By means of muscles the body – or parts of it – can move. In muscular tissue, theare extremely flexible. They are elongated in the direction of contraction and are organized in long muscle fibres. The body has three types of muscle tissue. Voluntary – or skeletal – muscles form the largest amount of muscle in the body. Under the microscope they look striped, because of the arrangement of the contractile molecules. Because they get their nervous impulses from the cerebral cortex, they are under voluntary control. They can contract very quickly, but they also fatigue very easily. Of course physical training can do a great deal to strengthen muscle: the muscle will become larger- not because of extra muscle fibres, but due to the individual thickening of the fibres.
Smooth muscle gets its name from the fact that it is not striped. These types of muscle can be found in the intestines and surrounding the arteries. At these places they are concerned with propelling food through the gut and maintaining normalpressure. They act slowly, but can sustain contraction for a very long time. As the muscles are activated by the autonomic nervous system, we do not have conscious control over them. Heart muscle has properties of both skeletal muscle and smooth muscle tissue. It is striped (and therefore is strong), but is under the control of the autonomic nervous system. Only the frequency which the heart beats is regulated by the autonomic nervous system, however, because heart muscle can itself generate and conduct an impulse that leads to a contraction.