Final answer:
The innermost layer of hair, also known as the pith, is referred to as the medulla. This layer of hair is a part of the entire hair structure which also includes the cortex and the cuticle. Hair growth originates from the hair bulb located at the base of the hair follicle.
Step-by-step explanation:
The innermost layer of the hair structure, also known as the pith, is also referred to as the medulla. Hair is a keratinous filament that originates from an epidermal penetration of the dermis, known as the hair follicle. The hair structure has three main parts - the medulla (innermost layer), the cortex (middle layer), and the cuticle (outermost layer). The hair bulb at the base of the follicle is where the production of keratinocytes begins, initiating hair growth. Keratinization is completed as the cells are pushed to the surface, forming the shaft of hair that is externally visible. This external hair is entirely comprised of dead keratinized cells, hence our hair doesn't have sensation.
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