What are muscles?
Muscles are an organ, composed of muscle tissue that contracts to produce a particular movement. Muscles are grouped in different ways.
If they are voluntary , that is we have to think about them, to make them move. Or if they are not, they are involuntary . Lastly, there is cardiac muscle.
As a whole, they make up about 36% of the body. The muscles that you move by thinking are also called skeletal muscles since the use bones as levers. These are all most always in pairs.
The involuntary muscles are found in all hollow organs except for the heart. They move very slowing in a way called peristalsis. These muscles are also called smooth muscles.
Cardiac (heart) muscles pump the heart.