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Hair follicles are tubular structures located in the dermis, the layer of skin below the epidermis (the outermost layer of skin). Each hair follicle is paired with a tiny muscle called the arrector pili muscle. These arrector pili muscles, also known as hair erector muscles, are small muscles attached to hair follicles in mammals. They are responsible for piloerection, or goosebumps, when they contract and cause the hairs to stand on end.
| Characteristics | Values |
|---|---|
| Name of the hair muscle | Arrector pili muscle |
| Other names | Hair erector muscle |
| Location | Attached to hair follicles in mammals |
| Function | Makes the hair stand on end, known as piloerection or goosebumps |
| Composition | Bundle of smooth muscle fibres |
| Innervation | Sympathetic division of the autonomic nervous system |
| Contraction | Involuntary, stimulated by cold, fear, etc. |
| Primary function in mammals | Providing thermal insulation by trapping air between the erect hairs |
| Other functions | Stabilising the base of the hair follicle and forcing sebum along the hair follicle, protecting the hair |
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What You'll Learn
- The arrector pili muscle (APM) is responsible for making hair stand on end, known as piloerection or goosebumps
- The arrector pili muscle attaches to the base of the hair follicle on one end and to the upper layer of the dermis on the other
- Contraction of the arrector pili muscle is involuntary and can be stimulated by stress, cold, or fear
- The arrector pili muscle may cause sebum to be forced along the hair follicle, protecting the hair
- The arrector pili muscle stabilises the base of the hair follicle
The arrector pili muscle (APM) is responsible for making hair stand on end, known as piloerection or goosebumps
The arrector pili muscle (APM) is a tiny muscle attached to hair follicles in mammals. It is composed of a bundle of smooth muscle fibres that attach to several follicles (a follicular unit). The arrector pili muscle is responsible for making hair stand on end, known as piloerection or, colloquially, goosebumps. When the APM contracts, the hair stands up straight. This reaction is involuntary and can be stimulated by stressors such as cold temperatures or fear, which activate the sympathetic nervous system.
The piloerection response is believed to have a vestigial function related to fur. When the hair shafts of mammals stand on end, air becomes trapped between the hairs, helping the animal retain heat. This response can also serve to make an animal appear larger and more intimidating to rivals or predators. In humans, the APM likely serves a similar function, with body hair standing up when it is cold outside, creating a warming layer of air close to the body.
The arrector pili muscle also stabilises the base of the hair follicle and may cause sebum to be forced along the hair follicle towards the surface, protecting the hair. Skin conditions such as leprosy can damage the arrector pili muscles, preventing their contraction. Research has shown that inducing contraction of these muscles can reduce hair shedding due to traction alopecia.
The APM is not the only muscle associated with hair follicles. The dermal sheath, a smooth muscle surrounding hair follicles, has been found to contract during the follicle regression phase, relocating dermal papilla cells from the follicle base to the stem cells in the upper follicle. This contraction is believed to be essential to new hair growth.
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The arrector pili muscle attaches to the base of the hair follicle on one end and to the upper layer of the dermis on the other
The arrector pili muscle, also known as the hair erector muscle, is a tiny muscle attached to hair follicles in mammals. Each hair follicle is paired with an arrector pili muscle. This muscle attaches to the base of the hair follicle on one end and to the upper layer of the dermis on the other. When the arrector pili muscle contracts, the hair stands up straight, a phenomenon known as piloerection or "goosebumps". The arrector pili muscle is composed of a bundle of smooth muscle fibres that attach to several follicles (a follicular unit).
The arrector pili muscle is innervated by the sympathetic division of the autonomic nervous system. This means that its contraction is involuntary and can be stimulated by various stresses such as cold temperatures or fear. When an animal is cold, the arrector pili muscle helps to trap and preserve heat by causing the hairs to stand up straight. Similarly, when an animal is threatened, the arrector pili muscle can make the animal appear larger and more intimidating by raising its hairs. In addition to its role in temperature regulation and intimidation, the arrector pili muscle also stabilises the base of the hair follicle and may help to protect the hair by forcing sebum along the hair follicle towards the surface.
Research has shown that the arrector pili muscle is essential for new hair growth. During the follicle regression phase, the dermal sheath (a smooth muscle surrounding the hair follicle) contracts, physically relocating dermal papilla cells from the follicle base to the stem cells in the upper follicle. The dermal papilla provides essential signals for the activation of these stem cells, triggering the growth of a new hair shaft. Blocking the contraction of the dermal sheath has been shown to impede follicle regression and new hair shaft growth.
In certain skin conditions, such as leprosy, the arrector pili muscles can become damaged, preventing their contraction. Additionally, inducing contraction through an α1-adrenergic receptor agonist has been shown to reduce hair shedding associated with traction alopecia.
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Contraction of the arrector pili muscle is involuntary and can be stimulated by stress, cold, or fear
The arrector pili muscle is a small muscle attached to hair follicles in mammals. Each hair follicle is paired with one arrector pili muscle, which attaches to the base of the hair follicle on one end and to the upper layer of the dermis on the other. When the arrector pili muscle contracts, the hair stands up straight, resulting in what is commonly known as "goosebumps". This involuntary contraction of the arrector pili muscle can be stimulated by stress, cold, or fear.
The contraction of the arrector pili muscle has two main functions in mammals. Firstly, it helps to trap air between the erect hairs, providing thermal insulation and helping the animal retain body heat. This is particularly important in cold climates, as it helps to conserve heat. Secondly, when the hairs stand up, the animal appears larger and more intimidating to potential rivals or predators. This response to fear or threat is instinctual and serves as a defensive mechanism.
The arrector pili muscle is composed of a bundle of smooth muscle fibres that attach to several follicles, forming a follicular unit. The muscle attaches to the follicular stem cell niche in the follicular bulge, splitting at its deep end to encircle the follicle. The contraction of these muscles is involuntary and is controlled by the sympathetic division of the autonomic nervous system.
Research has also suggested that the arrector pili muscle plays a role in hair growth. In a study conducted by Mount Sinai researchers, it was found that the dermal sheath, a smooth muscle surrounding hair follicles, contracts during the follicle regression phase. This contraction helps relocate dermal papilla cells from the follicle base to the stem cells in the upper follicle, initiating the activation of stem cells and subsequent hair growth. While blocking the contraction of this muscle may not cure baldness caused by hair loss diseases, it could potentially help retain existing hair shafts before hair loss sets in.
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The arrector pili muscle may cause sebum to be forced along the hair follicle, protecting the hair
The arrector pili muscle, also known as the hair erector muscle, is a tiny muscle attached to hair follicles in mammals. Each hair follicle is paired with a sebaceous (oil) gland, which coats the hair to prevent dryness. The arrector pili muscle is also connected to the sebaceous gland at the hair follicle. When the arrector pili muscle contracts, it pulls the hair into a vertical position, forming small hillocks known as goosebumps. This contraction also aids in expelling the contents of the sebaceous gland.
The arrector pili muscle is composed of a bundle of smooth muscle fibres, which attach to several hair follicles. It is innervated by the sympathetic division of the autonomic nervous system, which means that its contraction is involuntary. Stresses such as cold temperatures or fear can stimulate the sympathetic nervous system, causing the arrector pili muscle to contract. This contraction has a principal function in providing thermal insulation for mammals. By making the hair stand erect, the muscle traps air between the hairs, helping the animal retain heat.
In addition to its role in thermal regulation, the contraction of the arrector pili muscle may also have another important function. The pressure exerted by the muscle during contraction can cause sebum, a natural oil produced by the sebaceous gland, to be forced along the hair follicle towards the surface. This sebum helps to protect the hair by keeping it lubricated and preventing dryness. It is important to note that the arrector pili muscles are absent from the hairs of the face, axilla, pubis, eyelashes, eyebrows, nostrils, and external auditory meatus in humans.
Overall, the arrector pili muscle plays a crucial role in maintaining the health and functionality of hair in mammals. Its ability to force sebum along the hair follicle provides protection and ensures that the hair remains moisturised and resilient.
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The arrector pili muscle stabilises the base of the hair follicle
The arrector pili muscle, also known as the hair erector muscle, is a tiny muscle attached to hair follicles in mammals. It is a bundle of smooth muscle fibres that attaches to the hair follicle on one end and to the upper layer of dermis on the other.
When the arrector pili muscle contracts, it pulls the hair into a vertical position, forming small hillocks known as goosebumps. This contraction also aids in the expulsion of the sebaceous gland's contents. The sebaceous gland sits at the angle between the muscle and the hair follicle.
The arrector pili muscle is believed to have a principal function in the majority of mammals, providing thermal insulation by increasing air-trapping between the erect hairs, thus helping the animal retain heat. However, in humans, the arrector pili muscle was thought to be vestigial, with a possible role in maintaining follicular integrity and stability. Recent studies have also explored its potential role in hair loss disorders.
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Frequently asked questions
Yes, there is a muscle called the arrector pili attached to each hair follicle.
The contraction of the arrector pili muscle makes the hair stand up, which is known as piloerection or getting "goosebumps".
Goosebumps are a vestigial function related to fur. Erecting the hair shafts helps to trap air, conserve heat in cold climates, and make the person/animal look bigger and more intimidating to rivals or predators.
Damage to the arrector pili muscles can prevent their contraction, and may lead to hair shedding or hair loss.
No, blocking the contraction cannot cure baldness caused by hair loss diseases. However, it can potentially prevent the loss of existing hair.
