What is Muscle?
{{no sources}} {{confuse|Mussel}} '''Muscle''' is a [[tissue (biological)|tissue]] in animal [[body|bodies]]. Muscles are basically tissue which may contract (shorten). They usually attach to bones and are the way animals move. {{Infobox anatomy | Name = Muscular system | Latin = systema musculare | Image = Bougle whole2 retouched.png | Caption = The human muscles, seen from the front, 19th century illustration | Width = | Image2 = | Caption2 = | Precursor = | System = | Artery = | Vein = | Nerve = | Lymph = }} Their main purpose is to help us to move our body parts. They are one of the major systems of all animal bodies. When a muscle is activated it contracts, making itself shorter and thicker, thereby pulling its ends closer. == Types of muscles == There are three kinds of muscles: *[[Skeletal muscle]], the muscle attached to [[bone]]s. They pull on [[bone]]s to make movements. *[[Smooth muscle]], for example, the muscle in [[blood vessel]]s and the [[bladder]] *[[Cardiac muscle]], the muscle of the [[heart]] Muscle action can be classified as being either ''voluntary'' or ''involuntary''. <gallery> Image: Muscles anterior labeled.png|Skeletal muscles, viewed from the front Image: Muscle posterior labeled.png|Skeletal muscles, viewed from the back </gallery> The skeletal muscles move the limbs (arms and legs). They move the [[jaw]] up and down so that food can be [[chew]]ed. Skeletal muscles are the only ''voluntary'' muscles, the only ones that we can choose to move. The cardiac muscle is the muscle in the [[heart]]. When this muscle contracts it pushes blood through the [[circulatory system]]. The cardiac muscle is ''not'' voluntary. The smooth muscles are the other muscles in the body that are involuntary. Smooth muscles are in many places. They are in: *The [[gastrointestinal system]] – this includes the [[stomach]] and [[intestines]]. This is how food moves through us and we take energy from it. *[[Blood vessel]]s – smooth mus