Final answer:
The arrector pili muscles are made up of smooth muscle tissue that is controlled involuntarily by the autonomic nervous system, contributing to thermoregulation and emotional responses like goosebumps.
Step-by-step explanation:
Arrector Pili Muscles
The arrector pili muscles are composed of smooth muscle tissue. Unlike skeletal muscles, which are under voluntary control, the arrector pili are controlled by the autonomic nervous system and respond involuntarily to stimuli such as cold temperatures or emotional states, causing hair to stand on end -- a phenomenon commonly referred to as goosebumps. These muscle fibers are connected to the hair follicles found in the skin and are responsible for pulling the hair upright during contraction.
When the body is too cool, various physiological responses occur to conserve body heat. The blood vessels in the skin constrict, sweat glands reduce their activity, and the arrector pili muscles contract, causing the hair to stand up and trapping more air, which acts as an insulating layer for the skin. This contraction of the arrector pili is what results in goosebumps.
In summary, the muscle tissue that makes up the arrector pili muscles is smooth muscle. These muscles play a crucial role in the body's thermoregulatory processes and are also associated with the emotional response that triggers goosebumps.