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Monday 20 November 2017

A cat's whiskers extend the feline sense of touch

By Pete Wedderburn - Animal Doctor

All animals apart from humans have vibrissae, or whiskers.
All animals apart from humans have vibrissae, or whiskers.

A reader wrote to me recently with a question: she's used to finding cat fur around her home from time to time (it's part of the normal moulting process in a cat) but she had recently found a couple of entire whiskers. She wanted to know if it was normal for her cat to lose whiskers, or was there something wrong with her pet?

Whiskers are a fascinating part of cats - and other animals. They are a specialised type of hair, known as "vibrissae", and they have a particular function, acting as a sensory extension of the surface of the skin. They are longer, stiffer and thicker than normal hairs, they have a rich nerve supply around their roots, that connects them directly to the part of the brain that deals with the sense of touch, known as the somatosensory cortex. Although cats' whiskers are the vibrissae that people are most familiar with, they are present in every mammal apart from humans, from shrews right up to primates, including marine mammals like dolphins. In fact, even humans have a form of vibrissae: the tiny, bristly hairs inside your nose are also known by this name.

Vibrissae allow animals to extend their sense of touch beyond the limits of their skin. When a vibrissa comes into contact with something in the environment, the animal's brain is sent messages about the shape, size and position of the object that has been touched. It's easy to forget about the value of our own sense of touch because our vision tends to dominate our consciousness. But if you close your eyes and feel a familiar object like a coffee mug, you'll be reminded of the information that you get from touch. If you can then imagine getting similar information about things around you from whiskers protruding from both sides of your face, you'll begin to understand the value of vibrissae to animals.

Vibrissae are normally found in specific places on animals' bodies, and if you check your own dog or cat, you'll be able to identify these. There are a few small vibrissae on the underside of a cat's wrist, but most of them are on the head. There are small numbers above the eyes ("supraorbital"), on the cheeks ("genal"), and on the underside of the jaw ("mandibular"). But the biggest, most dense collection of vibrissae is the group that grow from the upper lip area, of which cats' whiskers are the most well known. These are known as "mystacial", a word with the same derivation as "moustache", because the whiskers sprout from the same part of the body.

If you look closely, you'll find that there are two distinct types of hair on the upper lip of a cat or dog. First, there are large, mobile whiskers that point out to the side. Then there are smaller, shorter whiskers, just below the nostrils, that point downwards.

The sideways-facing whiskers are the ones that everyone thinks of first, with the traditional belief that cats use them to judge the width of openings before dashing through. There was even a theory that the length of these whiskers grew or shortened to match the width of a cat's body: this was easily dismissed by carrying out studies that measured cats' whiskers as they grew fatter or thinner (they remained unchanged).

The smaller, downwards-pointing whiskers are used for fine-tuning when examining objects directly in front of cats, such as after catching small prey or investigating the opening of a burrow.

All vibrissae have rich innervation at their base, making them very sensitive to movement. Like normal hairs or nails, they are made of keratin, so they are not living, sensitive structures. It doesn't hurt to have whiskers trimmed, although the rich sensory nerve supply means that if they are tugged or moved suddenly (e.g. as might happen if they are being cut), it's very likely to cause distress.

Whiskers are mobile, as you'll see if you watch your cat investigating something unfamiliar. Small muscles at their roots allow them to move up and down, backwards and forwards. This helps animals get a better understanding of their surroundings, and it also allows them to use their whiskers as a type of social signally. Just as humans can send out messages to others by raising eyebrows, so animals can communicate by twitching their whiskers in different ways.

Scientists studying whiskers have proven that they're an effective way of helping animals navigate their environment, and as is often the way, the idea has been borrowed by technology. A robot, ("Shrewbot"), has been given mechanical whiskers to allow it to find its way around.

Back to the question that I started with: is it normal for whiskers to fall out? As specialised hairs, whiskers have their own growth cycle, with the same phases of sprouting, maturity, and shedding as normal hairs. The cycle is longer, because they are bigger hairs, and it doesn't have a seasonal pattern. It takes place in a mosaic, random pattern, so that a cat never loses all its whiskers at one time.

So yes, it is normal for whiskers to fall out individually, and if you're a house proud person, you may find occasional examples on your furniture and carpets.

As you pick them up, pause and reflect on the miracle of the way that animals' bodies are made: aren't they amazing?

Wexford People

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