Final answer:
Monilethrix is the condition where beads or nodes form on the hair shaft, and the hair matrix contains a layer of basal cells responsible for new hair cell growth.
Step-by-step explanation:
The condition in which beads or nodes form on the hair shaft is called monilethrix. This condition often results in fragile hair, breakages, and the appearance of the hair having a beaded or necklace-like pattern. The hair matrix contains a layer of basal cells, which are responsible for the growth of new hair cells and are the most actively dividing. In the context of hair growth and health, other terms are also significant, such as anagen, which is the active phase of the hair growth cycle, and the arrector pili, a muscle that responds to stimuli causing the hair to stand up.