Anatomy Practice Exam 2025 - Free Anatomy Practice Questions and Study Guide

The arrector pili muscle is a small muscle attached to hair follicles. When this muscle contracts, it pulls the hair follicle upright, which results in the hair standing on end. This phenomenon is commonly known as "goose bumps." The contraction of the arrector pili muscles is often a physiological response to cold temperatures or emotional stimuli such as fear, effectively creating an insulating layer of air or making an individual appear larger in response to threats. This mechanism is part of the body's autonomic nervous system response.

The other options do not accurately describe the function of the arrector pili muscle. Hair growth is regulated by different biological processes that occur in the hair follicle itself and are not directly influenced by the contraction of arrector pili muscles. While sweat production is a function of sweat glands rather than the arrector pili muscles, blood flow to the skin is regulated by the dilation and constriction of blood vessels, not by the contraction of these specific muscles.