inner ear.

The external part of the ear is called the pinnae and is made up of 30 muscles compared to a human’s six. This allows the pinnae to move forward, backward, and down (approximately 180 degrees) to better pick up sounds to accurately understand where the source of the sound is. It is covered by skin, and the outer or posterior aspect is covered by short and sparse fur.

The inner or anterior part of the pinnae is naked except for numerous long hairs which protect the inner ear by straining out foreign bodies that come in contact with them. The pinnae extends to the external ear canal, which is deeper and more tapered than in people, creating a better funnel to carry sound to the eardrum. This deeper canal is subject to buildup of dirt and wax that can lead to inflammation and secondary infection, although to a lesser degree than in dogs.

The small purse-like flap of skin on the posterior and lower edge of the pinnae is also credited with increasing sensitivity to sound, but whether this flap actually has this function is questionable.

cat_covers_ears
Via Cat Talk 101

Next are the middle and inner ear, which share similarities with the human ear in both structure and function. However, a cat’s ear canals are practically immune  to seasickness or carsickness, an ailment that torments a good percentage of people and canines, but cannot be explained due to a cat’s close biological similarities to them.

The middle ear includes the eardrum and the bony tympanic cavity (osseous bulla), which lies just past the ear drum. It is connected to the pharynx, the back of the throat, by the auditory or eustachian tube.This connection allows air from the pharynx to pass in and out of the middle ear in order to keep the air pressure within the middle ear normal.  

Within the cavity are the auditory ossicles which are the three smallest bones in the body that vibrate when stimulated by sound waves. These ossicles are named the malleus, stapes, and incus. They are also commonly known as the hammer, the stirrup, and the anvil respectively due to their resemblance to those objects. The three bones form a chain across the middle ear and will connect to the inner ear through the oval window, which lies against the stapes bone.

ddc_cat_inside_ear
Via Merck Vet Manual

The inner ear is actually located within the petrous temporal bone of the skull and consists of two parts. It is the most complex structure in the ear’s anatomy, containing the cochlea (the organ of hearing) as well as the vestibular system (the organ of balance). The inner ear, while the rest are still developing, is already functional in the 54 day old cat fetus, six days before birth.

The cochlea is a spiral tube in shape and contains the nerves that transmit the electrical impulses to the cerebrum, the part of the brain responsible for hearing, through the two branches of the 8th cranial nerve, the vestibulocochlear nerve. Complete destruction of the cochlea in one ear results in a hearing loss of 3 to 5 decibels. Pathological changes in the cochlea due to genetics are usually the cause of deafness in blue-eyed white cats. These cats usually compensates for their lack of hearing with extreme sensitivity to vibrations.

Unlike the cochlea, the vestibular system, which is made up of the vestibule and semicircular canals, is responsible for maintaining balance or equilibrium. These tissues are also supplied by the vestibulocochlear nerve, which will transmit electrical impulses related to both sound and balance back.

Range of Hearing

A cat’s range of hearing is extensive. Its best hearing is around 8 kilohertz but continues to maintain excellent hearing to around 40 kilohertz. This is because the eardrum is divided into two interconnecting compartments, thereby increasing the range of frequencies over which the eardrum will vibrate. They can accurately and effortlessly ascertain the direction and depth of a noise above or immediately behind them. This is attributed to their mobile pinnae, as cats are able to point their ears to and away from the source of sound for confirmation.

Cats can hear not only the same full range of frequencies as humans but also almost two octaves higher than ours, which we refer to as ultrasound (greater than 20 kilohertz). A cat can hear ultrasonic frequencies to about 60-65 kilohertz. This means that cats can hear the ultrasonic pulses bats use to orient themselves while flying in the dark and the higher pitched squeaks of mice and other small rodents.

hearingranges_chart
Via Cat Talk 101

They can also hear a lower range that humans can’t detect called infrasonic (less than 2 kilohertz) based on the size of its head. Usually, as the feline species get bigger, auditory sensitivity shifts toward lower frequencies. In fact, humans can’t hear all of a lion’s roar as a part of the communication is infrasonic. This is possible because of the exceptionally large resonating chamber behind the eardrum.

Many natural occurrences such as avalanches, earthquakes, volcanoes, and severe weather produce infrasonic sound. It is possible that cats can detect these frequencies, causing them to be aware much earlier than humans during these events. Low frequency comparisons are often difficult to make because of our inability to devise adequate tests for such measurements (as we are unable to hear below our limit).

A cat’s hearing is superior to a human’s in all ways except one: the ability to distinguish minor differences between sounds in pitch and intensity. If it was possible to train a cat to sing, it couldn’t sing in tune. But, humans can. We can tell similar sounds apart, probably an adaptation in our use of speech. Our ability to recognize subtle intricacies of intonations indicate the emotional content of what we are hearing.

Deafness

Cats, like humans, can experience hearing problems or even total deafness due to disease, infections, outer-ear trauma, inner-ear damage (from excessively loud noises) or simply old age.

The cat’s ability to detect high frequencies particularly declines as the eardrum thickens with age. This condition not only affects the cat’s hunting skills; it also can compromise the feline’s ability to heed noises signaling danger.

In domestic cats, however, deafness is most commonly hereditary. Although inherited deafness has not been genetically related to specific breeds, the dominant gene responsible for producing white hair is sometimes associated with inner-ear abnormalities that often lead to deafness.

Incidences are highest in white cats with blue eyes; white cats with eyes of different colors are often deaf only in the ear on the blue-eyed side.

The Organ of Balance

6885ec4c57940019fd46a2c162abac19Housed deep in the cat’s inner ear is the vestibular apparatus which is responsible for its remarkable sense of balance. This sense organ’s tiny chambers and canals are lined with millions of sensitive hairs and contain fluid and minute floating crystals. When the cat moves, the delicate hairs detect the movement of the fluid and crystals and will send messages to the brain on the body’s position. This gives the brain accurate readings so that it can send the signals for the necessary muscles to compensate, thus achieving a “cat-like” perfect sense of balance. This mechanism is very similar to the instrument used in airplanes called the “artificial horizon” or “altitude indicator” which tells the pilot the position of the plane’s wings in relation to the horizon.

When a cat loses its balance, the vestibular apparatus is key to right itself. It helps the cat register which direction is up and triggers the “righting” reflex that cats rely on to turn themselves in midair, adjusting the orientation of the body so that they land squarely on all four feet. However, recent studies disprove the old wife’s tale that cats will always land on their feet. It seems that falls from a shorter distance to the ground are actually more dangerous in terms of injury to the cat than falls from a longer distance to the ground as there is less reaction time to properly react.

Along with this organ, balance is maintained using the tail, which acts as a counterbalance. The vestibular apparatus, along with the tail, enables the cat to perform its remarkable signature acrobatics. They enable the cat to jump with an almost military-like precision, reaching into the air to catch flying prey, or moving from one spot to another with ease.

The Manx, a tailless breed, is thought to have an especially sensitive vestibular apparatus to compensate for the lack of the tail’s counterbalancing properties.

References + For More Reading

Cat Sense by John Bradshaw

Smithsonian’s Answer Book: Cats by John Seidensticker

Eyewitness Companion: Cat by Dr. Bruce Fogle

Natural History of Cats by Claire Necker

Cat Ears & Hearing

Feline Ear Disorders

Deafness

Cats’ Sense of Hearing

Structure and Function of the Ear in Cats

Ear Infections in Cats: Causes, Treatment, and Prevention

Study: Hearing Range of a Domestic Cat

Cats Ears

About Hearing in Cats

Structure and Function of the Ear in Cats

Ear Structure and Function in Cats

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