Why does hair stand on its own when people feel cold or scared?

The steady state of our human body needs three systems to maintain, one is the nervous system, the other is the experience system and the other is the immune system. These three systems also protect our bodies. When our bodies feel cold, our cold receptors are actually in the skin. If the skin feels cold, it will send this cold signal to the cerebral cortex, which is the highest nerve center of our body, and then the cerebral cortex will control our next series of reactions.

The cerebral cortex transmits this cold strategy to the hypothalamus, which is also a nerve center. It releases some hormones and transmits them to the pituitary gland. After the pituitary gland receives the signal of this hormone, it will also release the corresponding hormone to maintain the steady state of the body. This is the regulation of body fluids, which will release corresponding hormones to increase heat production or reduce heat dissipation. At the same time, the nervous system in our body will also help us increase heat production or reduce heat dissipation. We all know that people can't help shivering when it's cold. This kind of beating, which we call skeletal muscle trembling in biology, can help us generate heat and drive away the cold.

As you can see, when we are cold or afraid, our pores will shrink and swell, and our hair will stand on end. This phenomenon is biologically called hair muscle contraction. The purpose of skeletal muscle trembling is to help us generate heat, and the purpose of hair muscle contraction is to help us reduce the loss of heat in the body and make us no longer feel cold. This phenomenon will disappear naturally when we return to the normal temperature of the body, that is, 37℃, through body fluid regulation and this nerve regulation.