What happens when the arrector pili muscle contracts?

What happens when the arrector pili muscle contracts?

• A. Hair grows longer
• B. Hair stands upright
• C. Hair color changes
• D. Hair becomes oily

Answer: (B)

When the arrector pili muscle contracts, hair stands upright. These tiny smooth muscles attach at the base of each hair follicle and, when they tighten, pull the follicle into a more vertical position. That causes the hair shaft to lift, producing the familiar “goosebumps” effect. This reaction is part of the autonomic nervous system and is often triggered by cold or emotional stimuli. In humans it’s largely vestigial, but the mechanism remains the same. Hair growth, color changes, and oil production involve different processes: growth comes from the follicle’s growth cycle, color from pigment cells, and oiliness from sebaceous glands—none of which are caused by arrector pili contraction.

When the arrector pili muscle contracts, hair stands upright. These tiny smooth muscles attach at the base of each hair follicle and, when they tighten, pull the follicle into a more vertical position. That causes the hair shaft to lift, producing the familiar “goosebumps” effect. This reaction is part of the autonomic nervous system and is often triggered by cold or emotional stimuli. In humans it’s largely vestigial, but the mechanism remains the same. Hair growth, color changes, and oil production involve different processes: growth comes from the follicle’s growth cycle, color from pigment cells, and oiliness from sebaceous glands—none of which are caused by arrector pili contraction.