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The arrector pili muscles, also known as hair erector muscles, are small muscles attached to hair follicles in mammals. They are located in the dermis, along with other appendageal structures of the skin, including the hair follicle, sebaceous gland, and apocrine gland. When the arrector pili muscles contract, they cause the hairs to stand on end, resulting in what is commonly known as goose bumps. This contraction is involuntary and can be stimulated by various stresses such as cold temperatures or fear, activating the sympathetic nervous system. The primary function of these muscle contractions in most mammals is to provide thermal insulation by trapping air between the erect hairs, helping the animal retain heat.
| Characteristics | Values |
|---|---|
| Common Name | Erector Pili Muscle |
| Scientific Name | Arrector Pili Muscle (APM) |
| Type | Small, fan-shaped smooth muscles |
| Location | Attached to hair follicles in mammals |
| Function | Causes hair to stand on end (goose bumps) |
| Controlled By | Sympathetic branch of the autonomic nervous system |
| Contraction | Involuntary; stimulated by stress, cold, fear |
| Purpose | Provides thermal insulation in mammals |
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What You'll Learn
The arrector pili muscle is attached to hair follicles
The arrector pili muscle, also known as the hair erector muscle, is a small muscle attached to hair follicles in mammals. Each arrector pili muscle is composed of a bundle of smooth muscle fibres that attach to several hair follicles, forming what is known as a follicular unit. The arrector pili muscle attaches to the follicular stem cell niche in the follicular bulge, which is considered the site where new matrix cells are formed and the hair growth cycle is initiated. At their deep end, these muscles split to encircle the follicle.
The arrector pili muscle is innervated by the sympathetic division of the autonomic nervous system. The contraction of these muscles is involuntary and is caused by various stresses, such as cold temperatures or fear, stimulating the sympathetic nervous system. When the arrector pili muscle contracts, the hair stands on end, creating the appearance of goose bumps. This response is known as piloerection.
In addition to inducing goose bumps, the contraction of the arrector pili muscle serves a critical function in most mammals. When the hairs are erect, air becomes trapped between them, providing essential thermal insulation. This mechanism helps the animal retain heat.
The arrector pili muscle also plays a role in wound healing and the development of androgenetic alopecia, the most common cause of human hair loss. Recent studies have investigated the potential role of the arrector pili muscle in maintaining follicular integrity and stability.
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Contraction of the muscle causes hair to stand on end
The arrector pili muscles, also known as hair erector muscles, are small, fan-shaped muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end, known as goose bumps or piloerection. Each arrector pili muscle is composed of a bundle of smooth muscle fibres that attach to several hair follicles. The arrector pili muscles are innervated by the sympathetic division of the autonomic nervous system. The muscle attaches to the follicular stem cell niche in the follicular bulge, splitting at their deep end to encircle the follicle.
The contraction of the arrector pili muscles is involuntary and is often stimulated by stress or fear. For example, when the body surface is chilled, the arrector pili muscles contract and erect the hairs, producing goose bumps. This response helps to trap air between the erect hairs, providing thermal insulation and helping the body retain heat. Similarly, in response to cold temperatures, muscle-anchored nerves form "synapse-like" connections with hair follicle stem cells to promote hair regeneration.
In addition to temperature regulation, the contraction of the arrector pili muscles can also be induced through the use of certain chemicals. For example, inducing contraction via an α1-adrenergic receptor agonist has been shown to reduce hair shedding as a result of traction alopecia. However, skin conditions such as leprosy can damage these muscles, preventing their contraction and potentially leading to hair loss.
The term "arrector pili" originates from Latin and translates to "hair erector". This aptly describes the function of these muscles, which are responsible for causing hair to stand on end when contracted.
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The muscle is composed of smooth muscle fibres
The arrector pili muscles, or hair erector muscles, are small muscles attached to hair follicles in mammals. They are composed of smooth muscle fibres, which are bundled together and attached to several hair follicles. These smooth muscle fibres are fan-shaped and are associated with the base of each hair. When the body surface is chilled, or in response to other stimuli such as fear, the arrector pili muscles contract, causing the hairs to stand on end. This process is known as piloerection, and it results in the appearance of goose bumps on the skin.
The contraction of the arrector pili muscles is involuntary and is stimulated by the sympathetic nervous system. When contracted, the muscles pull the hairs erect, compressing an oil gland above each muscle. This contraction has a principal function of providing thermal insulation in mammals. The air trapped between the erect hairs helps the animal retain heat.
The arrector pili muscles are innervated by the sympathetic division of the autonomic nervous system. They attach to the follicular stem cell niche in the follicular bulge, splitting at their deep end to encircle the hair follicle. This attachment allows for the involuntary contraction of the muscles, causing the hairs to stand up and create goose bumps.
The term "arrector pili" comes from the Latin translation of "hair erector". These muscles play a crucial role in the body's response to various stimuli, such as cold temperatures or fear, by inducing piloerection and providing insulation. The smooth muscle fibres that make up the arrector pili muscles are essential for this process, allowing mammals to retain heat and adapt to their environment.
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Contraction of the muscle is involuntary
The arrector pili muscles, also known as hair erector muscles, are small, fan-shaped muscles attached to hair follicles in mammals. They are composed of a bundle of smooth muscle fibres which attach to several follicles (a follicular unit).
The contraction of the arrector pili muscles is involuntary. This means that the muscle contraction is not under conscious control. However, it can be stimulated by the sympathetic nervous system, which is activated in response to various stresses such as cold temperatures, fear, or worry.
When the arrector pili muscles contract, the hairs stand on end, resulting in what is commonly known as goose bumps or piloerection. This contraction also compresses an oil gland above each muscle, causing the secretion of an oily substance called sebum, which helps prevent hair and skin from drying out.
The primary function of arrector pili muscle contraction in most mammals is to provide thermal insulation. When the hairs stand on end, air becomes trapped between them, helping the animal retain heat. This mechanism is particularly important for mammals with thick fur, as it allows them to increase their body temperature in cold environments.
In humans, the arrector pili muscles are thought to be vestigial, meaning they have lost their original function. However, recent studies have suggested that these muscles may still play a role in maintaining follicular integrity and stability, as well as in sebum secretion and wound healing. Additionally, there is ongoing research into the potential role of the arrector pili muscles in hair loss disorders, such as traction alopecia and androgenetic alopecia, which is the most common cause of human hair loss.
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The principal function of the muscle is to provide insulation
The arrector pili muscles, also known as hair erector muscles, are small muscles attached to hair follicles in mammals. They are composed of a bundle of smooth muscle fibres which attach to several follicles (a follicular unit). Each arrector pili muscle is associated with the base of a hair and contracts when the body surface is chilled, causing the hair to stand on end. This phenomenon is known colloquially as goose bumps or piloerection.
The contraction of the arrector pili muscles is involuntary and is stimulated by the sympathetic nervous system. Stresses such as cold temperatures, fear, or worry can activate this system, causing the muscles to contract. This contraction has a principal function in the majority of mammals: providing insulation. When the hairs stand erect, air becomes trapped between them, helping the animal retain heat. This mechanism aids in thermoregulation, ensuring the mammal maintains a suitable body temperature despite external cold temperatures.
The arrector pili muscle's role in insulation is particularly crucial for mammals with thicker coats, such as certain breeds of dogs and cats. In these animals, the contraction of the arrector pili muscles can result in a noticeable visual change in the coat's appearance, making it seem fuller or fluffier. This response not only aids in heat retention but also helps create a protective barrier against the cold, making it more challenging for cold air to reach the animal's skin directly.
Additionally, the compression of oil glands above each muscle during contraction may also contribute to insulation. The activation of the arrector pili muscles can compress these glands, releasing oils that help condition and waterproof the hair. This process ensures that the coat remains relatively dry and effective at trapping body heat, further enhancing the animal's insulation.
In summary, the principal function of the arrector pili muscle is to provide insulation in mammals. This is achieved through the erection of hairs, trapping air, and facilitating heat retention. The muscle's response to stimuli such as cold temperatures is essential for the survival of many mammals, enabling them to maintain a stable body temperature even in challenging environmental conditions.
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Frequently asked questions
Erector pili muscles, also known as arrector pili muscles, are small, fan-shaped muscles attached to hair follicles in mammals.
When the muscles contract, they cause the hair to stand on end, creating what is commonly known as "goosebumps". Their principal function in most mammals is to provide insulation by trapping air between the erect hairs, helping the animal retain heat.
Stresses such as cold temperatures, fear, or worry can stimulate the sympathetic nervous system, causing the erector pili muscles to contract. The contraction of these muscles is involuntary and cannot be controlled consciously.
Yes, skin conditions such as leprosy can damage the erector pili muscles, preventing them from contracting.
