What about a cat's vocal cords allows it to purr?

Question

I know they purr when they love you.

Answer 1

Despite being a universally recognized phenomenon, the exact mechanism by which the cat purrs has been frustratingly elusive for scientists. This is partly because the cat has no obvious anatomical feature unique to it that would be responsible and may also be partly because a cat placed in a laboratory for examination is unlikely to make the noise.

One theory is that cats produce the purring noise by vibrating their larynx, or voice box, in a particular manner. A timing mechanism in the brain sends neural messages to a muscle in the larynx, rhythmically opening and closing the air passage approximately 25 times per second. Combined with the steady inhalation and exhalation of air as the cat breathes, a purring noise is produced with strong harmonics.
It was once believed that only the cats of the Felis genus could purr; some older texts may still say this. In fact, all cats are able to purr. However, the entire Panthera genus is able to purr only while exhaling. Cats that are not members of the Panthera, even larger ones such as the cheetah, purr.

Answer 2

The Physiology of Purring

There seems to be two schools of thought here.

The most popular one is quoted here:
One study determined that purring involves activation of nerves within the voice box. These nerve signals cause vibration of the vocal cords while the diaphragm serves as a piston pump, pushing air in and out of the vibrating cords, thus creating a musical hum. Veterinarian Neils C. Pederson, author of Feline Husbandry, believes that purring is initiated from within the central nervous system and is a voluntary act. In other words, cats purr only when they want to.

The other theory is that the sound comes more from vibrating blood vessels than in the voicebox itself.

Answer 3

They force air past their vocal chords which makes them vibrate. That is why they can purr when breathing in as well as out.

Answer 4

it's believed that it isn't the vocal cords that makes the purring sound, but the vibration of a blood vessel in the throat