31 July 2020

Understanding Goosebumps

Welcome back. You’ve been waiting on pins and needles. Finally, it can be told! We now understand  goosebumps (or goose bumps). 

To avoid confusion with R.L.Stine’s exciting series of Goosebumps books, please note that I’m referring to the little bumps on a person's skin which may develop involuntarily when the person is cold, tickled or experiencing strong emotions. The affected skin resembles that of a plucked goose and, in years past, was described as goose-flesh (1803), goose-skin (1761), goose’s skin (1744) and hen-flesh (early 15th century). Many other languages use “goose” to describe the phenomenon; some use a different bird. But I digress.

Close-up photo of goosebumps and hair standing on end (from scitechdaily.com/charles-darwin-investigated-goosebumps-now-harvard-scientists-discover-the-real-reason-behind-them).
Lest you think the topic is trivial, the discovery came in a study conducted by an international team affiliated with Harvard, National Taiwan and Rockefeller universities, ETH Zurich and Howard Hughes Medical Institute.

Be warned, goosebumps serve no practical purpose. Unlike fur-covered animals, where a similar phenomenon may make them look larger and more threatening, in addition to keeping them warmer by increasing the air between hairs, we’re rather hairless (some more than others). The study was performed with mice, yet the findings explain why goosebumps survived human evolution.

Here’s what we knew and what they found.

What We Knew
Our skin is made of three types of tissue--epithelium, mesenchyme and nerve--and has multiple stem cells surrounded by diverse cell types.

The sympathetic nerve, part of the nervous system that controls body homeostasis and response to external stimuli, connects with a tiny smooth muscle in the mesenchyme. This muscle in turn connects to hair follicle stem cells, a type of epithelial stem cell critical for regenerating the hair follicle as well as repairing wounds.

The association between the sympathetic nerve and the muscle is well known, since it is the cellular basis behind goosebumps. Cold triggers the nerve to send a signal, and the muscle reacts by contracting. This causes the hair to stand on end and the skin around the hair to pull inwards, creating the bumpy skin texture.

What’s New
The researchers examined the skin with extremely high-resolution electron microscopy and found the sympathetic nerve fibers actually wrapped around the hair follicle stem cells like a ribbon.

The sympathetic nervous system is normally active at a low level to maintain body homeostasis. They found this low level of nerve activity maintained the hair follicle stem cells poised for regeneration. When the tissues were exposed to prolonged cold, however, the nerve was activated at a much higher level. A flood of neurotransmitters was released, causing the stem cells to activate quickly, regenerate the hair follicle and grow new hair.

Responding to cold, the muscle (pink) in the hair follicle contracts, resulting in goosebumps. In addition, the sympathetic nerve (green) releases neurotransmitters that target hair follicle stem cells (blue), causing them to activate and grow new hair (from news.harvard.edu/gazette/story/2020/07/the-hair-raising-reason-for-goosebumps-is-revealed/).
Delving deeper, the researchers determined how the nerve reaches the stem cells in the first place. The developing hair follicle secretes a protein that regulates the formation of the smooth muscle, which then attracts the sympathetic nerve. That interaction reverses in the adult; the nerve and muscle regulate the hair follicle stem cells to regenerate the new hair follicle. It's a loop with the developing hair follicle establishing its own niche.

Wrap Up
In summary, goosebumps appear to be part of a two-phased response to cold. In the short term, the sympathetic nerve reacts by contracting the muscle below the skin to form goosebumps. If the cold persists, the second phase kicks in. The sympathetic nerve drives hair follicle stem cell activation, new hair growth and repairs for the old ones.

The researchers suggest future study explore how the external environment influences skin stem cells under both homeostasis and in repair situations such as wound healing. Because the skin is the interface between our body and the outside world, the skin’s stem cells can potentially respond to a variety of internal or external stimuli. This affords the opportunity to study what mechanisms the stem cells use to integrate tissue production with changing demands.

See? None of this is trivial. Thanks for stopping by.


Background on Goosebumps:
Goosebumps study in Cell journal: www.sciencedirect.com/science/article/abs/pii/S0092867420308084
Article and short video on study:

1 comment:

  1. This is promising. If I wear an ice pack on my head, perhaps I could restart hair growth. Might be more unpleasant than it's worth.