How do cats purr, you may wonder as you snuggle with your cat on the couch, when you notice her expressing her content with being by your side. Purring is one of many vocalizations cats use to communicate. It is the unique anatomy of felines which makes this sound possible.
A 2002 study in Mammal Review reported that true purring is only seen in the scientific families of Viverridae and Felidae. The mechanism varies with the species. The important parts of the cat's anatomy are the vocal cords, laryngeal muscles, diaphragm and glottis. The glottis is a part of the larynx or voice box and the slit-like opening between the vocal cords. Manipulation of the vocal cords produces the different vocalizations that cats make.
Not all cats are the same. While your domestic cat can purr, big cats like the lion, leopard and clouded leopard do not purr, at least not by using the same mechanism as housecats.
How Do Cats Purr?
Feline anatomy provides the structure. Physiology causes purring to occur. The alternating action of the laryngeal muscles and the diaphragm produce air movement within the larynx. This causes a build-up of air pressure. The air is then released through the glottis.
The repetitive opening and closing of the glottis gives purring its unique sound and accounts for your ability to feel the movement within your cat if you place your hand on her side or hold your cat. The frequency of the glottis movement is about ten times that of normal respiration, according to Dennis Turner in his book The Domestic Cat: The Biology of Its Behavior.
What makes the difference between purring and roaring in domestic cats versus big cats is how respiration is used to produce the vocalization. Domestic cats purr during inhalation and exhalation. Big cats, such as the lion, produce a similar sound, but only during exhalation.
The mechanism for causing purring lies in the cat's nervous system. You may have observed that your cat purrs when she is feeling contented or relaxed. However, she may also purr if she is sick or in pain. Turner also explains that a cat may purr to signal appeasement to its human owner.
A 1972 study in Respiration Physiology explains that the act of purring may be triggered by the central nervous system, which triggers a nervous reaction and causes the glottis to oscillate. The central nervous system consists of the brain and spinal cord. These findings provide further evidence that purring may be some instinctive form of communication.
Further evidence that supports purring as a survival function comes from 2006 report in Scientific American. Purring may help improve your cat's health and increase her bone density. Even if your cat is purring in a stressful situation such as a visit to the vet, she may be relying on her own biology and physiology to heal her.
Purring with a Reason
Cats can also intensify their purring with the intent to catch your attention. According to the University of Sussex, cats may interject an embedded, high-pitched cry, not unlike the sound of a baby crying. This action occurs through manipulating the glottis and vocal cords.
Scientists refer to this type of purring as solicitation purring. If you have ever been woken up by your cat before the alarm has gone off, you may have experienced solicitation purring first hand. How could you ignore your cat purring beside your head as you try to continue to sleep? Scientists postulate that the sound of this purring solicits an instinctive reaction in humans to respond to a crying baby.
How do cats purr? The answer resides in the cat's biology and physiology with direction from the nervous system. Purring is another example of the instinctive behavior of cats to communicate and get what they want.