<img src="https://d5nxst8fruw4z.cloudfront.net/atrk.gif?account=iA1Pi1a8Dy00ym" style="display:none" height="1" width="1" alt="" />
Skip Navigation

13.12: Skeletal Muscles

Difficulty Level: At Grade Created by: CK-12
Atoms Practice
Estimated7 minsto complete
Practice Skeletal Muscles
This indicates how strong in your memory this concept is
Estimated7 minsto complete
Estimated7 minsto complete
Practice Now
This indicates how strong in your memory this concept is
Turn In

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.



Structure of a skeletal muscle

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

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.



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). 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?


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


  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.

    Notes/Highlights Having trouble? Report an issue.

    Color Highlighted Text Notes
    Please to create your own Highlights / Notes
    Show More


    muscle fiber

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


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

    Image Attributions

    Show Hide Details
    Difficulty Level:
    At Grade
    Date Created:
    Feb 24, 2012
    Last Modified:
    Aug 28, 2016
    Save or share your relevant files like activites, homework and worksheet.
    To add resources, you must be the owner of the Modality. Click Customize to make your own copy.
    Please wait...
    Please wait...
    Image Detail
    Sizes: Medium | Original
    Add Note
    Please to create your own Highlights / Notes