We notice occasionally that we have raised pimple-like areas on our skin each with a hair in its centre, when we enter into the chillness of outdoors or when we are excited much on seeing 'hair-raising' scenes. These raised skin areas are all well known as goose bumps (or goose flesh). How they are made?
A tiny muscle called Erector pili (or Arrector pili) does that job of making the hair stand erect! Every hair of our body has one of this muscle attached to its shaft under the skin. This muscle is of Smooth muscle type and is innervated by sympathetic nerve (a subsystem of Autonomic nervous system). We cannot use this muscle voluntarily. It is stimulated by the impulses generated by excitement that travel down to it through the sympathetic nerves. On such stimulation all of these muscles contract themselves involuntarily, thereby raising the hairs upright. In animals (mammals), that have lengthy hairs, these muscles contract to provide air spaces between the hairs giving insulation to the skin from the outer chilling climate - a natural protection that Nature has offered to these animals for retaining heat.
These are the wonder muscles that raise each of our hair in wondering about such wonders!
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