What is the primary function of the arrector pili muscle?

The primary function of the arrector pili muscle is to contract in response to cold or emotional stimuli. This involuntary muscle is attached to hair follicles and is responsible for causing the hair to stand upright, a phenomenon often referred to as "goosebumps." When the body is cold, or when an individual experiences strong emotions such as fear or excitement, the arrector pili muscles contract, leading to this raised hair reaction.

This contraction serves several purposes. In terms of thermoregulation, the raised hairs create an insulating layer of air, which can help retain body heat. Additionally, in the context of emotions, the hairs standing on end can be a response that makes an animal appear larger to potential threats, acting as a defense mechanism.

The other options do not accurately describe the primary role of the arrector pili muscle. While the production of sweat is crucial for thermoregulation, this function is carried out by sweat glands rather than the arrector pili. Supporting the structure of hair follicles is a function of the hair follicle itself and surrounding tissues, not specifically of the arrector pili muscle. Finally, absorption of ultraviolet rays is a function related to the skin's pigment cells, not the muscular structures associated with hair