Answer
Hairs are one of the set of skin accessory structures. They may have different appearances on different parts of the body, but the general structure it comprises the following parts:
Shaft, root, follicle, bulb, papilla and matrix
The shaft is the part we usually mean when we use the term "hair" in lay vernacular. This is the part of the hair that is visible above the surface of the epidermis. It is made up of a number of dead keratinized cells held together by cell secretions. The root of the hair is the part below the surface --in the lower epidermis and in dermis. It lies in a hair follicle and expands to form an indented bulb.
The shaft is composed of three layers of cells --outer to inner : the cuticle-- a layer of squamous highly keratinized cells; the middle layer of long cells is the cortex ; the innermost layer or medulla of irregular cells which may be pigmented to various degrees.
Beneath the epidermis the hair root is surrounded by the follicle. This is composed of an external root sheath and an external epithelial root sheath; these together constitute the epithelial root sheath . Where the dermis surrounds the hair follicle, it forms a dermal root sheath.
The bulb is formed by the base of the hair follicle and the root sheath is formed by the dermis. The bottom of the bulb is usually indented, and in this indentation are found blood vessels that carry nutrients to the hair, areolar connective tissue, and germinal matrix cells that derive from the stratum basale of the epidermis. The cells of the matrix divide to maintain growing hairs and to produce new hairs to replace dead ones.
Work Step by Step
Goose flesh or goose bumps are small elevations of the skin around hair shafts that form when one is cold or fearful. There are small muscles around the hair follicles--the arrector pili muscles; the apparent physiological function of these muscles is to pull recumbent hairs into upright positions to form a layer of hair to enhance insulation --when one is clod. The stimulus of cold activates the sympathetic system (ANS), and the sympathetic stimulation of the arrector pili causes them to contract. The contraction of the muscles raise the hairs, and also elevates areas of the skin ( dermal papillae) around the bottom of the hair shafts. This happens all over the skin, not not only in cold weather, but in emotional situations such as when one is fearful or very excited. This layer of bumpy shin is what is called "goose flesh."
