How Do Cats Purr?

Ever had a cat curl up next to you and start purring? Their little motor that seems to run all the time is one of the things we love about cats. They seem to be able to purr at will, and sometimes the purring can go on for hours. Just how do they do it?

A cat purring on your lap is one of the best things ever for cat people.
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Cat vocalizations

Purring is just one of the many cat vocalizations. Purring is different than meowing, which is the other most common of the cat vocalizations. The classic meow can only be done on exhalation while a purr is different in that they can do it across the entire breath cycle of inhale and exhale.

Some other common cat vocalizations anyone who has spent much time with cats has heard are the growl, hiss, or spit. The shriek or scream usually happens when they are very scared or hurt. Chattering happens often when they see something like a bird or a mouse that they want to "play" with, but can't get to. A howl or yowl is often a sign that their territory is being encroached upon by another cat and they want to fight. A murmuring trill is often a greeting or a request meaning "pet me" or "feed me."

Cats purr a lot of the time, even when they are just laying around.
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When do cats purr?

The purring sound is one of the first cat vocalization a young kitten learns to make. Newborn kittens that are only a couple of days old already know how to purr. Experts think this is an early bonding mechanism between mother and kitten that tells the mother cat the kittens are ok and nearby.

As the kitten grows up, purring becomes a regular part of their communication. It seems obvious that cats purr when they are content and happy, because as soon as they start getting petted their little motor turns on. But believe it or not, purring can also be a mechanism that helps them soothe themselves when they are injured or in pain.

In fact, there is also research to suggest that purring may stimulate bone growth due to it being a healing, low vibration frequency. A study from the early 2000s in an acoustic journal suggests that the low rumble of a cat's purr occurs at frequencies that best promote bone growth and fracture healing. The purring that cats do when they are just laying around could be helping to keep their bones healthy, to make up for all that laying around that they do.

Cats that roar like lions can't purr in the way we are used to.
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How do cats purr?

Purring is so common, that you would think scientists would have figured it out by now. But surprisingly, there's not a clear understanding yet of exactly how cats purr. But the most accepted idea is that there is an area in the cat's brain called a neural oscillator that triggers the cat's voice box to vibrate. At the same time as this impulse is being sent, the cat's inhaling and exhaling sends a stream of air across the vocal cords. The vibrating creates the purring sound.

It is primarily domestic cats who purr in the way we are used to. Some wild cats purr, while others do not. The bobcat, cheetah, Eurasian lynx, puma, and wild cat also purr, while the lion, leopard, jaguar, tiger, snow leopard, and clouded leopard cats in the panther family do not exhibit true purring.

There's an anatomical difference between house cats and cats that roar that explains this. There's a bone in cats' throats called the hyoid. The hyoid bone supports the larynx, which is what we commonly call the voice box. Some big cats such as lions, tigers, leopards, and jaguars have more flexible hyoid bones that do not produce purrs but do produce loud roars.

Small cats like our house cats, bobcats, lynxes, cheetahs, and cougars, have a very rigid hyoid bone that is not flexible at all. When this bone vibrates, it produces the purring sound. Science has figured out that when a cat has a paralysis of the larynx, they cannot purr, so even though scientists don't understand completely how it is able to happen, the larynx seems to be a very important part of the purring sound.

The brain stimulation that triggers a cat's purring sound may be out of their control.
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Is purring voluntary or involuntary?

Since scientists don't have a clear understanding of how purring happens, they really don't know for sure if cat purring is a voluntary or involuntary process. The evidence seems to strongly suggest that the neural oscillator in their brain may be triggered by endorphins that are released when they experience pleasure or pain. In that sense, the brain stimulation that triggers the purring sound may be out of their control.

A feline expert, Associate Professor Vanessa Barrs at the Valentine Charlton Cat Centre with the University of Sydney, explained that purring involves both the cat's larynx muscles and diaphragm. As the cat breathes in and out, air hits the vibrating larynx muscles in the throat, which is what produces the purring sound. She says the frequency of the purr is controlled by the autonomic nervous system, which operates largely unconsciously to regulate bodily functions. However, she says that cats do have a conscious control over purring and may change the sound of the purrs they make, for instance, making a "soliciting purr" when they want to be fed.

Conclusion

We love to hear our cats purr. There is nothing better than a satisfied and happy, warm cat purring while curled up on your lap. Scientists haven't pinpointed exactly what causes the purring sound, but it seems to start with something, possibly endorphins, that triggers the neural oscillator in their brain.

That neural oscillator in turn triggers the bones that support the vocal cords and voice box to vibrate. When the cat breathes air over their vibrating vocal cords and voice box, we hear the low frequency purring sound. The bone that supports the vocal cord and voice box in wild cats that roar is slightly different anatomically than that of our domestic house cats. So most cats that roar cannot purr.

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