1. The Muscular System
                                  

2. 1. The main function of the muscular system is to work with our skeletal system to help us move.

3. How Many?
2. There are about 600 muscles in your body.

4. Involuntary
3. Muscles that are NOT under your conscious control are called involuntary muscles.
Involuntary muscles are responsible for activities such as breathing and digesting food.

5. Voluntary
5. The muscles that are under your control ARE voluntary muscles.
Smiling and turning the pages in a book are actions of voluntary muscles.

6. 6. Three Types of Muscles
Skeletal muscles (striated)
Smooth
Cardiac

7. 6. Skeletal Muscles Voluntary Attach to bones by tendons Work in pairs
As one muscle relaxes, the other contracts
Cells are long and thin
Cells have striped appearance (striated)
React quickly, but tire quickly

8. 7. Smooth Muscles Involuntary
                  
Involuntary
Muscles of internal organs (stomach and intestine)
Cells are smaller and shorter
Cells are arranged in compact layers
React slowly, but do not tire.

9. 8. Cardiac Muscles Found only in the heart
Has characteristics of both skeletal and smooth muscles
Cells are striped and arranged in bundles (skeletal)
Cells are shorter and involuntary
Never tire

10. 9. How do muscles work?
Muscles work by contracting, or becoming shorter and thicker.
Because muscle cells can only contract, not extend, skeletal muscles must work in pairs.
While one muscle contracts, the other muscle in the pair returns to its original length.

11. Muscles in Action
To bend the elbow, the biceps muscle on the front of the upper arm contracts, while the triceps muscle on the back of the upper arm returns to its original length.

12. Muscle Health
                            
Exercise is important for maintaining muscular strength and flexibility.
Exercise makes individual muscle cells grow wider, thicker and stronger.