Related Sciences (Anatomy, Physiology, Chemistry, Microbiology)
Anatomy and physiology
Know the bones of the skull and face (frontal, parietal, occipital, temporal, zygomatic, mandible, maxilla) and the muscles that create expression and chewing: frontalis, temporalis, masseter, occipitalis, sternocleidomastoid, trapezius. The trigeminal nerve supplies sensation to the face; the facial nerve controls expression. Blood supply includes the superficial temporal, external maxillary (facial), occipital, posterior auricular, and supraorbital arteries. Hair has three layers, the cuticle, cortex, and medulla, and grows in cycles: anagen (growth), catagen (transition), telogen (rest). The arrector pili muscle causes goosebumps; the sebaceous gland lubricates.
Chemistry and microbiology
pH is logarithmic: pH 5 is 100 times more acidic than pH 7. Oxidation adds oxygen or removes hydrogen; reduction does the opposite. Surfactants lift oil and dirt. Microorganisms include bacteria, viruses, fungi, and parasites. Pathogens cause disease; nonpathogens do not. Some bacteria form spores that resist ordinary disinfection. Bloodborne pathogens include hepatitis B and HIV; fungal infections include tinea (ringworm), and pediculosis is a parasite infestation. Disinfection kills most pathogens but not necessarily spores; sterilization does.
Traps
Examiners mix up anagen and telogen, cuticle and cortex, and the trigeminal and facial nerves. They also imply all bacteria are harmful or that a disinfectant sterilizes. Remember that spores are the hardest to kill and that porous implements cannot be disinfected.
Rule of thumb
For any layer, nerve, or cycle question, anchor to function: cuticle protects, cortex gives strength and color, medulla is the core; anagen grows, telogen rests.
Worked example: A client asks why hair sheds in the fall. Many hairs enter telogen together, so shedding increases after the resting phase; this is normal, not a sign of disease.