The muscle that causes the hair to stand on end when a person is scared or cold is known as the:

The muscle that causes the hair to stand on end when a person is scared or cold is known as the:

• A. Cuticle
• B. Papilla
• C. Medulla
• D. Arrector Pili

Answer: (D)

Hair standing up when someone is scared or cold is caused by the arrector pili muscles. These tiny smooth muscles attach to each hair follicle and, when the sympathetic nervous system is activated by fear or cold, contract to pull the hair follicle upright. This creates goosebumps and can help trap a layer of air for insulation or make us look larger to a threat. The other terms refer to parts of the hair or follicle, not muscles: the cuticle is the outer protective layer of the hair shaft, the papilla supplies blood to the follicle, and the medulla is the hair’s soft central core.

Hair standing up when someone is scared or cold is caused by the arrector pili muscles. These tiny smooth muscles attach to each hair follicle and, when the sympathetic nervous system is activated by fear or cold, contract to pull the hair follicle upright. This creates goosebumps and can help trap a layer of air for insulation or make us look larger to a threat. The other terms refer to parts of the hair or follicle, not muscles: the cuticle is the outer protective layer of the hair shaft, the papilla supplies blood to the follicle, and the medulla is the hair’s soft central core.