Final answer:
The condition causing beads or nodes on the hair shaft is c) Trichorrhexis nodosa, and the hair matrix includes a layer of basal cells. The hair shaft itself comprises three zones: cuticle, cortex, and medulla.
Step-by-step explanation:
The condition in which beads or nodes form on the hair shaft is called Trichorrhexis nodosa. This condition is characterized by thickening or weak points (nodes) on the hair shaft, which may lead to breakage. The hair matrix contains a layer of basal cells, which are responsible for the production of new hair cells, contributing to hair growth.
A hair shaft is composed of three zones: the outermost zone is known as the cuticle; the middle layer is called the cortex; and the innermost zone is the medulla. Various conditions can affect the hair and scalp, such as alopecia (hair loss), dandruff (flaky scalp), and split ends (when the ends of the hair, usually the oldest and most damaged portion, split).