Did you know you have more than 600 muscles in your body? They help you do almost everything — from pumping blood throughout your body to lifting your heavy backpack. You control some of your muscles and others, like your heart, do their jobs without you thinking about them at all.
muscle joints animatedMuscles are all made of the same material, a type of elastic tissue (sort of like the material in a rubber band). Thousands, or even tens of thousands, of small fibers make up each muscle. You have three different types of muscles in your body: smooth muscle, cardiac (say: kar-dee-ak) muscle, and skeletal (say: skel-uh-tul) muscle.
Smooth Muscles
Smooth muscles are sometimes also called involuntary muscles and they are usually in sheets, or layers, with one layer of muscle behind the other. You can't control this type of muscle. Your brain and body tell these muscles what to do without you even thinking about it. You can't use your smooth muscles to make a muscle in your arm or jump into the air.
But smooth muscles are at work all over your body. In your stomach and digestive system, they contract (tighten up) and relax to allow food to make its journey through the body. Your smooth muscles come in handy if you're sick and you need to throw up. The muscles push the food back out of the stomach so it comes up through the esophagus (say: ih-sah-fuh-gus) and out of the mouth.
Smooth muscles are also found in your bladder. When they're relaxed, they allow you to hold in urine (pee) until you can get to the bathroom. Then they contract so that you can push the urine out. These muscles are also in a woman's uterus, which is where a baby develops. There they help to push the baby out of the mother's body when it's time to be born.
You'll find smooth muscles at work behind the scenes in your eyes, too. These muscles keep the eyes focused.
source: http://kidshealth.org
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