|MadSci Network: Anatomy|
Dear Sarah, Interesting question. There are 26 bones, including 7 in the wrist and 19 in the fingers and thumb (four for each finger and three for the thumb) in a normal adult hand. In children, it takes until about age 6 or 7 for all the wrist bones to fully form and become hardened. The number of tendons and muscles is higher, but also much harder to put exact numbers on. Your wrist is chock full of muscles and tendons that control the hand and fingers, and there are many that are in the hand, plus some that are partly in both. For every finger and the thumb, there are at least three pairs of what are called “flexors” (or “abductors”) and “extensors,” i.e., muscles with tendons connected to them that curl (flexors) or open (extensors) the fingers and thumb. Some bend the digit at the first knuckle, as when you point at something and move your index finger up or down, and some curl the rest of the finger or thumb, as when you make a fist. Then there are muscles that move the fingers sideways, as when you spread your hand. Many of the muscles and tendons split at either end and connect to two different fingers, and there may be more than one name for different parts. All together, 4 fingers plus one thumb is 5, times at least 3 motions is 15, times 2 directions is 30, plus quite a few others that are involved in things like cupping the hand or compressing the palm when you move the thumb toward the little finger. The muscles for the sideways motions and for compressing the palm are in the hand itself, and all the tendons are at least partly within the hand. Roughly speaking, there are about 40 tendons and 20 muscles within the hand, and another 20 muscles in the wrist that connect to the hand and fingers through tendons. I hope this answers your question. Paul Odgren, Ph.D. Department of Cell Biology University of Massachusetts Medical School, Worcester
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