1. Chapter 17.2
The Muscular System

2. Movement of the Human Body
All movement is possible because of muscles.
Muscle – an organ that can relax, contract, and provide the force to move your body parts.
You have more than 600 muscles.
Even when you are still you have muscles that are still moving, like your heart beating and your digestive system working.

3. Muscle Control
Voluntary muscles are muscles that you control, like your hand, arm, and leg.
Involuntary muscles are muscles you can’t control, like blood being pumped through blood vessels and food moved through your digestive system.

4. You Body’s Simple Machines - Levers
You muscles and your skeletal system work together.
A lever is a rod that pivots or turns about a point. The point is called a fulcrum. The action of your muscles, bones, and joints are like a lever. Bones are rod, joints are fulcrums, and contraction and relaxation of muscles is the force necessary to move the lever.
Read pg. 492

5. Classification of Muscle Tissue
There are 3 types of muscles: skeletal, smooth, and cardiac.
Skeletal muscles are muscles that move bones. These muscles are stuck to bones by tendons. Skeletal muscles are striated or appear to have stripes. Skeletal muscles are voluntary muscles.
Cardiac muscle is found only in the heart. It is also striated.
Smooth muscles are found in your intestines, bladder, blood vessels, and internal organs. They are nonstriated and involuntary muscles that slowly contract and relax.

6. Working Muscles
Pairs of skeletal muscles work together to allow movement.
When one muscle in the pair contracts the other relaxes (returns to its original length).
Muscles always pull, never push.

7. Changes in Muscles
Over time muscles can become larger or smaller, depending on whether they are used.
Muscles that are exercised regularly respond quickly to stimuli.
When muscles become larger some muscle cells are added but mostly it gets larger because individual muscles cells get larger.
If your muscles are not used they become soft and flabby and lack strength.

8. How Muscles Move
You muscles need energy to contract and relax. Your blood carries energy-rich molecules to your muscle cells – these molecules give energy to muscle cells.
When exercising muscles use energy and the muscle becomes tired and needs rest.