"Cell": Harvard scientists did a study on goose bumps...

▎ why do we get goose bumps? If you're curious about this question, Darwin is as curious as you are.Darwin also thought about goose bumps in his works on human evolution.he noted that the erection of animal hair, feathers or spines to regulate body temperature, courtship or aggression helps to improve survival advantages.but for humans, it seems that there is no good in standing up the hair. Why has it been preserved in evolution? Recently, a new study published in the leading academic journal cell has found the answer.Professor Xu Yajie of Harvard University and his collaborators found that the cells that make goose bumps have another important function: promoting hair growth.speaking of the production process of goose bumps, people have long known that it requires the cooperation of nerves and small muscles around the hair follicles: cold or other external stimulation triggers the sympathetic nerve to send out signals, and then the hair erector muscle makes the hair in the hair follicle stand up through contraction.however, when the researchers examined the skin of mice with high-resolution electron microscopy, they found that the sympathetic nerve was not only connected to the erector pili muscle, but also to hair follicle stem cells.to be more precise, nerve fibers wrap around hair follicle stem cells like ribbons, while the erector pili muscle acts as a "scaffold"."in general, neurons regulate excitable cells through synaptic structures, such as other neurons or muscles.however, we were surprised to find that they formed synaptic structures with epithelial stem cells, which were not typical targets of neurons."said Professor Xu Yajie.} around hair follicle stem cells, nerves and muscles form a microenvironment: the sympathetic nerve secretes neurotransmitters to control the hair follicle, and the hair erector muscle supports the sympathetic nerve (photo source: reference [1]). Further analysis shows that these sympathetic nerves regulate the activation of hair follicle stem cells by secreting noradrenalin, which plays an important role in hair growth Ring.during the hair growth cycle of adult mice, hair follicle stem cells will switch between the active state and the resting state: under the active state, the hair follicle stem cells can promote cell proliferation and transform into hair; during the resting period, the hair that stops growing slowly detaches from the hair follicle, so we can see that the hair constantly experiences shedding and growth.considering that the sympathetic nerves become more active and produce more norepinephrine under the stimulation of cold, does this mean that cold can not only make skin get goose bumps, but also promote hair growth by stimulating hair follicle stem cells? To test this idea, the team designed a set of experiments in which some mice were exposed to cold temperatures of 5 degrees.in just 2 hours, the mice had a typical "chicken skin" reaction, and the hair stood up, indicating that the sympathetic nerve and the hair erector muscle around the skin and hair follicle had normal coordination.with the passage of time, it can be seen that the sympathetic nerve continues to activate and produce more norepinephrine, which leads to the faster activation of hair follicle stem cells and the early regeneration stage.sure enough, by 2 weeks, compared with mice living in a warm environment of 30 degrees, long-term cold stimulation made mice grow hair faster.} short time exposure to cold makes the hair stand upright; the mice exposed to cold for two weeks have a faster growth of new hair on their back (photo source: reference [1]) "we can see that there are two reactions to the temperature changes in the external environment: goose bumps (bristles) are a quick way to provide relief in a short period of time, but if the cold persists, there are two reactions Furthermore, this mechanism allows stem cells to know that it's time to grow a new layer of hair."the study's lead author, Dr. Yulia Schwartz, summarized.of course, as we all know, in other cases, even in the coldest weather, our hair follicle stem cells are indifferent and don't know how to grow new hair. That's another chilling story Related reading: too much pressure, gray hair? Harvard Xu Yajie's team "nature" published an article to reveal how stress promotes white hair and saves hair loss! Scientist: we're stronger. You don't have to be bald! (video attached) nature sub: is there such a good thing? [April, 2020] may be the best way to promote the growth of human hair