3.42 Muscle Facts

Did you know your heart is a muscle? Learn about the different types of muscles in your body, how muscles work, and what muscles are made of in this lesson.

Mighty Muscles

Did you know your heart is a muscle? That’s right, your heart is one of the over 600 different muscles in your body. Humans have so many muscles that they make up half of our body weight.

The main job of all muscles is to help parts of your body move. Some of your muscles work on their own while others count on you to tell them what to do.

Fibers and More Fibers

Your muscles are made of thousands of tiny, stretchy fibers that are like thin elastic strings. Many bundles of fibers are found in each muscle. The bigger a muscle, the more fibers it has and the stronger it is.

Muscles are made of bundles of tiny, stretchy fibers.
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1. Main points:

The heart is one of over 600 muscles in the human body, which collectively make up half of our body weight. Muscles, essential for movement, consist of thousands of tiny, stretchy fibers, with larger muscles containing more fibers and being stronger.

2. Questions:

• Content Analysis: What is the primary function of muscles in the human body?
• Contextual Analysis: How does the structure of muscles with fibers contribute to their strength and function?
• Linguistic Analysis: What words in the text describe the characteristics of muscle fibers?

3. Further Discussion:

Why is it important for some muscles to work automatically, while others require our control?

4. Answers:

• Content Analysis: "The main job of all muscles is to help parts of your body move."
• Contextual Analysis: "The bigger a muscle, the more fibers it has and the stronger it is."
• Linguistic Analysis: Words like "tiny," "stretchy," "fibers," and "elastic strings" describe the characteristics of muscle fibers.

How Muscles Work

Muscles move your body by contracting and relaxing. When a muscle contracts, its fibers move closer together causing the whole muscle to shorten. When a muscle relaxes, the fibers move back to their original spots, and the muscle returns to its normal size.

When a muscle contracts, its fibers move closer together, and the muscle gets shorter.

Since muscles can only pull when they contract and not push, muscles usually work in teams to help you move. When one muscle contracts – or pulls – its teammate relaxes.

Think about picking up a glass of water to take a drink. When you flex your arm to bring the glass close to your mouth, your biceps – the muscles on the top of your arm – contract, while your triceps – the muscles on the back of your arm – relax. When you’re done drinking, your triceps contract and your biceps relax, so you can straighten your arm and put your glass back down. Your biceps and triceps are an arm-moving team!

Muscles work in teams to move your body by contracting and relaxing.

Three Types of Muscles

Humans have three different types of muscles: cardiac, smooth and skeletal.

Skeletal Muscles

Skeletal muscles are called ‘skeletal’, like skeleton, because they move your bones. Skeletal muscles are voluntary muscles – you tell them what to do. When you want to raise your hand in class, your brain sends a message to the skeletal muscles attached to the bones in your arm to lift your arm high.

Smooth Muscle

Just like skeletal muscles help your bones move, smooth muscles help your organs move. Smooth muscles are involuntary muscles – they work without you having to think about it. You have smooth muscles all over your body to help you function.

What was the last thing you ate? Did you have to think about digesting your food? Once you finish eating, you don’t have to think about digestion because the smooth muscle in your stomach gets to work by itself.

Cardiac Muscle

Cardiac muscle is the very thick muscle that makes up your heart. Cardiac muscle works like a pump pushing blood out of your heart to the rest of your body. Just like smooth muscle, cardiac muscle works without you having to think about it.

1. Main points:

Muscles move by contracting and relaxing, often working in pairs. There are three types of muscles in humans: skeletal (voluntary, moving bones), smooth (involuntary, moving organs), and cardiac (involuntary, pumping blood).

2. Questions:

• Content Analysis: How do muscles function to move the body?
• Contextual Analysis: What are the differences between skeletal, smooth, and cardiac muscles?
• Linguistic Analysis: What words in the text describe the action of muscles contracting and relaxing?

3. Further Discussion:

Why is it important for some muscles to be under voluntary control while others work involuntarily?

4. Answers:

• Content Analysis: "Muscles move your body by contracting and relaxing… When one muscle contracts… its teammate relaxes."
• Contextual Analysis: "Skeletal muscles are voluntary muscles… Smooth muscles are involuntary muscles… Cardiac muscle works like a pump pushing blood out of your heart."
• Linguistic Analysis: Words like "contracting," "relaxing," "shorten," and "pulls" describe the action of muscles.

Lesson Summary

There are over 600 different muscles in your body that are made of many tiny, stretchy fibers. Moving your body is the main job of your muscles. Muscles move by contracting and relaxing. There are three different types of muscles: skeletal muscle, smooth muscle and cardiac muscle. Involuntary muscles move on their own, while voluntary muscles take orders from you.