Muscle cells are divided into two groups, striated muscle and smooth muscle. Striated muscle cells are characterized by protein arrays that form stripes. Smooth muscles don't have these striations or stripes and appear unmarked when viewed through a microscope.
Muscle cells form muscle tissue, and three types of muscle tissue are found in the human body: smooth muscle, cardiac muscle and skeletal muscle. The movement of smooth muscle is an involuntary process, meaning the muscle contracts and relaxes without conscious thought.
Cardiac muscle is similar to smooth muscle but is only located within the heart. This tissue is also controlled by involuntary processes. Cardiac muscle tissue doesn't contain nerves, but electrical impulses pass through the tissue causing involuntary responses.
Skeletal muscles are attached to bones in the body and are controlled through voluntary movements. When you do a push-up, flex your biceps, turn your head or scratch your nose with a finger, skeletal muscles are performing these tasks through voluntary movements.
