One of the differences between involuntary and voluntary muscles is how each muscle moves. An involuntary muscle is one that can't be controlled. A voluntary muscle, however, is one that can be controlled through stimuli, such as movement.
Involuntary and voluntary muscles also appear differently when viewed under a microscope. Involuntary muscle, called smooth muscle, is located within blood vessels, digestive system and internal organs, with the exception of the heart. It looks smooth when viewed under a microscope and doesn't have the striations or stripes that are seen in voluntary muscle tissue.
Voluntary muscles are also called skeletal muscles. These are the muscles attached to the bones, and movement is caused through contraction of these muscles. Every movement a body makes is due to voluntary muscles contracting and relaxing. There are several proteins contained in voluntary muscles that help the muscles to contract and relax, but the two primary proteins are myosin and actin. These muscles contain more than one nucleus and, depending upon the part of the body, can be up to 30 centimeters in length.
A third type of muscle, called cardiac muscle, is found within the body. This muscle is only found within the heart. It is a type of involuntary muscle, meaning it is one that can't be controlled.