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The arrector pili muscle, also known as the hair erector muscle, is a tiny muscle attached to hair follicles in mammals. When the arrector pili muscle contracts, it pulls the hair into a vertical position, causing it to stand on end, a phenomenon known as goose bumps. The arrector pili muscle is composed of smooth muscle fibres that attach to the hair follicle and extend towards the epidermis. These muscles are innervated by autonomic nerve fibres and play a role in thermoregulation by increasing air-trapping, which provides insulation.
| Characteristics | Values |
|---|---|
| Name | Arrector pili muscle (APM) |
| Description | A group of smooth muscle fibres that are connected to the connective tissue sheath of the hair follicle and extend towards the epidermis |
| Function | Moving the hair, causing it to stand on end (goose bumps or piloerection) |
| Innervation | Sympathetic division of the autonomic nervous system |
| Contraction | Involuntary; stimulated by stresses such as cold, fear, etc. |
| Primary Function | Providing thermal insulation by trapping air between erect hairs |
| Other Functions | Stabilising the base of the hair follicle, aiding the expulsion of the sebaceous gland's contents, potential role in maintaining follicular integrity and stability, possible role in hair loss disorders |
| Location | Absent from the hairs of the face, axilla, pubis, eyelashes, eyebrows, nostrils, and external auditory meatus |
| Structure | Fan-shaped; forked in hooved animals |
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What You'll Learn
- The arrector pili muscle is responsible for making hair stand on end
- Contraction of the arrector pili muscle aids the expulsion of the sebaceous gland's contents
- The arrector pili muscle is innervated by autonomic nerve fibres
- The arrector pili muscle is absent from facial hair, eyebrows, eyelashes, etc
- The arrector pili muscle may play a role in hair loss disorders
The arrector pili muscle is responsible for making hair stand on end
The arrector pili muscle, also known as the hair erector muscle, is a tiny muscle that attaches to hair follicles in mammals. When this muscle contracts, it pulls the hair into a vertical position, making the hair stand on end. This phenomenon is known colloquially as "goosebumps" or "goose flesh".
The arrector pili muscle is composed of a bundle of smooth muscle fibres that attach to several hair follicles. It originates in the papillary layer of the dermis and inserts into the hair follicle. The muscle is innervated by the sympathetic division of the autonomic nervous system, which can be stimulated by stresses such as cold temperatures or fear.
When the arrector pili muscle contracts, it not only pulls the hair upright but also elevates the epidermis where the hair enters. This contraction creates small hillocks on the skin, forming the characteristic goosebumps. Additionally, the arrector pili muscle plays a role in stabilising the base of the hair follicle and may aid in forcing sebum along the hair follicle towards the surface, protecting the hair.
The primary function of the arrector pili muscle in most mammals is to provide thermal insulation. When the hairs stand on end, air becomes trapped between them, helping the animal retain heat. While the arrector pili muscle was once thought to be vestigial in humans, recent studies have suggested that it may play a role in maintaining follicular integrity and stability, as well as influencing hair loss disorders.
In summary, the arrector pili muscle is responsible for making hair stand on end through its contraction, which has important implications for thermoregulation and potentially other physiological processes.
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Contraction of the arrector pili muscle aids the expulsion of the sebaceous gland's contents
The arrector pili muscle (APM) is a tiny muscle in the skin that attaches to hair follicles in mammals. When it contracts, it pulls the hair into a vertical position, forming small hillocks known as goose bumps. The contraction of the arrector pili muscle is involuntary and can be stimulated by various stresses, such as cold temperatures or fear. This response is an evolutionary conserved reaction to emotional disturbances, as Charles Darwin noted in 1872.
The arrector pili muscle is also involved in thermoregulation by contracting to increase air-trapping, providing thermal insulation for mammals. Additionally, it plays a role in maintaining the integrity of the follicular unit, which includes the hair follicle, sebaceous gland, and the arrector pili muscle itself. The sebaceous gland sits at the angle between the muscle and the hair follicle.
The contraction of the arrector pili muscle aids in the expulsion of the sebaceous gland's contents, known as sebum, into the hair follicle canal. This process helps maintain the skin's lipid barrier, protecting the hair and skin from water loss and microbial invasion. The muscle's rhythmic activity may regulate sebum flow, preventing follicular duct occlusion and sebaceous gland dysfunction.
The integrity of the arrector pili muscle is important for maintaining healthy sebaceous gland function. Research suggests that as muscle integrity decreases with age or disease, sebum production is affected. Additionally, muscle degeneration may contribute to inflammatory skin conditions, such as hidradenitis suppurativa, by preceding glandular obstruction and inflammatory lesion development.
In summary, the contraction of the arrector pili muscle aids the expulsion of the sebaceous gland's contents, known as sebum, which has protective functions for the hair and skin. This process is integral to maintaining skin health and preventing certain skin conditions.
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The arrector pili muscle is innervated by autonomic nerve fibres
The arrector pili muscle, also known as the hair erector muscle, is a tiny muscle that attaches to hair follicles in mammals. It is composed of a bundle of smooth muscle fibres which attach to several follicles (a follicular unit). The arrector pili muscle is innervated by autonomic nerve fibres, specifically the sympathetic division of the autonomic nervous system. This means that it is controlled by the unconscious part of the nervous system, and its contraction is involuntary.
The arrector pili muscle originates in the papillary layer of the dermis and inserts on the outer root sheath of the follicle, just below the sebaceous gland. The muscle attaches to the follicular stem cell niche in the follicular bulge, and splits at its deep end to encircle the follicle. When the arrector pili muscle contracts, it pulls the hair into a vertical position, forming goose bumps (piloerection). This contraction is often stimulated by stress, such as cold temperatures or fear, which activates the sympathetic nervous system.
The arrector pili muscle has several functions. Firstly, it helps to stabilise the base of the hair follicle. Secondly, it aids in thermoregulation by contracting to increase air-trapping between the erect hairs, which provides thermal insulation. Finally, the contraction of the arrector pili muscle may also cause sebum to be forced along the hair follicle, protecting the hair and reducing hair shedding.
Recent studies have also suggested that the arrector pili muscle may play a role in hair loss disorders, particularly in the development of androgenetic alopecia, the most common cause of human hair loss. By understanding the anatomy and physiology of the arrector pili muscle, researchers can explore its potential role in maintaining follicular integrity and stability, and develop new models to explain hair loss.
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The arrector pili muscle is absent from facial hair, eyebrows, eyelashes, etc
The arrector pili muscle is a tiny smooth muscle of the skin that connects the hair follicle to the connective tissue of the basement membrane. The arrector pili muscle is responsible for moving the hair, causing it to stand on end, which is known colloquially as goose bumps or goose flesh. The arrector pili muscle is innervated by the sympathetic division of the autonomic nervous system, and its contraction is involuntary.
The arrector pili muscle is absent from the hairs on the human face, including the eyebrows, eyelashes, and nostrils. It is also absent from the hairs in the axilla (armpit), pubis, and external auditory meatus (ear canal). These areas of the body contain sexual hairs, which are found in the beard and pubic regions. Sexual hairs do not have arrector pili muscles.
The arrector pili muscle has a role in thermoregulation by contracting to increase air-trapping, which provides insulation. This function is particularly important for the majority of mammals, as it helps them retain heat. However, the arrector pili muscle was thought to be vestigial in humans, as we have other means of regulating our body temperature.
Recent studies have suggested that the arrector pili muscle may play a role in maintaining the integrity and stability of the hair follicle. This muscle may also be involved in the hair cycle, wound healing, and the development of hair loss disorders such as androgenetic alopecia.
The absence of the arrector pili muscle from the facial hair, eyebrows, eyelashes, and other areas of the body may be due to the specialized functions of these hairs. For example, the hair in the nostrils and around the eyes helps to trap and exclude dust particles, allergens, and microbes, while the eyebrows prevent sweat and other particles from dripping into the eyes. The absence of the arrector pili muscle in these areas may allow for more precise and controlled movements of these hairs.
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The arrector pili muscle may play a role in hair loss disorders
The arrector pili muscle (APM) is a tiny muscle in the skin that connects the hair follicle to the connective tissue of the basement membrane. When the APM contracts, it pulls the hair into a vertical position, causing goose bumps. The APM also stabilises the base of the hair follicle and aids the expulsion of the sebaceous gland's contents.
Recent studies have investigated the potential role of the APM in hair loss disorders. For example, the APM has been shown to lose attachment to secondary follicles in herald units, remaining attached only to the primary follicles. This miniaturisation of secondary follicles and detachment of the APM continues until all follicular units are affected, eventually resulting in baldness. Torkamani et al. have also proposed that the APM undergoes fat degeneration in irreversible hair loss conditions, such as advanced androgenic alopecia (AGA).
In addition, the loss of the APM could result in an altered angle between the isthmus and infundibulum, causing the retention of shed telogen hairs. Inducing contraction of the APM via an α1-adrenergic receptor agonist has been shown to reduce hair shedding as a result of traction alopecia.
The APM may also play a role in the development of androgenetic alopecia, the most common cause of human hair loss. However, it remains unclear exactly how APM degeneration and fat infiltration are related to follicle miniaturisation and hair loss.
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Frequently asked questions
The arrector pili muscle, also known as the hair erector muscle, is the muscle that controls hair.
The arrector pili muscle contracts, causing the hair to stand on end, forming goose bumps. This muscle is also responsible for mediating thermoregulation by contracting to increase air-trapping.
The arrector pili muscle is a tiny smooth muscle of the skin that extends from the papillary layer of dermis to a hair follicle.
