Anatomy and Physiology of the Hands, Arms, and Nails
Anatomy questions ask whether you can locate and name the structures you touch, explain nail growth, and use anatomy to justify safe technique rather than memorized rules.
The nail unit
- Nail plate: keratinized, with no nerve endings at the visible surface; rests on the nail bed.
- Nail bed: vascular tissue beneath the plate, which is why a healthy plate looks pink and a bruise shows as a dark spot.
- Matrix: the living growth area extending under the proximal nail fold; it produces the plate. Matrix injury causes permanent grooves or distortion.
- Lunula: the visible whitish half-moon - the front edge of the matrix, not the whole matrix.
- Cuticle (eponychium): the non-living seal on the plate. The proximal nail fold is the living skin behind it; you push the fold gently, you do not cut living tissue.
- Hyponychium: the seal under the free edge. Also know lateral folds (sidewalls), nail grooves, and the nail mantle.
- Growth: fingernails advance roughly 3–4 mm per month (about 0.1 mm per day); toenails about 1 mm per month and are thicker. Growth speeds up in summer, in youth, and during pregnancy; it slows with age, poor circulation, illness, and some medications.
Hand and arm structures
Phalanges, metacarpals, and carpals; the DIP, PIP, and MCP joints; flexor and extensor tendons; radial and ulnar arteries feeding the digital arteries; median, ulnar, and radial nerves. This is why a numb fingertip, a cold pale finger, or sudden swelling is a stop-and-refer sign rather than something to file around.
Worked example
A client wants pedicures every two weeks because her fingernails grow quickly. Reasoning from growth rates: fingernail plates advance about 3–4 mm monthly, toenails about 1 mm monthly, and toenails bear load and thicken with age, so regrowth is slower. A four-to-six-week pedicure interval is realistic, while two weeks is usually too soon and invites over-filing of the plate.
Traps that cost marks
Calling the lunula the matrix; describing cuticle work as cutting the cuticle when the target is the proximal fold's non-living seal; treating the plate as living tissue; and assuming ridges or white spots mean a vitamin deficiency.