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Skeletal Muscles

Skeletal muscles are comprised bundles of muscle fibers. Muscles can only contract and must work in pairs.

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Skeletal Muscles

How do your bones move?

By the contraction and extension of your skeletal muscles. Notice how the muscles are attached to the bones. The muscles pull on the bones, causing movement.

Skeletal Muscles

There are well over 600 skeletal muscles in the human body, some of which are identified in Figure below. Skeletal muscles vary considerably in size, from tiny muscles inside the middle ear to very large muscles in the upper leg.

Skeletal muscles in the body

Skeletal Muscles. Skeletal muscles enable the body to move.

Structure of Skeletal Muscles

Each skeletal muscle consists of hundreds or even thousands of skeletal muscle fibers. The fibers are bundled together and wrapped in connective tissue, as shown Figure below. The connective tissue supports and protects the delicate muscle cells and allows them to withstand the forces of contraction. It also provides pathways for nerves and blood vessels to reach the muscles. Skeletal muscles work hard to move body parts. They need a rich blood supply to provide them with nutrients and oxygen and to carry away their wastes.

You can watch a video about skeletal muscle structure and how skeletal muscles work below.

 

 

Structure of a skeletal muscle

Skeletal Muscle Structure. A skeletal muscle contains bundles of muscle fibers inside a “coat” of connective tissue.

A description of the anatomy of muscle cells is shown below: 

 

Skeletal Muscles and Bones

Skeletal muscles are attached to the skeleton by tough connective tissues called tendons (see Figure above). Many skeletal muscles are attached to the ends of bones that meet at a joint. The muscles span the joint and connect the bones. When the muscles contract, they pull on the bones, causing them to move.

You can watch a video showing how muscles and bones move together below: 

 

  

Muscles can only contract. They cannot actively extend, or lengthen. Therefore, to move bones in opposite directions, pairs of muscles must work in opposition. For example, the biceps and triceps muscles of the upper arm work in opposition to bend and extend the arm at the elbow (see Figure below).

You can watch an animation of these two muscles working in opposition in the video below. What other body movements do you think require opposing muscle pairs? 

 

 

 

Opposing muscles example

Triceps and biceps muscles in the upper arm are opposing muscles.

Use It or Lose It

In exercises such as weight lifting, skeletal muscle contracts against a resisting force (see Figure below). Using skeletal muscle in this way increases its size and strength. In exercises such as running, the cardiac muscle contracts faster and the heart pumps more blood. Using cardiac muscle in this way increases its strength and efficiency. Continued exercise is necessary to maintain bigger, stronger muscles. If you don’t use a muscle, it will get smaller and weaker—so use it or lose it.

Exercising individual

This exercise pits human muscles against a force. What force is it?

Summary

  • Skeletal muscles are attached to the skeleton and cause bones to move when they contract.

Explore More

Use this resource to answer the questions that follow.

  1. What body system controls the skeletal muscles?
  2. Define the epimysium and the fascia.
  3. What makes up a skeletal muscle organ?
  4. What is a tendon or an aponeurosis?
  5. What are the A-band and I-band?

Review

  1. What is a muscle fiber?
  2. What is the function of skeletal muscle?
  3. How are skeletal muscles attached to bones?
  4. Explain why many skeletal muscles must work in opposing pairs.

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    Vocabulary

    muscle fiber

    Long, thin muscle cell that has the ability to contract, or shorten.

    tendon

    Tough connective tissue that attaches skeletal muscle to bones of the skeleton.

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