If you were able to dissect yourself, you’d find that most skeletal muscles attach directly to bone with a tough piece of connective tissue called a tendon. When a muscle contracts, it pulls on the tendon, moving the appropriate bone. Most skeletal muscles stretch over a joint, from one bone to another. A tendon anchors the muscle on both sides. Skeletal muscles aren’t always where you expect them to be—namely, on the body part they control. The muscles that bend your knee, for example, sit inside your thigh. Similarly, the muscles that bend your elbow are inside your upper arm.
One of the more interesting examples of this quirk is found with the muscles that move your fingers, which aren’t anywhere near your 10 digits. If they were, your fingers would be plump, clumsy little sausages. You’d need a jumbo-sized keyboard to type your name and a robot to tie your shoes, and you’d have no chance of playing any instrument requiring more manual dexterity than a plastic whistle.
Instead, the major muscles that move your fingers are in your forearm. To take a look, roll up your sleeve and watch the top of your forearm as you twiddle your fingers around. You’ll see the contractions of the finger-controlling muscles in your arm. Long tendons stretch from these muscles, down your arm and through your wrist, connecting them to your fingers.
When these muscles move, they pull the tendons and jerk your fingers around, somewhat like a puppeteer controlling a marionette. Although your hand does have a few smaller muscles that help precisely position your fingers, the muscles in your forearm hold the real power.
Right now, this fact might seem like little more than a second-rate party trick. But there’s a good reason to understand your tendons—they’re the source of many types of injury. For example, tendons that repeatedly rub against a narrow passage in your body can cause painful inflammation, called tendinitis. Tendinitis commonly involves the tendons around your knees, elbows, shoulders, or wrists.
An even more insidious wrist problem is carpal tunnel syndrome. It occurs when the tendons that control your fingers become chronically swollen and put pressure on your hand’s medial nerve. This happens because both the tendons and this nerve share the narrow passage in your wrist called the carpal tunnel.
Even more catastrophically, you can tear or cut a tendon, which will prevent you from operating the attached body part unless you see a surgeon—fast.
The 50-odd muscles in your face are unique—instead of using tendons, they connect directly to your skin. This attachment gives you remarkable control. It’s the reason your face can communicate the subtlest of emotions, while the skin on your back lacks the same expressive power.
Source of Information : Oreilly - Your Body Missing Manual