Final answer:
The medulla is the central core of hair, often termed the pith, and does not contribute to chemical texture services. It is surrounded by the cortex, responsible for hair texture, and the cuticle, which is the outermost protective layer.
Step-by-step explanation:
The medulla is often called the pith or core of the hair and does not play a role in chemical texture services. The medulla forms the central core of the hair and is surrounded by the cortex, which is the second or middle layer of the hair. The cortex itself is enveloped by an outer layer called the cuticle. The cuticle is the outermost layer of keratinocytes originating from the hair matrix.
Hair growth and its structural integrity start from the hair bulb, where basal cells produce keratinocytes. These cells get keratinized and form the hair shaft as they are pushed through the follicle to the surface. The cortex determines hair texture, such as being straight or curly, which is influenced by the shape of the hair follicle. While the medulla, when present, may contribute to the hair's structure, it does not affect chemical texturing processes which involve the cuticle and cortex layers of the hair.