Final answer:
The cuticle is the outermost layer of the hair shaft, consisting of overlapping keratin-filled keratinocytes. These cells originate from the hair matrix and form a protective layer as they die and become filled with keratin, giving the hair its strength and structure.
Step-by-step explanation:
The cuticle in hair is the outermost layer of the hair shaft and is made up of flat, scale-like cells, known as keratinocytes, that overlap each other like shingles on a roof. This layer originates from the hair matrix, located at the base of the hair follicle, where basal cells divide and differentiate to form the various layers of the hair. The hair shaft itself is composed of these dead keratinocytes that are filled with keratin, which is a tough and fibrous protein, giving hair its structure and strength.
The hair follicle structure includes the internal root sheath, which surrounds the hair root and ends at the hair shaft, and the external root sheath, an extension of the epidermis that contains basal cells which become more keratinous as they move upwards. The entire hair follicle is anchored to the dermis by the glassy membrane. As new cells are produced by the hair matrix, the hair shaft is pushed upwards, through the follicle, eventually emerging above the skin's surface. Because the cells are filled with keratin and die as they move away from the matrix, the visible part of the hair is considered dead tissue, which is why we do not feel any sensation when it is cut or styled.