Stolley Park
Veterinary Hospital

3020 W. Stolley Park Road  Grand Island, Nebraska  68801  

October Newsletter

The Mystery of a Cat's Purr

For centuries humans have adored cats and shared their lives with these fascinating creatures. Yet in this technological age of voicemail, e-mail, cyberspace and text messages, humans have yet to discover and understand the mystery of how cats purr. Any cat lover knows why and when their cat purrs, but to explain how a cat purrs is more difficult.

There are different theories about how purring is generated. Some believe purring is caused by vibration from air movement across the soft palate located in the back of the throat. Others speculate that a purring sound is created through turbulence in the blood vessels passing through the chest across the diaphragm (the muscle that controls breathing). But most people feel that purring originates in the larynx. The larynx is part of the respiratory tract and serves as a passageway for air in and out of the lungs. It is a cartilaginous structure surrounded by several muscles. Moving air through the larynx creates all other vocalizations made by animals. It seems most plausible that this would be the case for purring as well.

The sound of a purr is generated by alterations in air pressure. Electrical impulses emitted from the brain stimulate the muscles of the larynx, causing them to rapidly contract and relax at approximately 20-30 times per second. The result of this rapid muscle stimulation creates fluctuations in air pressure in the larynx. The rapid increase and decrease in air pressure produces the sound we hear as a purr. If one listens closely to a purring cat, an audible change in intensity can be heard as a cat breathes.
Members of the feline family are the only animals that possess this unique gift. The ability of a cat to purr does vary within this family. Not all cats can purr during inhalation and exhalation, and the intensity of the sound varies among species. Cats that can purr include: domestic cats, puma, mountain lions, leopards, cheetahs, lions and tigers. Raccoons, black bear cubs and hyenas have also demonstratedsome ability to purr.

Most people believe that purring is used for communication purposes. Nursing queens have been observed purring and kittens can purr by the second day of life. It is also likely that purring has a calming effect on the cat itself. Many severely ill or injured cats continue to purr. Some research has been done to support that purring aids in the ability of the feline to heal because of the frequency of the sound made.

In summary, cats purr when they are content, as a means to communicate, and possibly to comfort themselves. The sound originates from the larynx through rapid muscle stimulation and air pressure fluctuation. Since felines are the only creatures that can purr, we still do not completely understand the phenomenon. Will there ever be an answer to the question: How does a cat purr? The world may never know!

Submitted by: Jennifer McCartney, DVM