Life without muscles would not be possible. Heartbeat, blood circulation, digestion, elimination, sweating, breathing, chewing, vision, movement etc are all controlled by various types of muscle. Basically there are three types of muscle:

  1. Skeletal muscles, the voluntary muscles connected to the skeletal system
  2. Smooth muscles or involuntary muscles like the muscles of bladder, gut, blood vessels etc, and
  3. Cardiac or heart muscles.

The skeletal muscles are very complex in their structure. The smallest units of muscles consist of thin and thick filaments made up of protein chains, actin and myosin respectively. These filaments cluster together in the sarcomere (sarcos - flesh, mere - part). These sarcomeres bundle together to form myofibril (myos - muscles, fibrillae - small fibres) which in turn form muscle fibre. A group of muscle fibres form muscle fascicle, which are units of skeletal muscles. So the progression is: protein chains - filaments -sarcomeres - myofibril - muscle fibres - fascicle - units of skeletal muscles.