Final answer:
The arrector pili muscle is responsible for goose bumps when a person is cold or nervous.
Step-by-step explanation:
The arrector pili muscle is responsible for goose bumps, which form when a person is cold or nervous. When the body is too cool, these muscles contract and move the hair follicles, causing the hairs to stand up straight, resulting in goosebumps.
Goosebumps, also known as piloerection or piloerector reflex, are the small, raised bumps on the skin that occur involuntarily in response to various stimuli. This phenomenon is caused by the contraction of tiny muscles called arrector pili muscles, which are associated with hair follicles. When these muscles contract, they cause the hair follicles to stand upright, creating the appearance of goosebumps on the skin.