Anatomy, Physiology, and Histology of Hair and Skin
What this domain tests
Anatomy, physiology, and histology items test the structure of skin and hair, the growth cycle, and the bones, muscles, and nerves of the head and face that affect barbering services.
Skin and hair histology
Skin has three layers: epidermis (stratum corneum, lucidum, granulosum, spinosum, basale), dermis (nerves, glands, follicles, blood vessels), and subcutaneous tissue. The hair follicle is a tube in the dermis; its base is the bulb, which fits over the papilla, the blood supply that feeds growth. Sebaceous glands attach to the follicle and secrete sebum; the arrector pili muscle contracts in cold or emotion.
Hair has three layers: cuticle (protective scales), cortex (bulk, pigment, bonds), and medulla (central core, often absent in fine hair). Growth cycles: anagen (active growth, years), catagen (transition, weeks), telogen (resting, months, then shedding).
Bones, muscles, nerves
Bones: frontal, parietal, temporal, occipital, zygomatic, maxilla, mandible. Muscles: frontalis, temporalis, occipitalis, masseter, platysma, orbicularis oculi and oris, mentalis, procerus, corrugator. Nerves: trigeminal (fifth cranial) supplies sensation to the face; facial (seventh cranial) supplies the muscles of expression.
Worked example
A client reports numbness and tingling across the cheek after a service. Reasoning: sensation is carried by the trigeminal nerve; persistent numbness is not a normal barbering outcome. Stop, document, and refer to a physician rather than massaging the area.
Traps
- Saying hair grows from the papilla rather than the bulb.
- Confusing anagen with telogen when explaining shedding.
- Mixing up the fifth and seventh cranial nerves.
- Calling the medulla the pigment layer; pigment is in the cortex.