Skeletal muscles

 

 

The skeleton

The skeleton is made up of more than 200 bones. It has four main functions:

 

• allows movement.
• gives support.
• provides protection for vital organs.
• to make blood cells

 

 

Joints

Joints are where bones move in different directions, like elbows and knees. Muscles pull bones at joints, but they are not directly connected. Bones have ligaments, which are strong cords that attach them to each other. Muscles have tendons, which are also strong cords that attach them to bones. Muscles contract and relax to move bones at joints.

 

Muscles

Muscles are bundles of cells that form muscle tissue. There are three kinds of muscle cells: cardiac, smooth, and skeletal. Cardiac cells pump blood in our bodies. Smooth cells make thin muscles, like in the stomach. Skeletal cells join bones and move them at joints. Muscles can only contract and relax. Skeletal muscles can only pull bones, not push them. So they work in pairs, called antagonistic muscles, to move joints back and forth.

 

Antagonistic pairs

Muscles work together in pairs at a joint to allow movement, called antagonistic pairs. One muscle in the pair contracts while the other relaxes. For example, at the elbow joint:

 

• To bend the arm, the bicep contracts and shortens while the tricep relaxes and extends.
• To straighten the arm, the tricep contracts and shortens while the biceps relaxes and extends.

 

 

💪 Knowledge Check: Muscles & Bones

Test your understanding of how the human body moves and supports itself.

1. Which part of the bone is responsible for making red and white blood cells?

• Hard outer bone
• Bone marrow
• Cartilage

2. Muscles can only perform which of the following actions?

• Pushing only
• Pulling only
• Both pushing and pulling

3. When you bend your arm at the elbow, what are the biceps and triceps doing?

• Biceps contract and triceps relax
• Biceps relax and triceps contract
• Both muscles contract at the same time

4. Which tissue connects a muscle to a bone?

• Ligament
• Tendon
• Nerve

Check Your Answers

1. Bone marrow (The "factory" for blood cells).
2. Pulling only (This is why they must work in antagonistic pairs).
3. Biceps contract and triceps relax (The biceps is the agonist in this movement).
4. Tendon (Remember: Tendons for Tightening/moving; Ligaments for Linking bones).

 

Summary:

 

• Muscles can only contract and relax.
• Skeletal muscle is joined to bones, its cells contract to make bones move and joints bend.