Final answer:
The contraction of the arrector pili muscle causes hair follicles to move and hair shafts to stand up, creating goosebumps and helping to conserve body heat by trapping more air for insulation.
Step-by-step explanation:
When the arrector pili muscle contracts, it results in the movement of hair follicles and the lifting of hair shafts, a process commonly known as goosebumps. This reaction is part of the body's thermoregulatory mechanisms, occurring when the body needs to conserve heat. The raised hairs trap more air, which provides additional insulation and reduces the loss of body heat.
In broader terms, smooth muscle tissues, like the arrector pili, facilitate various involuntary movements and functions in the body. For instance, smooth muscles in blood vessels assist in regulating body temperature via vasoconstriction and vasodilation, while those in the digestive system propel food through peristalsis. Muscle contraction across different muscle types occurs when muscle fibers shorten, responding to signals from neurotransmitters such as acetylcholine (ACh).