All muscles are not created equal. In fact, your body has three very different types of muscle, each of which does a different kind of work:
• Skeletal. These are the muscles most people think of first. They’re anchored to your bones and under your conscious control. You use these muscles to move your body parts (and to impress potential dates at the gym).
• Smooth. Most of these muscles are deeper inside your body, in thin sheets that line internal passages like your digestive tract, your blood vessels, your bladder, and (if you ve got one) your uterus. You also find smooth muscles closer to the surface, where they can make the several million fine hairs on your body stand on end.
• Cardiac. You find this muscle type in just one place—your heart. Like smooth muscle, cardiac muscle is beyond conscious control, meaning you can’t will it to contract or stop contracting. However, the structure of cardiac muscle is more similar to skeletal muscle than to smooth muscle, and its uncanny sense of rhythm is something no other muscle can match.
Source of Information : Oreilly - Your Body Missing Manual