annalisevalerioti

[|mesodermal layer] of embryonic germ cells. [|Muscle cells] contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to produce [|force] and cause [|motion]. Muscles can cause either locomotion of the organism itself or movement of [|internal organs]. Cardiac and smooth muscle contraction occurs without [|conscious] thought and is necessary for survival. Examples are the contraction of the [|heart] and [|peristalsis] which pushes food through the [|digestive system]. Voluntary contraction of the skeletal muscles is used to move the body and can be finely controlled. Examples are movements of the eye, or gross movements like the [|quadriceps muscle] of the [|thigh]. There are two broad types of voluntary muscle fibers: slow twitch and fast twitch. Slow twitch fibers contract for long periods of time but with little force while fast twitch fibers contract quickly and powerfully but fatigue very rapidly. Muscles are predominately powered by the oxidation of fats and carbohydrates, but anaerobic chemical reactions are also used, particularly by fast twitch fibers. These chemical reactions produce [|adenosine triphosphate] (ATP) molecules which are used to power the movement of the myosin heads.