Final answer:
Beads and nodes can form on the hair shaft when there is a disruption in the structure of the hair's cortex, which is the middle layer of keratinocytes in the hair. This can be caused by factors like heat styling or chemical treatments.
Step-by-step explanation:
Beads and nodes can form on the hair shaft when there is a disruption in the structure of the hair's cortex, which is the middle layer of keratinocytes in the hair. The cortex gives hair its strength and shape. The disruption can be caused by various factors, such as chemical treatments, heat styling, or physical damage to the hair.
When the cortex is weakened or damaged, it can result in the formation of beads and nodes along the hair shaft. For example excessive heat from flat irons or curling irons can cause the keratin structure in the cortex to break down leading to the formation of beads and nodes. Similarly chemical treatments like perming or relaxing can alter the protein structure in the cortex resulting in the same effect. In summary beads and nodes form on the hair shaft when there is damage or weakening of the cortex which can occur due to various factors like heat styling or chemical treatments.