At the base of the follicle is a tiny involuntary muscle called the

• A. Sebaceous Gland
• B. Dermal Papilla
• C. Arrector Pili
• D. Hair Bulb

Answer: (C)

The base of the follicle contains a tiny involuntary muscle called the arrector pili. This smooth muscle is controlled automatically (not by conscious effort). When it contracts, it lifts the hair follicle upright, making the hair stand on end—a reaction we notice as goosebumps. This muscle sits attached to the hair follicle and pulls on it from the dermal layer.

The other structures have different roles: the sebaceous gland produces sebum to lubricate the hair; the dermal papilla provides blood supply and nutrients to the growing hair; the hair bulb is the growing part of the follicle at the base. None of these are muscles, so they don’t cause the hair to stand up.