Where Do Purrs Come From?

Where Do Purrs Come From?

A cat’s purr is indeed a wondrous thing. It’s a sign of a content cat, a cuddly cat, a cunning, manipulative and ‘far superior than thou’ cat. A cat’s purr has such a pacifying effect on the cat’s owners. But why does the cat seem to vibrate and shake so strongly when the purring really gets going? Have you ever thought about where in that furry, soft body the purr actually comes from?

What Cats Purr? 

Charles Darwin recorded the occurrence of purring not only in domestic cats, but also in cheetahs (they purr quite loudly), pumas and ocelots. Tigers also appear to emit a purry sort of snuffle, but lions, jaguars and leopards do not purr.

Cats obviously seem to purr when they are pleased or content and when they are hungry and want food. They know it affects humans and is likely to get the food bowl attended to. Of course, this purr stops immediately the food bowl is presented and is then replaced by that independent, aloof and even downright unfriendly feline mood that comes with a full stomach.

A cat’s purr seems to be Creation’s compensation for the fact that a cat cannot use a can opener!

A female cat will purr during mating, and both she and are her kittens will purr while the kittens are suckling. However, cats will also purr when they are sick and, curiously, will often purr when terminally ill and shortly before death, akin, perhaps to the state of euphoria often seen just before death in terminally ill human cancer patients.

Two researchers from Canada, Stogdale and Delack, have written a paper about cats and purring.

Old Theories of Purring

They state that two early theories regarding the mechanism of purring are scientifically groundless, but nevertheless interesting. One claimed that purring was caused by the echoing of the vibration of blood in the vena cavae – a large blood vessel in the chest of the cat. Another theory is that the effects of blood flow caused by the bending of the aorta when a cat arches its back causes purring. Well, the gurgling blood theories are not true.

Purring occurs in during both inspiration and expiration, unlike human speech which occurs only during expiration.

When your cat purrs, you can feel the vibration in the cat’s throat and also in the cat’s chest.

So where does it come from?

With humans, speech originates from the larynx or voice box in the throat and it is natural to assume that a cat’s purr comes from the same organ and you can only feel it in a cat’s chest because it vibrates down the windpipe to the chest.

Humans cannot talk if the larynx is bypassed, with, for example, a tracheostomy tube (those tubes installed in a patient’s neck when they cannot breath through their mouth). However cats can purr if their larynx is bypassed in the same manner. Thus the origin of the purr is not just the larynx, even though the purr can be felt in the cat’s throat.

The researchers found that purring is actually caused by rapid vibrations in the muscles of the larynx and the diaphragm working in harmony.

The vibrations in each of these muscles take their turn, one waiting for its partner to finish before it starts. This alternating vibration recurs about 30 times every second. These vibrations cause air turbulence which is the sound that is heard but in addition, the actual muscle vibrations in the larynx and the diaphragm can also be felt in the cat’s neck and its chest respectively.

That’s why when a cat is turning on its charm, its whole body seems to rumble with that percolating, gurgling purr that many of us know so well. It’s not the sound that causes the body rumbling, it’s the muscle movements.

But wait there’s more! Our voice is caused by vibrations too – vibrations of our vocal cords – but we’re silly because our vocal cords will only vibrate properly when the air goes out during expiration, not when it comes in. Try talking while breathing in. You can do it but it doesn’t sound very pleasant.

By comparison, the purr of a cat is virtually identical while they are breathing either in or out.

Indeed while purring, they are hyperventilating and are doubling their air intake as well as increasing their heart rate. Which just goes to show that while we may enjoy a cat’s purr, it’s not a one way street as purring is also good for your cat – especially if it results in food. So, who’s the boss?.

Review questions

  1. Do leopards purr?
  2. Do cheetah’s purr?
  3. Is purring causes by vibration of blood in the vena cavae?
  4. Or is is caused by rapid vibrations in the muscles of the larynx and the diaphragm working in harmony?
  5. Do cats purr when breathing in, breathing out or both?