What is the function of the arrector pili muscle?

The function of the arrector pili muscle is primarily to cause goosebumps. These small, thin muscles are located at the base of hair follicles. When they contract, which can occur in response to cold temperatures or emotional stimuli (like fear or excitement), they pull the hair upright and create the phenomenon known as goosebumps. This reaction is part of the body's natural responses, intended to insulate the body by trapping a layer of air when cold, or to make a person appear larger when threatened.

The other options, while related to skin and hair, do not accurately describe the primary role of the arrector pili muscle. Blood flow, skin temperature regulation, and hair growth involve different physiological mechanisms and structures in the body, rather than the direct action of the arrector pili muscle itself.