How Does a Cat Purr Physically?

Physical Process

• The purr sound is continually generated during both the inhale and exhale processes of the common house cat. According to Associate Professor Vanessa Barrs at the University of Sydney, the sound resonates from the vibration of throat muscles located along the length of the throat cavity. These laryngeal muscles control the glottis or vocal chords of the cat. When a cat is purring, these muscles tighten to create space between the chords, which results in the unique sound created as air passes through in either direction. The diaphragm also plays an indirect role in the generation of purring sounds as it regulates inhalation and exhalation, but it is not involved in the vocal chords themselves.

Meaning

• In the first weeks of life, a kitten's purr is thought to signify its well-being to the mother cat. In mature cats, purring is thought to symbolize general contentment, whether as a result of attention from a person or a fulfilling meal. However, according to Associate Professor Leslie A. Lyons of the University of California, purring often also takes place during physically stressful occasions, like extreme pain or fear. Barrs suggests that purring may be a comfort mechanism.

Physical Effects

• Purring may help cats with everything from gaining the attention and sympathy of their human hosts to repairing all manner of internal injury. Cats may purr to prevent blood clots and pooling during extensive and frequent rests, much the way humans can have these problems during long periods in a seated position. According to Elizabeth Von Muggenthaler, purring may also be a method by which cats heal any skeletal or muscular illness or defect they might be experiencing. Dr. T.F. Cook's observations from the 1970s suggest that cats may use purring as a treatment for breathing issues like dyspnea.

  At this point, there remains no definitive data on the direct physical effects of purring, in large part because a non-invasive method for testing living cats has not yet been developed. Most likely, purring is a vocal signal that may also provide something of an internal massage for the cat, which may have beneficial health effects.

Cause

• According to a 1991 study by Frazer-Sisson, et al., titled How Cats Purr, purring is caused by a neural function also unique to domestic cats which directly controls the laryngeal muscles. Vanessa Barrs believes that as a physical function, purring is involuntary and results from an automatic trigger in the cat's brain. While the frequency of the sound and the constriction of the throat muscles is involuntary, control over the act or cessation of purring remains voluntary.

Wild Cats

• While domestic cats are the only species that purrs during both inhalation and exhalation, many wild cats also exhibit some for of purring during exhalation only, according to Barrs. Barrs says that the list of big cats who purr regularly includes jaguars, panthers, leopards, tigers, lions and wildcats. All cats are capable of some form of purring but some do so more than others. Cheetahs, for instance, do not have the capacity to roar and instead engage only in loud purring, according to the National Geographic Big Cats Initiative.