Vitals & Bits #10: Piloerector Muscles

You know that feeling you get on a beautiful Albuquerque summer evening, when dark purple clouds sit heavily on the northern horizon while the setting sun jettisons the vast western sky with its searing pink and orange afterthoughts? Ok, so I’m no lyricist. But you know what I mean. Our anxiety-riddled, consumption-driven, Facebook-centric modern lives are occasionally punctuated by moments so stunning that your hair literally stands on end.

The “hair standing on end” sensation of life’s finest “Aha!” moments is brought to you courtesy of your arrectores pilorum, or the small muscles attached to your hair follicles. When these muscles contract, they tug on your hair follicles, which causes your hair to stand on end.

The arrectores pilorum, or piloerector (pilo meaning “hair” and erector meaning, um, erection) muscles are not under voluntary control. These muscles are micromanaged by your autonomic nervous system, or the branch of your nervous system that does all kinds of cool crazy shit on its own without you thinking about it (like controlling your heart rate or digestive muscles.)

Certain physical sensations, like cold, will stimulate your autonomic nervous system to activate your piloerector muscles. This is because other furry mammals, like cats and dogs, control their body temperature by puffing up when they’re cold. This allows their fur to trap more body heat. Unfortunately (or rather, fortunately), humans don’t have enough hair to make piloerection an effective method of insulation. Because of this, the ability to piloerect is probably vestigial.

Emotionally-based sensations, such as fear, excitement, or awe can also stimulate the autonomic nervous system to activate the piloerector muscles. While we humans experience this “hair standing on end” sensation as a rather cosmic sixth sense, it is probably also a vestigial function of our hair follicles. You’ve probably seen a cat puff up when he’s spooked. Aside from being hilarious, piloerection allows cats to appear bigger and tougher when they encounter potentially harmful entities, like a neighbor’s dog or a rogue Tickle Me Elmo. Again, humans don’t have enough hair to make piloerection a very useful method of intimidation (though I am having fun picturing rival sports teams puffing up their hairdos as a form of pre-game posturing.)

Still, thinking of the itty-bitty, eager little muscles attached to my hair follicles fills me with appreciation for the fascinating minutia of the human body. While piloerection may not serve a definitive purpose in the human body, it at least allows me to feel all goosebumpy and electric when I contemplate the mind-warping mysteries of life.