What happens when arrector pilli muscles contract?

When arrector pilli muscles contract, they cause the hair shafts to stand up straight. This can happen for a variety of reasons, such as:

* In response to cold temperatures: When the body is cold, the arrector pilli muscles contract to help trap heat close to the skin. This is why you get goosebumps when you're cold.

* Fear or anger: When the body is experiencing fear or anger, the arrector pilli muscles may contract as part of the body's fight-or-flight response. This can make the hair stand up on end, making the person look more intimidating.

* Sexual arousal: The arrector pilli muscles may also contract during sexual arousal, as part of the body's response to touch. This can cause the nipples to become erect and the pubic hair to stand up.

The contraction of arrector pilli muscles is controlled by the sympathetic nervous system. This system is responsible for regulating many of the body's automatic functions, such as heart rate, breathing, and digestion.