Cats ability to purr is one of the most distinctive features. It is the most common sound but also one of the most puzzling. The question why cat purr has been contemplated for centuries and there are several theories derived.
The triggering mechanism of the purring is speculative. Some say the lulling noise is caused by the cats blood vessels, while others point to bone vibration. Researchers believe purring is caused when a cat’s brain sends signals to muscles in the larynx that cause the glottis to vibrate. Combined with the steady inhalation and exhalation of air as the cat breathes, passing air causes vibrations that result in the purring sound. The purring sounds is continuous because it happens when cats are inhaling and exhaling.
Domestic cats purr at a frequency of 20 to 30 vibrations per second. Purring of some cats can be as loud as hearing it across the room. While others are so quiet that the cat purring can only be felt by the vibration. Cats often purr as a sign of contentment. For example, when being petted or as result of becoming relaxed. Many people do not realize that cats also might purr when nervous, when distressed or in pain. This is common for mother cat to purr during labour. Some research suggest purring can trigger a cat’s brain to release a hormone which helps it in relaxing and acts as a pain reliever.
There is speculation that the vibration frequency of a cat’s purring stimulates muscles and bones and may promote healing in both cats and humans. Results of just stroking a cat has been shown to lower blood pressure and stress. The sound of the cat’s purring near us usually makes us feel more relaxed since we associate purring with contentment. We begin stroking the purring cat and that exchange is very comforting.