Goosebumps
From Wigipedia, the free hair encyclopedia
A goosebump is what you get when a tiny muscle attached to a hair follicle contracts and yanks the hair upright, tugging the surrounding skin into a small dome. Do this across a whole arm at once and you get the familiar pebbled “goose skin.” The proper names are piloerection or horripilation, and the Latin, cutis anserina, simply means “goose skin.”[citation needed]
The machinery
Every hair on your body has a minute muscle beside it called the arrector pili. It answers to the sympathetic nervous system — the same circuitry behind the fight-or-flight surge — which is why a jolt of cold, a fright, or a wave of emotion can all set it off without your say-so. When it fires, it stands the hair on end. You cannot consciously make goosebumps appear; they are run entirely by the autopilot.
What it’s for (in animals that still have fur)
In a furry animal the maneuver is genuinely useful. Standing the fur on end in the cold traps a thicker layer of insulating air against the skin — a living down jacket. And standing it on end in a confrontation makes the animal look bigger and more dangerous: a startled cat’s bottlebrush tail and a bristling dog’s hackles are piloerection put to work.
Why humans bother at all
We kept the wiring but lost most of the fur, so on a human the whole apparatus fluffs up almost nothing. Goosebumps are a textbook vestigial reflex — a leftover from hairier ancestors, much like the muscles that let some people wiggle their ears, or the faint relic of whiskers.
Curiously, the same little muscles may not be entirely useless: research has found that the arrector pili and its nerve help maintain the stem cells that regenerate the hair follicle. So the muscle that gives you chills during a good song may also be quietly helping keep your hair growing.