Arrector muscles

The appendages of skin are hair follicles, sebaceous glands, eccrine and apocrine sweat glands, hair, nails, and arrector pili muscles. 

Appendageal structures commonly found within the skin are the hairs, hair follicles, associated sebaceous glands, apocrine and eccrine sweat glands, and arrector pili muscles. Hairs are formed by epidermal invaginations. These keratinized structures traverse the dermis and may extend into the hypodermis. The free part of the hair above the surface of the skin is the hair shaft, and the part deep within the dermis is the hair root, which forms an expanded knob-like structure called the hair bulb. This is composed of a matrix of epithelial cells in different stages of differentiation. Hair is composed of three concentric epithelial cell layers the outermost thin cuticle, a densely packed keratinized cortex, and a central medulla of cuboidal cells. The hair follicle consists of four major components (1) internal root sheath (internal root sheath cuticle, granular layer, pale epithelial layer) (2) external root sheath (several layers similar to the epidermis) (3) dermal papilla (connective tissue) and (4) hair matrix (comparable to the stratum basale of the epidermis). 

Sebaceous gland Arrector pill muscle Connective tissue sheath... 

The arrector piK muscle is under adrenergic control and does not respond to a local increase in ACh concentration. The fibroblasts and myofibroblasts are very interesting cells as far as the possibilities of the action of DMAE is concerned. Eibroblasts have cytoplasmic myofilaments that help them move in the dermis when necessary. There are different types of fibroblast subpopulations. Some authors maintain that these different subpopulations expand when they are needed through different phenotype expressions, whereas others believe that these subpopulations coexist permanently in the dermis. These two hypotheses are not incompatible. Myofibroblasts (MEBs) are phenotypicaUy modified fibroblasts that have the secretory capacity of fibroblasts, which helps them synthesize strong fibronectin fibers. They express the phenotypic characteristics of nonmuscle cells, but with the contractile capacities (of SMCs) that make them responsible for most of the phenomena of fibrotic contraction in the body. The fibronectin fibers syn-... 

Sebaceous gland Arrector p muscle Connectr tissue sheath External root sheath Internal root sheath Apocri sweat gland Matri ... 

Associated with most hair follicles are bundles of smooth muscle called the arrector pili muscle. This muscle attaches to the dermal root sheath of the hair follicle and extends toward the epidermis, where it connects to the papillary layer of the dermis. On contraction, this muscle not only erects the hairs but also plays a role in emptying the sebaceous glands. 

Fig. 2.10 Pilosebaceous follicle with arrector pUi muscle. Hematoxylin-phloxine-saffron stain. Obj x20...

---