Which type of nerve is responsible for stimulating the arrector pili muscles?

• A. Afferent
• B. Efferent
• C. Interneurons
• D. Somatic

Answer: (B)

Efferent nerves, particularly the sympathetic fibers, are responsible for stimulating the arrector pili muscles, which are tiny muscles attached to hair follicles. When these muscles contract, they cause the hair to stand on end, a phenomenon often referred to as "goosebumps." This physiological response can occur in reaction to cold temperatures or emotional stimuli, and it plays a role in thermoregulation and displaying emotions.

Afferent nerves, in contrast, are involved in transmitting sensory information from the environment to the central nervous system and do not stimulate muscles. Interneurons play a role in relaying signals within the nervous system rather than directly stimulating muscle fibers. Somatic nerves generally refer to the nerves that control voluntary muscle movements and do not primarily govern the action of the arrector pili muscles, which are regulated involuntarily and are part of the autonomic nervous system.