Why does it get goose bumps when it's cold?

When people feel cold or scared, the pores of the skin will shrink rapidly, which is also commonly known as goose bumps. Goose bumps are a unique physiological phenomenon for warm-blooded animals to maintain a certain body temperature. When the brain senses cold, tension or terror, sympathetic nerves work when they are nervous and excited, which affects the contraction of hair tendons and leads to goose bumps. The raising rib is located near the root of the body hair. When it contracts, the horizontal body hair will stand up at ordinary times. The hair roots protrude around to form a concave-convex shape like a bird's skin. After goose bumps, in addition to the heat generated by muscle contraction, closing pores also has the effect of keeping out the cold. When an animal with long body hair stands up, the gap between the body hairs is conducive to heat preservation. This is an experience that everyone has had. When the weather is cold and their clothes are not warm enough, they will not only feel very cold, but also tremble all over. Moreover, a layer of goose bumps will appear on their skin.