Sample Response: The brain, through the nervous system, sends signals to the muscular system, causing the muscles to move rapidly. This rapid motion produces heat in the body and is observed as shivering. The brain also sends signals to the muscles right beneath the skin. These muscles shorten and tighten, causing the hairs on the skin to stand up. When the hairs stand up, heat is kept in the air trapped within the hairs, which keeps the body warm.
