Final answer:
The medulla, cortex, and cuticle constitute the three layers of the hair shaft, contributing to hair's texture, strength, and protection.
Step-by-step explanation:
The medulla, cortex, and cuticle make up the hair shaft. The medulla is the central core, surrounded by the cortex, which is a layer of compressed cells, and the outermost layer is the cuticle, which is composed of hard cells.
The medulla, cortex, and cuticle are the three layers that make up the hair shaft. The medulla is the innermost layer, and it forms the central core of the hair, but not all hair types have a medullary layer. This is followed by the cortex, which is the thickest layer and consists of compressed, keratinized cells that determine the texture of the hair (straight, curly). The outermost layer is the cuticle, which consists of very hard, keratinized cells that serve as a protective layer. Hair growth starts at the hair bulb within the skin, where basal cells produce keratinocytes that eventually become part of the hair shaft as they are pushed up through the follicle. As it grows, the hair shaft, made of these three layers, is entirely composed of dead, keratinized cells and hence, has no sensation.