Where do mitotic cells begin their growth in relation to hair?

Mitotic cells responsible for hair growth originate in the hair matrix, which is located at the base of the hair follicle. This area is crucial for producing new hair cells through the process of mitosis. As these cells divide and grow, they push older cells upwards, eventually forming the hair shaft that extends beyond the scalp.

The hair matrix is rich in keratinocytes, which are the primary cells that contribute to hair structure. As these cells multiply, they keratinize, leading to the formation of the hair fiber itself. This biological process is essential for the growth and renewal of hair, making the hair matrix the true starting point for mitotic activity in relation to hair growth.

In contrast, while the dermis provides support and nourishment to hair follicles and contains important structures such as blood vessels and nerves, it does not directly initiate hair growth. The follicle opening and the scalp surface are also involved in the overall health and appearance of hair but are not the sites where mitotic activity occurs. Therefore, the hair matrix is the correct answer, as it is the specific region where hair cells undergo division and differentiation.