4 Throwing and catching a ball is a good way to work the muscles in your hands arms and shoulders MUSCLES WORK AROUND THE CLOCK Muscles are an important part of your body Anything you can imagine yourself doing uses muscles You need muscles to run throw a ball or ride a bike You also use muscles at times when it seems like you are not doing anything It takes muscles to smile read a book or swallow food Even when you are sleeping many of your muscles
5 are still hard at work Muscles in your digestive system are turning the food you ate for dinner into fuel for your body The muscle in your heart is beating and pumping blood Muscles in your chest are helping you breathe Your muscles work all day and all night too Why don’t all of your muscles sleep when you do Why is this important THINK ABOUT IT When people are asleep they breathe more slowly but many of their muscles are still working hard 5
6 Your body has three types of muscles skeletal muscle cardiac muscle and smooth muscle Skeletal muscle connects to your bones These muscles come in all shapes and sizes because they do different jobs A muscle in your ears is your smallest muscle It moves the smallest bone you have Muscles in your TYPES OF MUSCLES Humans have over 700 muscles but grasshoppers have 900 If people could jump like grasshoppers they could leap across a football field in one bound
legs are large and strong They must move and support your whole body Cardiac muscle is located in the heart It pumps blood by squeezing and relaxing in a regular pattern of beats called the heartbeat Smooth muscle lines the intestines stomach and other organs in the body These muscles are not connected to bones They control what your organs do without you having to think about it How are the muscles in your ears and legs the same How are they different COMPARE AND CONTRAST The heart is a network of highly branched cardiac cells The cells are organized into layers of tissue that are wrapped around the chambers of the heart 7
