Which muscle causes hair to stand upright when you are cold?

Which muscle causes hair to stand upright when you are cold?

• A. Arrector Pili Muscle
• B. Capillaries
• C. Dermis
• D. Epidermis

Answer: (A)

Hair stands up when the arrector pili muscle contracts. This tiny smooth muscle is attached to each hair follicle; its tightening pulls the follicle upright so the hair shaft becomes more vertical, creating goosebumps. This action is controlled by the sympathetic nervous system in response to cold or fear. The other options don’t directly move the hair: capillaries regulate blood flow and heat, while the dermis and epidermis are skin layers that provide structure and host the follicles but don’t cause the hair to rise.

Hair stands up when the arrector pili muscle contracts. This tiny smooth muscle is attached to each hair follicle; its tightening pulls the follicle upright so the hair shaft becomes more vertical, creating goosebumps. This action is controlled by the sympathetic nervous system in response to cold or fear. The other options don’t directly move the hair: capillaries regulate blood flow and heat, while the dermis and epidermis are skin layers that provide structure and host the follicles but don’t cause the hair to rise.