The muscular system biology lesson for kids: 1st, 2nd, 3rd, 4th, 5th, 6th and 7th grades biology lesson.
Human beings move around. The way we do this is by the work of muscles. Muscles make up about half of our body weight, and allow us to move because they are anchored to our bones. There are also muscles in the heart and, blood vessels, which move blood around the body, and in the digestive tract, for moving the food we eat from our mouths down to our anuses. Every muscle essentially does one thing: contact, meaning it get smaller. When it relaxes, it goes back to its normal, looser state.
Skeletal muscles are usually the biggest muscles of the body, and are the only voluntary muscles, meaning that they are the only muscles that we can consciously control. Every one of these muscles has nerves that tell them how and when to move, as well tendons, bands of connective tissue that attaches the muscles to the bones. These muscles allow us to move by pulling two bones together. We can pull our bones two limbs many both forward and back because our muscles work opposite each other.
Then, there are visceral muscles. These are the muscles in the blood vessels, as well as the stomach and intestines. These are “smooth” muscles, because of how they look under a microscope. These muscles work together to perform peristalsis, a wave-like motion in the esophagus (the tube that leads from the mouth to the stomach), stomach, and intestines that push the digesting food along.
Have you ever tried to control your stomach or your blood vessels by thinking about it? You can’t, because visceral muscles are involuntary, and our conscious mind has no control over them. The only exception to this is the diaphragm, a smooth muscle that can be controlled consciously for a while. That’s how we’re able to hold our breaths under water when we’re swimming.
The last kind of muscles are cardiac muscles, the muscles that exist in the heart. These muscles are very important because they have to give our blood a big push that helps it move around the entire body. Cardiac muscles are also involuntary, which is good because our heart needs to keep beating even while we’re asleep. These muscles are special because they are self-stimulating, and so they’re able to keep a steady rhythm even without nerves. The nervous system can tell them to speed up and slow down, though.
So, all these different kinds of muscles have very important functions in our bodies. We wouldn’t be able to so anything without them!