Anatomy, Physiology, and Histology of Hair, Skin, and Nails
This domain tests structure and function: the layers of skin, the anatomy of the follicle, the nail unit, and the bones, muscles, nerves and vessels of the head and face that guide massage and service safety.
Skin
Epidermis is the protective outer layer, with the basal layer producing new cells. Dermis holds collagen and elastin, nerves, glands and blood vessels. Subcutaneous tissue is fat and insulation. Sudoriferous glands (eccrine and apocrine) produce sweat; sebaceous glands secrete sebum into the follicle.
Hair
Each follicle contains a bulb, a papilla supplying blood, and a matrix where cells divide. The shaft has three layers: cuticle (protective scales), cortex (about 90 percent, holding pigment and strength) and medulla (core, sometimes absent). Growth cycles: anagen (active, years), catagen (transition, weeks) and telogen (rest, months, then shedding). Roughly 90 percent of scalp hair is in anagen at any time.
Nails
The nail plate sits on the nail bed, is produced by the matrix, and shows the lunula at its base. Cuticle, eponychium, hyponychium and sidewalls complete the unit. Fingernails grow faster than toenails.
Head, face and neck
Skull bones include frontal, parietal, temporal and occipital; facial bones include mandible, maxilla and zygomatic. Muscles include frontalis, occipitalis, temporalis, masseter (chewing) and platysma. The fifth cranial (trigeminal) nerve carries sensation; the seventh cranial (facial) nerve carries motor control.
Worked example
A client asks whether shaving will make her husband's beard thicker. Reasoning: growth happens at the matrix below the skin surface, so cutting the shaft changes only the visible end, which feels coarser. Rate and density are genetic and hormonal.
Traps that cost marks
Confusing epidermis with dermis, calling the shaft living tissue, and swapping the trigeminal and facial nerves.