Extrafusal Intrafusal sợi cơ cơ trục chính sợi trục thần kinh cảm giác tim cơ tim sợi cơ Một ban nhạc Cross-striations hạt Glycogen H ban nhạc ban nhạc xen đĩa M ban nhạc Ti thể Myofibrils Myofilaments Nucleus Sarcomere | 94 Digital Histology FIGURE . Structure of thin and thick skin. Classification of Skin Based on the Thickness of the Epidermis Thin skin Covers entire body except palms and soles mm thick on the eyelid 5 mm thick on the back and shoulders Epidermis is thin mm thick but the dermis can be quite thick. Possesses hair with sebaceous glands Sweat glands are present. Thick glabrous skin Located on palms of the hands and soles of the feet thick Epidermis is thick. Hairless and thus possesses no sebaceous glands Sweat glands are present. Epidermis Cell types Keratinocytes. Keratinizing epidermal cells major cell type in the epidermis Melanocytes. Melanin pigment-producing cells Langerhans cells. Macrophages antigen-presenting cells 11. Skin 95 FIGURE . Comparison of epidermal layers in thick and thin skin. Layers of the epidermis and keratinization The epidermis is a stratified squamous keratinized dry epithelium. It is continually renewed every 15-30 days. Rapid cell proliferation occurs in the deepest layer stratum germinativum and daughter cells differentiate as they migrate toward the surface. This differentiation involves a process called keratinization which results in a variably thick layer of nonliving cellular husks at the surface of the epidermis. All cells in the epidermis that undergo the keratinization process are called keratinocytes. Layers of the epidermis Stratum germinativum basale . A single layer of cuboidal to columnar shaped cells that rest on the basement membrane and undergo rapid cell proliferation. These cells contain intermediate filaments composed of keratin. Stratum spinosum. Prickle-cell or spiny cell layer 3-10 cells thick. This layer is so-called because the cells are attached to one another by desmosomes and the cellular shrinkage resulting from fixation produces the spine-like structures. These cells accumulate bundles of keratin filaments called tonofibrils. Stratum granulosum two to four cells .
