The melanin is replaced by air bubbles in the hair shaft. Hair follicles are normally at a slight angle in the skin. The arrector pili muscles are regulated by the nervous system and are activated by cold external temperatures or fright. They detect if a hair shaft is moved. A NAIL consists of a plate of hard, keratinized epidermal cells that form a clear protective covering on the dorsal surface of the distal part of a finger or toe.
Nails protect the ends of the digits from trauma.
Our fingernails help us to grasp and manipulate small objects. The nail body appears pink because of the rich bed of capillaries in the underlying dermis. The nail matrix contains rapidly dividing epithelial cells. As the nail cells are produced by the matrix, they become heavily keratinized, and the nail body slides distally over the nail bed. The average growth rate of fingernails is 1 mm per week, but the growth rate is somewhat slower in toenails.