Anatomy, Physiology, Chemistry, and Electricity
Anatomy Essentials
Cells form tissues, tissues form organs, organs form systems. Know the bones of the skull and face, and the muscles you touch: frontalis (forehead), temporalis, masseter (chewing), orbicularis oculi (eye closure), mentalis, and platysma. Nerves: the fifth cranial (trigeminal) is the chief sensory nerve of the face, and the seventh cranial (facial) is the chief motor nerve. The circulatory system supplies nutrients and oxygen; the integumentary system is the skin, hair, nails, and glands.
Chemistry Basics
Matter is anything with mass; elements cannot be broken down, atoms are the smallest unit, and compounds combine elements. Physical changes do not create new substances; chemical changes do. The pH scale is logarithmic, so each whole number is a tenfold change. Solutions are evenly mixed; suspensions settle and need shaking; emulsions blend oil and water with an emulsifier. Surfactants let water lift oil - the basis of shampoo. Understand oxidation and reduction, and know that bonds break and re-form in every chemical service.
Electricity and Safety
Direct current (DC) flows one way; alternating current (AC) reverses direction and is what wall outlets supply. Volts measure pressure, amps measure current, ohms measure resistance, and watts measure power. Galvanic current is a constant DC used historically for product penetration; faradic is an interrupted current used for muscle stimulation. Water and electricity never mix - use GFCI outlets, keep cords off wet floors, and never touch a client while they contact a plugged appliance carelessly.
Traps and Rule of Thumb
Questions swap trigeminal and facial nerves, confuse AC and DC, or claim pH 4 is twice as acidic as pH 5. Rule of thumb: one pH step equals ten times the acidity or alkalinity.