The Human Body Guide

, pushing blood through a vast network of vessels to deliver oxygen to every corner of your body. The Command Center:

Working in tandem with the bones is the . With over 600 muscles, this system is responsible for everything from the powerful stride of a sprinter to the microscopic adjustments of the eye. Muscles operate on a simple principle of contraction and relaxation, yet they allow for an infinite range of motion. The Engine: Circulatory and Respiratory Systems The Human Body