Muscles can relax, contract, and provide force to move bones and body parts. There are voluntary muscles that can be controlled and involuntary muscles that cannot be controlled, like the heart. Skeletal muscles move bones and are attached by tendons, while cardiac muscle is only found in the heart and contracts 70 times per minute. Skin is the body's largest organ consisting of three layers - epidermis, dermis and hypodermis. The dermis contains blood vessels, nerves, glands and binds skin to underlying tissue.