What is the role of the arrector pili muscle?

The arrector pili muscle is smooth muscle associated with hair follicles and its primary function is to cause hair to stand up, known as piloerection. This response occurs as a reaction to cold temperatures or emotional stimuli, such as fear. When the muscle contracts, it pulls on the hair follicle, causing the hair to stand upright and creating an insulating layer of air to help retain body heat. In some animals, this response can make them appear larger to predators or rivals, providing an evolutionary advantage.

The roles associated with hair growth, sweat production, and protection of hair follicles are performed by other structures and processes in the body. The arrector pili muscle does not contribute to hair growth directly, nor does it produce sweat; those functions are performed by different components within the skin. Additionally, while the muscle contributes to the overall health of hair follicles by affecting how hair stands, its primary role is related to the erection of hair. Therefore, the answer that accurately reflects the muscle’s function is the one indicating its role in making hair stand up.