Final answer:
The medulla is the innermost layer of hair, surrounded by the cortex and the cuticle as the outermost layer, and contributes to hair texture.
Step-by-step explanation:
The innermost layer of hair is composed of the medulla, which forms the central core of the hair. This is surrounded by the cortex, a layer of compressed, keratinized cells, and then by the outermost layer known as the cuticle. Not all hair types have a medullary layer, but when present, it contributes, along with the cortex, to the hair texture like straightness or curliness. These characteristics are determined by the shape and structure of the cortex and the medulla, as well as the shape of the hair follicle itself. The hair shaft that we see is completely void of sensation because it is composed entirely of dead keratinized cells.