What is the tiny muscle attached to hair follicles that was pull the hair upright during fright or cold are called?

The tiny muscles attached to hair follicles that pull the hair upright during fright or cold are called arrector pili muscles. When these muscles contract, they cause the hair to stand on end, a response commonly known as "goosebumps." This reaction is part of the body's fight-or-flight response and also helps with thermoregulation by trapping air for insulation.