Why We Get Goosebumps?

Although the connection between nerve and muscle was already known in this specific system, the link to the hair-regulating stem cells is a new discovery, and an unusual one - here, those synapse-like connections are made to stem cells instead, wrapping around them like ribbons.

The research also showed how prolonged cold puts the sympathetic nerves in a state of high alert, exceeded the normal low-level activation that they spend most of their time at. More neurotransmitters are released, triggering quicker activation of the stem cells and, ultimately, quicker hair growth.

Most importantly, the team of researchers established that the muscle was indeed an essential link between nerves and follicle stem cells – when the muscle was removed, the connection was lost. Anyway, according to the activity observed in mice, the growth of the muscles is actually triggered by the hair follicles themselves.

Biologist Yulia Shwartz says, "We discovered that the signal comes from the developing hair follicle itself. It secretes a protein that regulates the formation of the smooth muscle, which then attracts the sympathetic nerve. Then, in the adult, the interaction turns around, with the nerve and muscle together regulating the hair follicle stem cells to regenerate the new hair follicle.”

While these same interactions haven't been observed in humans yet, biological similarities between mice and other mammals in this area make it likely that the same processes are going on underneath our own skin.

The research has been published in Cell.