The muscle responsible for generating goose bumps is called the arrector pili muscle. These small, smooth muscles are attached to hair follicles in the skin. When the body experiences certain stimuli, such as cold temperatures or emotional responses like fear, the nervous system signals the arrector pili muscles to contract.
This contraction pulls the hair follicles upright, causing the hair to stand on end and creating the appearance of goose bumps. This response is often a remnant of our evolutionary past, where raising body hairs made our ancestors appear larger to potential predators or helped retain body heat.