Skin and Hand/Arm Anatomy
Skin layers and functions
The epidermis is the outer, avascular layer; its basal layer holds melanocytes and its surface is the stratum corneum of dead keratin cells. The dermis carries collagen, elastin, nerves, glands, and blood vessels. The subcutaneous layer stores fat and cushions. Skin protects, senses, regulates temperature, excretes and secretes, and absorbs limited substances - which is why chemical contact matters. Nails are appendages of the skin, so skin health is nail health.
Bones and joints
Each hand has 8 carpals, 5 metacarpals, and 14 phalanges. The forearm pairs the radius (thumb side) with the ulna (pinky side); the humerus is above. Joints include the wrist, metacarpophalangeal knuckles, and the interphalangeal joints of each digit.
Muscles, nerves, vessels
Flexors bend the fingers, extensors straighten them. The median, ulnar, and radial nerves supply sensation and movement; the ulnar nerve serves the little-finger side, the median nerve the thumb and middle fingers. The radial and ulnar arteries feed the hand, and lymph vessels and nodes drain it.
Traps
Mixing up radius and ulna; saying the nail plate has nerve endings (it does not - the nail bed does); treating massage as risk-free for a client with a circulatory problem; and forgetting that the eponychium and hyponychium are living tissue that seal out infection.
Rule of thumb
Trace your own arm: thumb side is radial, pinky side is ulnar. That one landmark answers most of the nerve, vessel, and bone questions on this exam.