Scientific Concepts: Anatomy, Physiology, and Chemistry
Anatomy and physiology
Cells make tissues, tissues make organs, organs make systems. In the skull, know the frontal, parietal, temporal, occipital, zygomatic, maxillary, and mandibular bones. For muscles, origin is the fixed attachment and insertion is the movable one. The frontalis raises the brow, the occipitalis pulls the scalp back, the temporalis and masseter are chewing muscles (masseter at the angle of the jaw), and the platysma tenses the neck. The facial (VII) nerve controls expression; the trigeminal (V) supplies sensation. Arteries you locate by pulse: temporal (above the ear), facial (along the jaw), occipital (base of the skull), and the common carotid. Never massage over swollen lymph nodes.
Chemistry
Matter has mass; elements cannot be broken down further; compounds are chemically joined elements; mixtures are physical - solutions are uniform, suspensions settle, emulsions require an emulsifier. The pH scale is logarithmic from 0 to 14: below 7 acidic, above alkaline, water neutral at 7. Hair and skin sit near 4.5 to 5.5. Oxidation loses electrons (lighteners, permanent color); reduction gains them (thioglycolate). Surfactants clean, emollients lubricate, humectants attract and hold water, preservatives prevent microbial growth.
Traps
Origin and insertion reversed; masseter labeled an expression muscle; pH treated as linear - pH 4 is ten times more acidic than pH 5, not one step.
Worked example: moving a solution from pH 5 to pH 3 makes it 100 times more acidic, because each unit is a factor of ten.