Why
does a cat purr?
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Since Egyptian times, cats have been revered. And surely part of the admiration we feel for felines is because of their unique ability to purr. Cats can purr as they take a breath in, or as they breathe out.
Cats can purr with their mouths tightly closed.
Kittens can purr with their mother's nipple in their mouth.
This phenomenon of suckling and purring at the same time can occur because purring is not a vocal sound.
The purr does not come from the true vocal cords. No one really knows for sure where the purr sound comes from but there are several theories on this subject.
This first theory is called the Diaphragm-Larynx Theory which maintains that the sound is based on positive pressure in the lungs causing the glottis at the back of the throat to rapidly open and close which causes the vibrations that we hear as purring.
A similar theory suggests that it's the vibrations of the false vocal cords, located right behind the true vocal cords, in the larynx that cause the sound.
The Soft-Palate Theory proposes that a cat can voluntarily "flutter" its soft palate producing the purring sound.
A third, and less accepted theory, is the Blood-Turbulence Theory. This theory suggests that the sound is produced by turbulence of blood flowing in the superior vena cava vein that is attached to the heart. It is thought that this turbulence occurs when this large vein constricts, or is compressed by the cat when it arches its back.
The feline "purr center" is located in an area of the brain near connected to the hypothalamus called the infundibulum. One function of the hypothalamus is to feel and interpret emotions. It determines if a certain sensory stimulus is pleasant, like being petted, or painful.
The interesting thing about the hypothalamus is that it releases endorphins, which are morphine-like substances, that stimulate the "purr center" causing that wonderful, vibrating purr that we are all so familiar with.
Pain stimulates the hypothalamus to release it's endorphins to help block the pain. That's why cats purr both when they are happy but also purr when they are in pain.
Kittens are born blind and deaf yet purr in response to their mother licking them. Their mother purrs so that they can find her, and purring acts to comfort both of them.
But perhaps it doesn't really matter how a cat purrs, or why it purrs. It is enough that they do purr. And that the sound of the purr reaches deep inside a person and touches something that almost seems to be a silent human purr... a silent communication that sings a duet with our feline friend.
It is . . . purr-fection