Arrector Pili Muscles

Definition

Arrector pili muscles are small, slender muscles attached to the hair follicles in the skin. Their primary function is to contract, causing the hair to stand upright and the skin to develop a bumpy appearance, known as goosebumps or piloerection.

5 Must Know Facts For Your Next Test

1. Arrector pili muscles are composed of smooth muscle fibers and are innervated by the sympathetic nervous system.
2. The contraction of arrector pili muscles is a reflex response to stimuli such as cold, fear, or excitement, which triggers the release of norepinephrine.
3. Piloerection, or the standing up of hairs, is believed to have evolved as a mechanism to trap air and conserve body heat in mammals.
4. Arrector pili muscles are found throughout the body, but are most prominent on the scalp, arms, and legs.
5. The contraction of arrector pili muscles can also play a role in the expression of emotions, such as fear or anger, by altering the appearance of the skin.

Review Questions

• Explain the primary function of the arrector pili muscles and how they contribute to the integumentary system's functions.
  • The primary function of the arrector pili muscles is to contract, causing the hairs on the skin to stand upright, a process known as piloerection. This response helps the integumentary system to conserve body heat by trapping air close to the skin, and can also play a role in the expression of emotions through the altered appearance of the skin. The arrector pili muscles are an important component of the integumentary system's ability to respond to environmental and physiological stimuli.
• Describe the anatomical relationship between the arrector pili muscles, hair follicles, and the sympathetic nervous system.
  • The arrector pili muscles are attached to the hair follicles in the skin and are composed of smooth muscle fibers. These muscles are innervated by the sympathetic nervous system, which means that their contraction is triggered by the release of norepinephrine in response to various stimuli, such as cold, fear, or excitement. This anatomical relationship allows the arrector pili muscles to respond quickly to changes in the body's environment or emotional state, causing the hairs to stand upright and the skin to develop a bumpy appearance.
• Analyze the evolutionary significance of the arrector pili muscles and their role in the integumentary system's functions.
  • The arrector pili muscles and the phenomenon of piloerection they facilitate are believed to have evolved as a mechanism to help mammals, including humans, conserve body heat. By causing the hairs to stand upright, the arrector pili muscles trap air close to the skin, creating an insulating layer that helps retain body heat. This adaptation was likely crucial for the survival of early mammals in colder environments. Additionally, the ability of the arrector pili muscles to respond to emotional stimuli and alter the appearance of the skin may have played a role in social communication and the expression of emotions, which are important functions of the integumentary system.

Related terms

Piloerection: The erection or standing up of the hairs on the skin, often caused by the contraction of the arrector pili muscles.

Goosebumps: The bumpy appearance of the skin that results from the contraction of the arrector pili muscles, causing the hairs to stand upright.

Hair Follicle:

The structure in the skin that contains and supports the growth of a hair, and to which the arrector pili muscle is attached.