What is the role of the arrector pili muscles?

The arrector pili muscles are small, thin muscles attached to hair follicles in the skin. Their primary function is to cause the hair to stand erect when they contract, a response often referred to as "goosebumps." This reaction can occur in response to cold or emotional stimuli, such as fear or excitement. When these muscles contract, they pull the hair follicle upright, which may create an insulating layer of air and can make the individual appear larger to potential threats.

This physiological response is an evolutionary remnant from when our ancestors had much thicker body hair, which helped them retain warmth or appear more formidable to predators. Understanding the role of the arrector pili muscles provides insight into how our body responds to environmental changes and stressors.