Перевидите текст Smooth muscles — sometimes also called involuntary muscles — 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 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 and out of the mouth.
Smooth muscles are also found in your bladder. When they're relaxed, they allow you to hold in urine 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.