A hair or pilus is a slender filament of keratinized cells. It has three divisions: the bulb-where the hair originates in the dermis or hypodermis, the root-the remainder of the hair within the skin, and the shaft-the portion of the hair extending above the skin (superficial). The vascular papilla found in the base of the bulb fuels the mitosis of the keratinized cells. The hair also has neuronal receptors sensing movement of the hair. The piloerector muscle cause the hair to stand up.