Is arrector pili voluntary or involuntary?

The arrector pili muscles are involuntary. This means that they are not under conscious control and do not require conscious thought to function. The arrector pili muscles are activated by the sympathetic nervous system, which is part of the autonomic nervous system. The autonomic nervous system controls involuntary bodily functions, such as heart rate, digestion, and breathing.

When the arrector pili muscles are activated, they contract, which causes the hair shafts to stand up. This is known as piloerection. Piloerection occurs when a person is cold, scared, or angry. It is also a common response to sexual arousal.

Piloerection is a natural reflex that helps to protect the body. When the hair shafts are erect, they trap a layer of air close to the skin. This layer of air acts as an insulator, which helps to keep the body warm. Piloerection can also help to make a person look larger and more intimidating, which can be helpful in deterring predators or aggressors.