Arrector pili

Arrector pili is a small, involuntary muscle composed of smooth muscle cell.  It attaches to the hair bulb of the hair follicle and act to pull the hair up during cold or emotional distress, forming the “goose bump” on skin surface.

Scalp.  Notice the hair follicle in the middle and the string of muscle attaches to its base from the right.  This muscle is known as arrector pili.  Structure highlighted here.  (TM: 100x, picture taken with a Nikon Plan Apo 10/0.4 on Sony A7ii)
From the same slide as above showing the attachment of arrector pili to the base of the hair follicle (hair bulb).  (TM: 400x, picture taken with a Zeiss Planapo 40/1.0 Oil on Sony A7ii)

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