The muscle cells are elongated and for this reason also called muscle fibers.
There are three types of muscle cells with distinct morphological and functional features. All have contractile properties, in other words, they may shorten their lenghth and return to their former lenghth. They own distinct distributions in different organs and tissues.
All muscle fibers have in common:
– the presence in their cytoplasm of a large amount of proteins whose arrangement produces their contraction, primarily myosin and actin (also called contractile proteins) associated to several other proteins. Their organization of these proteins is similar in the striated muscle fibers and differs in the smooth muscle cells.
– the capacity to generate tension and movement resulting from their contraction. As these cells are elongated, they can undergo significant longitudinal reduction generating movement. A contraction without shortening results in tension.
Two types of muscle fibers form the striated muscle tissues due to the peculiar organization of their contractile proteins. Transverse bands can be observed along their cytoplasm when longitudinal sections of their fibers are viewed under a microscope. The arrangement of contractile proteins in the smooth muscle is quite different and as a consequence its cells do not show transverse bands.
Main features of muscle cells:
– Skeletal striated muscle – of voluntary contraction constitutes the body’s musculature attached to bones, as well as a few muscles not attached to bones, such as those present in the skin, the intrinsec muscles of the tongue, mimic muscles, the orbicularis oculi.
– Cardiac striated muscle – its contraction is involuntary. They are the muscle that make up the myocardium of the heart, also found in the initial portion of the aorta.
– Smooth muscle – its contraction is involuntary and constitutes the muscles of the viscera, of the walls of blood vessels and is found in several other places.