Additional images
Insertion of sebaceous glands into hair shaft
Cross-section of all skin layers
| Details | |
|---|---|
| Nerve | Sympathetic postganglionic nerve fibers |
| Identifiers | |
| TA98 | A16.0.00.024 |
| TA2 | 7051 |
| TH | H3.12.00.3.01041 |
| FMA | 67821 |
| Anatomical terms of muscle | |
The arrector pili muscles, also known as hair erector muscles, [1] are small muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end, [2] known colloquially as goose bumps (piloerection). [3]
Each arrector pili is composed of a bundle of smooth muscle fibres which attach to several follicles (a follicular unit). [4] Each is innervated by the sympathetic division of the autonomic nervous system. [4] The muscle attaches to the follicular stem cell niche in the follicular bulge, [3] [4] [5] splitting at their deep end to encircle the follicle. [6]
The contraction of the muscle is involuntary. Stresses such as cold, fear etc. may stimulate the sympathetic nervous system, and thus cause muscle contraction. [4]
Contraction of arrector pili muscles have a principal function in the majority of mammals of providing thermal insulation. [4] Air becomes trapped between the erect hairs, helping the animal retain heat.
Many animals experience contraction of the arrector pili muscle in response to a perceived threat. This helps the animal seem more larger and more intimidating as a result. [7]
Pressure exerted by the muscle may cause sebum to be forced along the hair follicle towards the surface, protecting the hair. [8]
Arrector pili muscles also stabilise the base of the hair follicle. [5] [6]
Skin conditions such as leprosy can damage arrector pili muscles, preventing their contraction. [9] Inducing contraction of the arrector pili muscles via an α1-adrenergic receptor agonist has been shown to reduce hair shedding as a result of traction alopecia [10]
The term "arrector pili" comes from Latin. It translates to "hair erector". [1]
Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.
Alopecia areata, also known as spot baldness, is a condition in which hair is lost from some or all areas of the body. It often results in a few bald spots on the scalp, each about the size of a coin. Psychological stress and illness are possible factors in bringing on alopecia areata in individuals at risk, but in most cases there is no obvious trigger. People are generally otherwise healthy. In a few cases, all the hair on the scalp is lost, or all body hair is lost. Hair loss can be permanent, or temporary.
Hair loss, also known as alopecia or baldness, refers to a loss of hair from part of the head or body. Typically at least the head is involved. The severity of hair loss can vary from a small area to the entire body. Inflammation or scarring is not usually present. Hair loss in some people causes psychological distress.
Sebaceous hyperplasia is a disorder of the sebaceous glands in which they become enlarged, producing flesh-colored or yellowish, shiny, often umbilicated bumps. Sebaceous hyperplasia, primarily affecting older patients in high-concentration areas like the face, head, and neck, typically has a 2-4 mm diameter and causes no symptoms. The lesions are often surrounded by telangiectatic blood vessels, also known as "crown vessels," and a central dell, which is in line with the origin of the lesions.
The hair follicle is an organ found in mammalian skin. It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. The hair follicle regulates hair growth via a complex interaction between hormones, neuropeptides, and immune cells. This complex interaction induces the hair follicle to produce different types of hair as seen on different parts of the body. For example, terminal hairs grow on the scalp and lanugo hairs are seen covering the bodies of fetuses in the uterus and in some newborn babies. The process of hair growth occurs in distinct sequential stages: anagen is the active growth phase, catagen is the regression of the hair follicle phase, telogen is the resting stage, exogen is the active shedding of hair phase and kenogen is the phase between the empty hair follicle and the growth of new hair.
A sebaceous gland or oil gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest number on the face and scalp, but also on all parts of the skin except the palms of the hands and soles of the feet. In the eyelids, meibomian glands, also called tarsal glands, are a type of sebaceous gland that secrete a special type of sebum into tears. Surrounding the female nipples, areolar glands are specialized sebaceous glands for lubricating the nipples. Fordyce spots are benign, visible, sebaceous glands found usually on the lips, gums and inner cheeks, and genitals.
A skin condition, also known as cutaneous condition, is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, nails, and related muscle and glands. The major function of this system is as a barrier against the external environment.
Goose bumps, goosebumps or goose-pimples are the bumps on a person's skin at the base of body hairs which may involuntarily develop when a person is tickled, cold or experiencing strong emotions such as fear, euphoria or sexual arousal.
Hyperkeratinization is a disorder of the cells lining the inside of a hair follicle. It is the normal function of these cells to detach or slough off from the skin lining at normal intervals. The dead cells are then forced out of the follicle. However, in hyperkeratinization, this process is interrupted and a number of these dead skin cells do not leave the follicle because of an excess of keratin, a natural protein found in the skin. This excess of keratin, which is influenced by genetics, results in an increased adherence/bonding of dead skin cells together. This cohesion of cells will block or "cap" the hair follicle or clog the sebaceous/oil duct. Pathogens may also play a role in causing, perpetuating, or simply taking advantage of this phenomenon, such as virulent sub-strains of Cutibacterium acnes and irregular migration of Staphylococcus epidermidis from the outer surface of the skin into the follicle, where commensal strains of C. acnes exclusively habitate. It itches mildly at times, and strongly at others. Very often it cannot be felt at all.
The management of hair loss, includes prevention and treatment of alopecia, baldness, and hair thinning, and regrowth of hair.
Pattern hair loss is a hair loss condition that primarily affects the top and front of the scalp. In male-pattern hair loss (MPHL), the hair loss typically presents itself as either a receding front hairline, loss of hair on the crown and vertex of the scalp, or a combination of both. Female-pattern hair loss (FPHL) typically presents as a diffuse thinning of the hair across the entire scalp.
An apocrine sweat gland is composed of a coiled secretory portion located at the junction of the dermis and subcutaneous fat, from which a straight portion inserts and secretes into the infundibular portion of the hair follicle. In humans, apocrine sweat glands are found only in certain locations of the body: the axillae (armpits), areola and nipples of the breast, ear canal, eyelids, wings of the nostril, perineal region, and some parts of the external genitalia. Modified apocrine glands include the ciliary glands in the eyelids; the ceruminous glands, which produce ear wax; and the mammary glands, which produce milk. They are distinct from eccrine sweat glands, which cover the whole body.
Pili torti is characterized by short and brittle hairs that appear flattened and twisted when viewed through a microscope.
Madarosis is a condition that results in the loss of eyelashes, and sometimes eyebrows. The term "madarosis" is derived from the ancient Greek "madaros", meaning "bald". It originally was a disease of only losing eyelashes but it currently is the loss of both eyelashes and eyebrows. Eyebrows and eyelashes are both important in the prevention of bacteria and other foreign objects from entering the eye. A majority of patients with madarosis have leprosy, and it was reported that 76% of patients with varying types of leprosy had madarosis.
Scarring hair loss, also known as cicatricial alopecia, is the loss of hair which is accompanied with scarring. This is in contrast to non scarring hair loss.
Central centrifugal cicatricial alopecia (CCCA), is a type of alopecia first noticed in African Americans in the 1950s and reported by LoPresti et al. in 1968 as a result of application of petrolatum followed by a stove-heated iron comb. The original theory was that the hot petrolatum would travel down to the hair root, burn the follicle, and after repetitive injury scarring would result. Later CCCA was realized to affect men and women without a history significant for use of such styling techniques. Consequently, the terms "follicular degeneration syndrome" per Sperling and Sau in 1992 and then CCCA per Olsent et al. in 2003 were evolved. Plausible contributing factors may include other African-American styling techniques such as relaxers, tight braids, heavy extensions, certain oils, gels or pomades.
Congenital smooth muscle hamartoma is typically a skin colored or lightly pigmented patch or plaque with hypertrichosis. Congenital smooth muscle hamartoma was originally reported in 1969 by Sourreil et al.
Alopecia mucinosa, also known as Follicular mucinosis, Mucinosis follicularis, Pinkus' follicular mucinosis, and Pinkus' follicular mucinosis–benign primary form, is a skin disorder that generally presents, but not exclusively, as erythematous plaques or flat patches without hair primarily on the scalp, neck and face. This can also be present on the body as a follicular mucinosis and may represent a systemic disease.
Hackles are the erectile plumage or hair in the neck area of some birds and mammals.
Hair follicle nevus is a cutaneous condition that presents as a small papule from which fine hairs protrude evenly from the surface.
