1. Lesson 4 – The Muscular System

2. Types of Muscles
Involuntary muscles are responsible for such essential activities as breathing and digesting food.
These muscles are under your unconscious control. You do not realize that your body is moving these muscles.
The muscles that are under your conscious control are called your voluntary muscles.
Smiling, turning a page in a book and getting out of your chair are all voluntary muscle movements.

3. Your body has three types of muscle tissue – skeletal, smooth and cardiac muscles/
Some of these muscle tissues are involuntary and some are voluntary.

4. Skeletal Muscles
Skeletal muscles are attached to the bones of your skeleton and provide the force that moves your bones.
A tendon is a strong connective tissue that attaches muscles to bones.
Skeletal muscles are sometimes called striated muscles because the cells in the muscles appear banded or striated.

5. Skeletal Muscles

6. Smooth Muscles
The inside of many internal organs, such as the stomach and blood vessels contain smooth muscles.
Smooth muscles are involuntary muscles.
They work automatically to control certain movements inside your body.
Unlike skeletal muscles, smooth muscle cells are not striated and they react more slowly and tire more slowly.

7. Smooth Muscles

8. Cardiac Muscles
These muscles are found only in your heart. Cardiac muscles have some characteristics in common with both smooth and skeletal muscles. They are involuntary muscles like the smooth muscles and their cells are striated like the skeletal muscles.
Cardiac muscles do not get tired, they can contract repeatedly. Those repeated contractions are known as heartbeats.

9. Cardiac Muscles

10. Muscles at Work
Because muscle cells can only contract, not extend, skeletal muscles must work in pairs.
While one contracts, the other muscle in the pair relaxes to its original length.
Ex: as the biceps contract, the triceps on the back of the upper arm relaxes and returns to its original length.

11. Muscular Strength and Flexibility
When you warm up before exercising, you increase the flexibility of your muscles.
Regular exercise is important for maintaining both muscular strength and flexibility.
A muscle strain or pulled muscle can occur when muscles are overworked or overstretched.
Tendons can also be overworked or overstretched and tear.