The arrector pili muscle is responsible for which action?

• A. The hair to stand on end
• B. The skin to tighten
• C. The skin to absorb moisture
• D. The production of sebum

Answer: (A)

The arrector pili muscle is a small, involuntary muscle located at the base of hair follicles. When stimulated, this muscle contracts, causing the hair to stand on end, a phenomenon commonly referred to as "goosebumps." This reaction can occur in response to cold temperatures or emotional stimuli, such as fear or excitement.

While the other options related to skin tightening, moisture absorption, and the production of sebum may involve other physiological processes or structures in the skin, they do not pertain to the specific action of the arrector pili muscle. For instance, skin tightening typically involves the contraction of different types of muscles or the action of the dermis, while moisture absorption is related to the skin's barrier functions and hydration processes. Sebum production is primarily governed by sebaceous glands associated with hair follicles, but not directly by the contraction of the arrector pili muscle. Thus, the correct answer highlights the specific role that the arrector pili muscle plays in relation to hair follicles.