The Muscular System
Did you know that muscles churn the food in your stomach, deform your lungs so they fill with air, and change the diameter of your veins and arteries to adjust your blood flow? Even when you are not thinking about them, muscles are hard at work to keep things in your body moving. Your muscular system also gives you the ability to talk, smile, eat, walk, swim and play. Every motion in your body, every movement that you make relies on muscle.
Skeletal muscles cannot accomplish their tasks alone: they need an anchor point―a bone―on which they can exert their action. The associated force is the result of the muscle shortening and stretching that comes from microscopic, caterpillar-like motors sliding past each other at an incredible speed. In the blink of an eye, your muscular system gives you the ability to get up and go!