Final answer:
The contraction of arrector pili muscles, which causes goosebumps, is stimulated by the sympathetic nervous system's release of norepinephrine in response to feeling cold, leading to the hairs standing up and providing insulation.
Step-by-step explanation:
The arrector pili muscles are tiny smooth muscles in the skin that are responsible for producing goosebumps. These muscles contract in response to stimuli from the sympathetic nervous system. When the body feels too cool, the arrector pili muscles contract, pulling on the hair follicles and causing the hairs to stand up straight, which helps to insulate the skin by trapping more air. This contraction is stimulated by the neurotransmitter norepinephrine that is released by sympathetic postsynaptic neurons.
The arrector pili muscles are stimulated for contraction by sympathetic nervous system. When the body is too cool, these muscles contract, causing the hair follicles to rise and resulting in goosebumps on the skin. This contraction is a response to the sympathetic nervous system releasing norepinephrine, which stimulates the arrector pili muscles to contract.