Muscular

The **__Muscular System__** is made up of Muscles. There are three different kinds: __Cardiac Muscle__ Skeletal Muscles are voluntary muscles. They help you run and jump ect. Ex. The muscles on your arms and legs Cardiac Muscles are the muscles that make up your heart (invonuntary) Ex. The Heart Smooth Muscles make up involuntary organs that are usually hollow Ex. Stomach, Intestines, and the Blatter
 * Skeletal Muscles
 * Cardiac Muscles
 * Smooth Muscles

Muscles always work in pairs. They do this in order to bend or extend your arm. When one muscle contracts (tighten) the muscle opposite it has to expand (spread apart). Ex. If your arm is fully extended and you want to bend it again the muscle on the inner part of your arm will contract and then the muscle on the outer part of your arm will have to expand to let the opposite muscle bend your arm or else your arm will never be able to move.
 * Why Do Muscles Work In Pairs?**