Basics of the Muscular System

Lesson Plan - Get It!

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Your body has a complex muscle system that functions to help you grow and move.

There are over 600 muscles in your body, each with a specific job! Some muscles are involuntary, meaning that they operate without instructions from the brain, while others are voluntary, and must be instructed to move.

Before you continue, if you missed or would like to review the first Related Lesson in our Muscular-Skeletal System series on the skeletal system, you can find it in the right-hand sidebar.

• Do you tell your heart to beat?

The heart is a great example of an involuntary muscle because it contracts without any direct instructions!

No matter what job the muscle has, every muscle is made up of tiny fibers bundled densely together. These cells contract and release as needed by the body.

The job of the muscle depends on the type of muscle. There are three types: smooth, cardiac, and skeletal muscles.

• Smooth muscles have a smooth appearance because they are made of sheets or layers. Smooth muscle is involuntary, meaning that you cannot control it. Examples of smooth muscle include the esophagus, that passes food from the mouth to the stomach. It contracts to move food down without direction from the brain. The muscles along your digestive tract contract and release to move the food through the intestines where nutrients are taken in by the body. Smooth muscles are found throughout your body, helping you function daily!

• Cardiac muscle is only found in the heart and is involuntary! It is a very special type of muscle that helps the heart pump blood to the entire body. It is similar to skeletal muscle, but has a structure that allows the cells to contract in a wave-like pattern so the muscle acts as a pump for blood.

• The last type of muscle is skeletal muscle or striated muscle. This type of muscle is voluntary, and it helps us move. These are the muscles we use to run, jump, and kick a soccer ball. Skeletal muscles work with your skeletal system to allow growth and movement. They are attached to bones by tendons. Tendons are dense, tough tissue that provides an attachment between bones and muscles. Notice how the biceps tendon attaches the bicep muscle to the radius bone? This connection allows the arm to bend and stretch.

All of these muscles work together to help you breathe, digest food, and enjoy time outdoors. Without involuntary muscles, you would have to control life processes like pumping blood or swallowing food. Voluntary muscles help us walk, lift babies, and swim. Both types are needed in order to grow and develop!

Discuss what you have learned about muscle types with a parent or teacher before moving on to the Got It? section, where you will explore more about muscle groups in the body.