The Muscular System

        We have more than 600 muscles in your body. They do everything from pumping blood throughout your body to helping you lift your heavy backpack. You control some of your muscles, while others — like your heart — do their jobs without you thinking about them at all.

          Muscles are all made of the same material, a type of elastic tissue (sort of like the material in a rubber band). Thousands, or even tens of thousands, of small fibers make up each muscle.

         There are three types of muscle:

Skeletal muscle

• There are nearly 650 skeletal muscles in the human body!
• Skeletal muscles are attached to the skeleton
• They work in pairs: one muscle moves the bone in one direction and the other moves it back again
• Skeletal muscles are voluntary muscles - in other words we think about what movements we want to make (at least, usually!) and send messages via our nervous system to tell the appropriate muscle(s) to contract. 
• Muscle contractions can be short, single contractions or longer ones. 

Smooth muscle 

• Smooth muscle is found in our internal organs: in our digestive system, our blood vessels, our bladder, our respiratory organs and, in a female, the uterus. 
• Smooth muscle can stretch and maintain tension over extended periods 
• Smooth muscles are involuntary muscles - in other words we donot have to think about contracting them because they arecontrolled automatically by the nervous system. It would be pretty inconvenient if we had to think about digesting our food, for example!

Cardiac muscle

• As the name should tell you, cardiac muscle is found only in the heart. 
• It can stretch, just like smooth muscle, and contract like skeletal muscle. 
• It is a twitch muscle - it only does short single contractions
• Like smooth muscle, cardiac muscle is involuntary. It'd be rather dangerous if it were voluntary - we could stop our heart beating any time we wanted!