How many bones are in the human hand?
The human hand has 27 bones, not counting the variable sesamoid bones. These include 14 phalanges in the fingers and thumb, five metacarpals, and eight carpal bones in the wrist.
Questions about Hand
Short answers, pulled from the story.
What makes a hand different from a paw or claw?
A true grasping hand requires an opposable thumb, the ability to bring the thumb opposite the fingers in a motion called opposition. Paws, claws, and talons are grasping appendages but are not scientifically considered hands, and only the primate order has true grasping hands.
Why is the palm of the hand lighter than the back?
Genes expressed in the dermis of palmoplantar skin inhibit melanin production and the ability to tan, so the palm runs lighter than the back of the hand, an effect strongest in dark-skinned individuals. These same genes thicken the stratum lucidum and stratum corneum of the epidermis.
Which nerves control the human hand?
The hand is innervated by the radial, median, and ulnar nerves. The radial nerve supplies the finger extensors and thumb abductor, the median nerve supplies most flexors and the thumb opponens, and the ulnar nerve supplies the remaining intrinsic muscles.
How did the human hand evolve?
The hand evolved from the pectoral fin, since the precursors of its intrinsic muscles are present in the earliest fishes, making it older than the arm. Primate hands developed from the mobile hands of semi-arboreal tree shrews, and human dexterity arose largely from direct monosynaptic connections between the brain's motor cortex and the spinal motoneurons of the hand muscles.
What are common injuries and disorders of the hand?
Common fractures include the scaphoid fracture, the Boxer's fracture of a metacarpal neck, and thumb-base breaks such as Rolando and Bennet's fractures. Disorders include carpal tunnel syndrome, Dupuytren's contracture, rheumatoid arthritis, and genetic conditions like polydactyly, syndactyly, ectrodactyly, and amelia.