What muscle is responsible for the movement of hair follicles, causing goosebumps?

The muscle responsible for the movement of hair follicles, leading to the phenomenon known as goosebumps, is the erector pili. This muscle is a small, involuntary smooth muscle located at the base of hair follicles. When stimulated, often due to cold or emotional responses, the erector pili muscles contract. This contraction pulls the hair follicles upright, which compresses the sebaceous glands accompanying the hair follicles and also creates the appearance of goosebumps on the skin surface. This is a reflex mechanism that is part of the body's response system, aimed at providing insulation or making the body appear larger in the face of threats.

In contrast, the latissimus dorsi is primarily a muscle of the back involved in arm movements, the trapezius plays a key role in moving the shoulders and neck, and the deltoid is responsible for shoulder abduction, flexion, and extension. None of these muscles directly influence hair follicles or the sensation of goosebumps.