Whiskers (vibrissae)
From Wigipedia, the free hair encyclopedia
A whisker, or vibrissa, is a hair, but a hair that has been promoted to instrument. Where ordinary fur is for warmth and show, vibrissae are for sensing: they are thicker, stiffer, set more deeply in the skin, and — crucially — wired into the nervous system far more richly than any normal hair.[citation needed]
How a whisker feels
The whisker shaft itself is dead keratin and cannot feel anything. The sensing happens at the root, which sits in a follicle-sinus complex — a follicle wrapped in a little blood-filled cushion and surrounded by hundreds of nerve endings. When the tip of the whisker brushes something, the shaft pivots, and the follicle reports the exact angle and force. The animal essentially reads the world through tiny levers.
The geometry of the cat
A cat carries about 24 main whiskers on its muzzle, arranged in four tidy horizontal rows on each side, plus smaller sets above the eyes, on the chin, and on the backs of the front legs. A widely cited rule of thumb is that a cat’s whisker span is roughly as wide as its body, letting it judge in the dark whether a gap is wide enough to fit through — although a well-fed cat can out-grow its own measuring sticks.
Whiskers are also expressive: pushed forward in curiosity or hunting, pinned back in fear, a running commentary on the animal’s mood.
Beyond cats
Most mammals have them. Rats sweep their whiskers back and forth in a rhythmic motion called whisking to map surfaces and textures. Seals and sea lions have spectacularly sensitive whiskers that can track the hydrodynamic trail left by a fish that swam past seconds earlier — following a meal through murky water by feeling its wake.
Humans, alas, lost theirs. We keep only the faint vestigial muscles where vibrissae once twitched — another small souvenir of a furrier past, much like goosebumps.