Conversation so far:
what is one major function of arrector pili muscle contraction
In order to generate heat when the body is cold, the arrector pili muscles contract all at once, causing the hair to stand up straight on the skin.
what is the arrector pili muscle composed of
Each arrector pili is composed of a bundle of smooth muscle fibres which attach to several follicles

Question: what is the muscle innervated by
Self-contained rewrite: what is the arrector pili muscle innervated by