Final answer:
Hair with a hard cuticle is strong and protected due to its outer layer of overlapping cells. Hair growth involves dead, keratin-filled cells, known as keratinocytes, forming the hair shaft. The entire visible part of the hair is composed of keratin, a non-sensory material that allows for pain-free cutting or shaving.
Step-by-step explanation:
Hair with a hard, closed, or compact cuticle layer is indicative of hair that has a strong outermost layer, which gives it resilience against external factors. The cuticle in hair consists of overlapping cells that resemble roof shingles, providing a protective layer to the hair underneath. Hair is a keratinous filament that grows from a hair follicle located within the dermis of the skin. The filament is mainly composed of dead, keratin-filled cells known as keratinocytes. The human body is covered with hair follicles, which serve multiple functions such as sensory input, filtering, and regulating body temperature.
The structure of a hair strand is intricate, with a medulla forming the core, surrounded by the cortex and then the cuticle. The hair matrix at the base of the hair follicle produces new keratinocytes, which get pushed up to form the hair shaft as the hair grows. The entire hair that is visible outside the skin is composed of this protein, rendering it non-sensory and allowing actions such as cutting or shaving without pain since the hair is already dead.