ChoiceHub
Sign in

Arrector pili muscle

Hypodermis & appendages · detail · α1 adrenergic Piloerection Bulge niche

Small band of smooth muscle running from the follicular bulge to the papillary dermis. Sympathetic adrenergic stimulation contracts it to erect the hair, and its insertion marks the follicular stem cell niche.

Traced from the start

  1. Stratum basale (germinativum)
  2. Lamina densa (type IV collagen basement membrane)Sublamina densa anchoring fibrils (type VII collagen)
  3. Papillary dermis
  4. Reticular dermis
  5. Arrector pili muscle

Detail

Innervation
Sympathetic noradrenergic fibres acting on alpha-1 receptors; no parasympathetic supply
Attachment
Runs from the bulge region of the follicle to the papillary dermis, defining the position of the stem cell niche
Function
Piloerection; vestigial for insulation in humans but a reliable marker of sympathetic outflow

When it goes wrong

Interruption of the sympathetic supply to the face (central or preganglionic Horner syndrome)

Ipsilateral ptosis, miosis and facial anhidrosis with loss of piloerection; a painful Horner syndrome demands urgent imaging for carotid dissection

Adrenergic surge in opioid withdrawal

Piloerection with lacrimation, rhinorrhoea, yawning, mydriasis and diarrhoea — the classic withdrawal cluster

Practise this structure

No question in the bank is tagged to Arrector pili muscle yet. Questions appear here automatically once one is — the question bank is free to browse in the meantime.