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The arrector pili muscle, also known as the hair erector muscle, is a small muscle attached to hair follicles in mammals. The contraction of these muscles causes the hair to stand up, resulting in what is commonly known as goose bumps. The arrector pili muscle has a principal function in providing thermal insulation to mammals. The contraction of these muscles can be stimulated by various factors, such as cold temperatures, fear, or other stressors, and can also be influenced by the sympathetic nervous system.
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What You'll Learn
The arrector pili muscle's role in hair loss
The arrector pili muscle (APM), also known as the hair erector muscle, is a small band of smooth muscle that connects the hair follicle to the connective tissue of the basement membrane. The APM is attached to the follicular stem cell niche in the follicular bulge, splitting at its deep end to encircle the follicle. The contraction of the APM is involuntary and is caused by various stresses, such as cold temperatures or fear, which stimulate the sympathetic nervous system. This contraction causes the hairs to stand on end, resulting in goose bumps (piloerection).
The APM has a principal function in providing thermal insulation for mammals. When the hairs stand on end, air becomes trapped between them, helping the animal retain heat. Additionally, the contraction of the APM in response to a perceived threat can make the animal seem larger and more intimidating. The pressure exerted by the muscle also helps protect the hair by forcing sebum along the hair follicle towards the surface.
Recent studies have suggested that the APM may play a role in maintaining follicular integrity and stability. There is also a potential link between the APM and hair loss disorders, with proposed models explaining APM changes in hair loss. For example, in scarring alopecia, inflammation or injury damages the epithelial stem cell population in the bulge, leading to the destruction of the entire follicular unit. Torkamani et al. have proposed that the APM undergoes fat degeneration in irreversible hair loss conditions such as advanced androgenic alopecia (AGA).
Inducing contraction of the APM via an α1-adrenergic receptor agonist has been shown to reduce hair shedding due to traction alopecia. This suggests that the APM may have a role in preventing certain types of hair loss. Overall, while the APM's primary role is in thermoregulation and protection, its potential involvement in hair loss disorders is an area of ongoing research.
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How the arrector pili muscle causes goose bumps
The arrector pili muscle, also known as the hair erector muscle, is a bundle of smooth muscle fibres attached to hair follicles in mammals. The contraction of these muscles causes the hair to stand up, resulting in what is colloquially known as goose bumps.
Each arrector pili muscle is composed of a bundle of smooth muscle fibres that attach to several hair follicles. These muscles are innervated by the sympathetic division of the autonomic nervous system. The arrector pili muscle attaches to the follicular stem cell niche in the follicular bulge, splitting at its deep end to encircle the follicle. This contraction of the muscle is involuntary and is often stimulated by the sympathetic nervous system in response to stress or cold.
When the body surface is chilled, the arrector pili muscles contract and erect the hairs. This contraction also compresses the oil gland above each muscle, forcing sebum along the hair follicle towards the surface, which protects the hair. The principal function of this process in mammals is to provide thermal insulation by trapping air between the erect hairs, helping the animal retain heat.
The arrector pili muscle also plays a role in how animals respond to threats. When an animal perceives a threat, the arrector pili muscle contracts, causing the hair to stand on end and making the animal appear larger and more intimidating.
In addition to its role in thermoregulation and intimidation, the arrector pili muscle has been studied for its potential involvement in hair loss disorders. Research suggests that changes in the arrector pili muscle may contribute to hair loss conditions such as alopecia.
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The arrector pili muscle's response to threats
The arrector pili muscles, also known as hair erector muscles, are small muscles attached to hair follicles in mammals. Each arrector pili is composed of a bundle of smooth muscle fibres that attach to several follicles (a follicular unit). The arrector pili muscles are innervated by the sympathetic division of the autonomic nervous system. The contraction of these muscles is involuntary and is caused by various stressors, such as cold temperatures and fear, which stimulate the sympathetic nervous system.
When an animal perceives a threat, the arrector pili muscles contract, causing the hairs to stand on end. This response is often referred to as "goose bumps" or "piloerection". The contraction of the arrector pili muscles has an important function: it helps the animal seem larger and more intimidating to potential predators. This response is particularly useful for animals with fur, as the erect hairs trap air, providing an insulating air layer near the skin and reducing heat loss.
In addition to responding to threats, the arrector pili muscles also play a role in thermoregulation. By altering the position of the hair shaft, these muscles can influence skin blood flow and regulate body temperature. For example, in cold environments, the arrector pili muscles contract, reducing blood flow to the skin's surface and preventing heat loss.
Furthermore, the contraction of the arrector pili muscles exerts pressure on the sebaceous glands, facilitating the expulsion of sebum into the hair follicle canal. This process helps to maintain the skin's lipid barrier, protecting against water loss and microbial invasion.
The arrector pili muscles have a unique shape and attachment site, suggesting they play a significant role in maintaining follicular integrity. These muscles encircle the follicular unit and attach to the primary hair follicle in the bulge, contributing to the structural support and stability of the hair follicle.
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The muscle's stabilisation of hair follicles
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 bundles of smooth muscle fibres which attach to several follicles (a follicular unit). 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 follicle.
The contraction of the arrector pili muscles is involuntary and is caused by various stressors such as cold temperatures or fear. This contraction causes the hairs to stand on end, resulting in goose bumps (piloerection). This response serves a protective function by helping the animal to retain heat through the trapping of air between the erect hairs. Additionally, the contraction may force sebum along the hair follicle towards the surface, providing further protection to the hair.
The arrector pili muscles also play a role in stabilising the base of the hair follicle. Skin conditions, such as leprosy, can damage these muscles and impair their ability to contract. Inducing contraction of the arrector pili muscles has been shown to reduce hair shedding associated with traction alopecia.
The presence of epithelial stem cells in the human hair bulge has been confirmed, and these cells are believed to contribute to wound healing. Major changes in the arrector pili muscles have been observed in certain skin conditions, yet the function of piloerection is maintained even when the muscle attachment site is displaced.
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The muscle's contraction in cold conditions
The arrector pili muscles, also known as hair erector muscles, are small, fan-shaped muscles attached to hair follicles in mammals. When the body surface is chilled, these muscles contract and cause the hair to stand on end, leading to what is colloquially known as "goosebumps". This involuntary contraction is caused by the stimulation of the sympathetic nervous system due to stress factors such as cold or fear. The primary function of this response in mammals is to provide thermal insulation by trapping air between the erect hairs, helping the body retain heat.
In colder weather, the rate at which oxygen is released from haemoglobin to the muscles decreases, resulting in reduced oxygen availability for muscle function. This leads to feelings of stiffness and discomfort, as oxygen is essential for fuelling the muscles. To compensate for this decrease in oxygen availability, it is beneficial to increase oxygen intake through regular stretching and exercise. Active stretching improves blood circulation, providing oxygen-rich blood and essential nutrients to the muscles, thereby enhancing their function, strength, and flexibility.
Cold temperatures have been shown to reduce muscle strength and contractile speed in humans, impairing exercise performance. This effect is attributed to the influence of temperature on the activation of myosin motors in skeletal muscles. Lower temperatures disrupt the helical arrangement of myosin, resulting in a reduced number of motors in the "ON" state capable of binding actin upon stimulation. This disordered state of myosin motors impairs muscle contraction and reduces the force generated.
However, it is important to note that the impact of temperature on muscle performance may vary depending on the species and muscle type. For example, in frog muscles, the number of actin-attached motors during an isometric contraction remains unchanged between 0°C and 20°C. In contrast, mouse muscles exhibit a threefold decrease in force generation at 10°C compared to physiological temperatures.
Additionally, muscle cooling has been associated with increased muscle activity, indicating a potential increase in neural drive due to alterations in motor unit recruitment. This increased muscle activity may be a compensatory mechanism to maintain overall muscle performance during cold conditions.
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Frequently asked questions
A pili muscle, or arrector pili muscle, is a small, fan-shaped smooth muscle attached to hair follicles in mammals.
When the body's surface is chilled, or in response to a perceived threat, the pili muscle contracts and pulls the hairs erect, causing goose bumps.
The contraction of the pili muscle has a principal function of providing thermal insulation to help the body retain heat. It can also make an animal seem larger and more intimidating when threatened.
The pili muscle may have a role in hair loss disorders, with changes in the pili muscle observed in alopecia. Inducing contraction of the pili muscle has been shown to reduce hair shedding due to traction alopecia.
