The arrector pili consists of smooth muscle tissue.
It consists of narrow diamond-shaped cells with a single, centrally located nucleus. Each cell must be separately stimulated by nerves of the autonomic in order to contract.
The arrector pili (“raiser of the hair”) is a band of muscle tissue that connects a follicular unit to the dermis.
Contraction of the arrector pili is involuntary.
Stresses such as cold and fear may stimulate the autonomic nervous system and cause contraction — making the hair stand on end.
In humans, the result is called goose bumps.