Final answer:
The B. arrector pili muscles, when contracted, cause goose bumps by pulling on hair follicles in response to stimuli like cold temperature or emotions for insulation purposes.
Step-by-step explanation:
The special smooth muscles in the dermis that, when contracted, produce goose bumps are called B. arrector pili.
These muscles are activated in response to stimuli such as cold temperatures or emotional situations.
When the sympathetic nervous system stimulates these muscles, they contract and pull on the hair follicles, causing the hair to stand up and the skin to form bumps.
This process has the effect of trapping more air under the hairs, which can help to insulate the skin and conserve body heat.