The main structures of the hair follicle are the cuticle, the cortex, the medulla, the papilla and the matrix.
The cuticle is the outside, horny layer. It is composed of transparent, overlapping, protective cells. These cells connect with cells of the inner root sheath to stabilize the hair follicle. This layer has no pigment.
The cortex is the middle, or inner, layer, which gives strength and elasticity to the hair. It is made up of a fibrous substance formed by elongated cells. This layer contains pigment.
The medulla is the innermost layer referred to as the marrow of the hair. It is composed of round cells. The medulla may not be present is fine hair.
The papilla and matrix are also very important structures of the hair as the papilla is essential for the growth of hair and the matrix is the lower part of the bulb where mitosis takes place to produce the inner root sheath and the hair also.
Hair serves both as a physical protector for the epidermis and to insulate the skin. In areas where there is not a lot of sweating, the hair helps to hold and prevent the loss of sweat. Each hair follicle has a tiny muscle (the arrector pili) attached to it. This contracts when the body is cold making the hair stand up and causing goose-bumps at the surface of the skin where the hair follicles open. This process slows down the passage of air over the surface of the skin and helps maintain the warmth.