What effect do arrector pili muscles have on the hair follicle?

• A. They assist with blood flow.
• B. They contract to cause goosebumps.
• C. They produce keratin.
• D. They insulate the hair.

Answer: (B)

The arrector pili muscles are small, smooth muscles that are attached to hair follicles. When these muscles contract, they pull on the hair follicle, causing the hair to stand upright. This phenomenon is commonly known as "goosebumps." The contraction of the arrector pili muscles occurs as a reflex response to cold temperatures or emotional states such as fear or excitement. This response not only makes the hair stand on end, creating goosebumps, but can also slightly increase insulation by trapping air beneath the hair, which is an evolutionary remnant from when our ancestors had thicker body hair.

The other options do not accurately describe the primary function of arrector pili muscles. They do not assist directly with blood flow, nor do they play a role in the production of keratin, which is mainly done by keratinocytes in the epidermis. Insulation provided by hair is a result of its ability to trap air, but the arrector pili muscles themselves do not provide insulation; rather, they alter the position of the hair. Therefore, the correct assessment of the role of arrector pili muscles is that they contract to cause goosebumps.