So basically, we have our cardiac muscle cells that only contain a single nucleus, they also contain these special connecting regions known as intercalated discs. Now, cardiac muscle cells also contain relatively large mitochondria and that makes sense because the cardiac muscle cells are constantly working, they're constantly pumping that blood throughout the body and so they need to continually make that ATP and that's why they contain large mitochondria. Now, unlike skeletal muscle tissue, which is voluntary because it is controlled by the somatic nervous system, cardiac muscle cell is involuntary because it is controlled by the autonomic nervous system. Now, although it is controlled by the autonomic nervous system, certain cardiac muscle cells actually exhibit something called myogenic activity. And myogenic activity simply means that certain cardiac muscle cells inside the heart can actually initiate a contraction without a stimulus from the nervous system. And we'll talk more about that when we're going to discuss the cardiovascular system.